method chaining - Page 187

ASP.NET MVC 3 - New Features

- by imran_ku07

Introduction: ASP.NET MVC 3 just released by ASP.NET MVC team which includes some new features, some changes, some improvements and bug fixes. In this article, I will show you the new features of ASP.NET MVC 3. This will help you to get started using the new features of ASP.NET MVC 3. Full details of this announcement is available at Announcing release of ASP.NET MVC 3, IIS Express, SQL CE 4, Web Farm Framework, Orchard, WebMatrix. Description: New Razor View Engine: Razor view engine is one of the most coolest new feature in ASP.NET MVC 3. Razor is speeding things up just a little bit more. It is much smaller and lighter in size. Also it is very easy to learn. You can say ' write less, do more '. You can get start and learn more about Razor at Introducing “Razor” – a new view engine for ASP.NET. Granular Request Validation: Another biggest new feature in ASP.NET MVC 3 is Granular Request Validation. Default request validator will throw an exception when he see < followed by an exclamation(like <!) or < followed by the letters a through z(like <s) or & followed by a pound sign(like &#123) as a part of querystring, posted form, headers and cookie collection. In previous versions of ASP.NET MVC, you can control request validation using ValidateInputAttriubte. In ASP.NET MVC 3 you can control request validation at Model level by annotating your model properties with a new attribute called AllowHtmlAttribute. For details see Granular Request Validation in ASP.NET MVC 3. Sessionless Controller Support: Sessionless Controller is another great new feature in ASP.NET MVC 3. With Sessionless Controller you can easily control your session behavior for controllers. For example, you can make your HomeController's Session as Disabled or ReadOnly, allowing concurrent request execution for single user. For details see Concurrent Requests In ASP.NET MVC and HowTo: Sessionless Controller in MVC3 – what & and why?. Unobtrusive Ajax and Unobtrusive Client Side Validation is Supported: Another cool new feature in ASP.NET MVC 3 is support for Unobtrusive Ajax and Unobtrusive Client Side Validation. This feature allows separation of responsibilities within your web application by separating your html with your script. For details see Unobtrusive Ajax in ASP.NET MVC 3 and Unobtrusive Client Validation in ASP.NET MVC 3. Dependency Resolver: Dependency Resolver is another great feature of ASP.NET MVC 3. It allows you to register a dependency resolver that will be used by the framework. With this approach your application will not become tightly coupled and the dependency will be injected at run time. For details see ASP.NET MVC 3 Service Location. New Helper Methods: ASP.NET MVC 3 includes some helper methods of ASP.NET Web Pages technology that are used for common functionality. These helper methods includes: Chart, Crypto, WebGrid, WebImage and WebMail. For details of these helper methods, please see ASP.NET MVC 3 Release Notes. For using other helper methods of ASP.NET Web Pages see Using ASP.NET Web Pages Helpers in ASP.NET MVC. Child Action Output Caching: ASP.NET MVC 3 also includes another feature called Child Action Output Caching. This allows you to cache only a portion of the response when you are using Html.RenderAction or Html.Action. This cache can be varied by action name, action method signature and action method parameter values. For details see this. RemoteAttribute: ASP.NET MVC 3 allows you to validate a form field by making a remote server call through Ajax. This makes it very easy to perform remote validation at client side and quickly give the feedback to the user. For details see How to: Implement Remote Validation in ASP.NET MVC. CompareAttribute: ASP.NET MVC 3 includes a new validation attribute called CompareAttribute. CompareAttribute allows you to compare the values of two different properties of a model. For details see CompareAttribute in ASP.NET MVC 3. Miscellaneous New Features: ASP.NET MVC 2 includes FormValueProvider, QueryStringValueProvider, RouteDataValueProvider and HttpFileCollectionValueProvider. ASP.NET MVC 3 adds two additional value providers, ChildActionValueProvider and JsonValueProvider(JsonValueProvider is not physically exist). ChildActionValueProvider is used when you issue a child request using Html.Action and/or Html.RenderAction methods, so that your explicit parameter values in Html.Action and/or Html.RenderAction will always take precedence over other value providers. JsonValueProvider is used to model bind JSON data. For details see Sending JSON to an ASP.NET MVC Action Method Argument. In ASP.NET MVC 3, a new property named FileExtensions added to the VirtualPathProviderViewEngine class. This property is used when looking up a view by path (and not by name), so that only views with a file extension contained in the list specified by this new property is considered. For details see VirtualPathProviderViewEngine.FileExtensions Property . ASP.NET MVC 3 installation package also includes the NuGet Package Manager which will be automatically installed when you install ASP.NET MVC 3. NuGet makes it easy to install and update open source libraries and tools in Visual Studio. See this for details. In ASP.NET MVC 2, client side validation will not trigger for overridden model properties. For example, if have you a Model that contains some overridden properties then client side validation will not trigger for overridden properties in ASP.NET MVC 2 but client side validation will work for overridden properties in ASP.NET MVC 3. Client side validation is not supported for StringLengthAttribute.MinimumLength property in ASP.NET MVC 2. In ASP.NET MVC 3 client side validation will work for StringLengthAttribute.MinimumLength property. ASP.NET MVC 3 includes new action results like HttpUnauthorizedResult, HttpNotFoundResult and HttpStatusCodeResult. ASP.NET MVC 3 includes some new overloads of LabelFor and LabelForModel methods. For details see LabelExtensions.LabelForModel and LabelExtensions.LabelFor. In ASP.NET MVC 3, IControllerFactory includes a new method GetControllerSessionBehavior. This method is used to get controller's session behavior. For details see IControllerFactory.GetControllerSessionBehavior Method. In ASP.NET MVC 3, Controller class includes a new property ViewBag which is of type dynamic. This property allows you to access ViewData Dictionary using C # 4.0 dynamic features. For details see ControllerBase.ViewBag Property. ModelMetadata includes a property AdditionalValues which is of type Dictionary. In ASP.NET MVC 3 you can populate this property using AdditionalMetadataAttribute. For details see AdditionalMetadataAttribute Class. In ASP.NET MVC 3 you can also use MvcScaffolding to scaffold your Views and Controller. For details see Scaffold your ASP.NET MVC 3 project with the MvcScaffolding package. If you want to convert your application from ASP.NET MVC 2 to ASP.NET MVC 3 then there is an excellent tool that automatically converts ASP.NET MVC 2 application to ASP.NET MVC 3 application. For details see MVC 3 Project Upgrade Tool. In ASP.NET MVC 2 DisplayAttribute is not supported but in ASP.NET MVC 3 DisplayAttribute will work properly. ASP.NET MVC 3 also support model level validation via the new IValidatableObject interface. ASP.NET MVC 3 includes a new helper method Html.Raw. This helper method allows you to display unencoded HTML. Summary: In this article I showed you the new features of ASP.NET MVC 3. This will help you a lot when you start using ASP MVC 3. I also provide you the links where you can find further details. Hopefully you will enjoy this article too.

Read the article

Netflix, jQuery, JSONP, and OData

- by Stephen Walther

At the last MIX conference, Netflix announced that they are exposing their catalog of movie information using the OData protocol. This is great news! This means that you can take advantage of all of the advanced OData querying features against a live database of Netflix movies. In this blog entry, I’ll demonstrate how you can use Netflix, jQuery, JSONP, and OData to create a simple movie lookup form. The form enables you to enter a movie title, or part of a movie title, and display a list of matching movies. For example, Figure 1 illustrates the movies displayed when you enter the value robot into the lookup form. Using the Netflix OData Catalog API You can learn about the Netflix OData Catalog API at the following website: http://developer.netflix.com/docs/oData_Catalog The nice thing about this website is that it provides plenty of samples. It also has a good general reference for OData. For example, the website includes a list of OData filter operators and functions. The Netflix Catalog API exposes 4 top-level resources: Titles – A database of Movie information including interesting movie properties such as synopsis, BoxArt, and Cast. People – A database of people information including interesting information such as Awards, TitlesDirected, and TitlesActedIn. Languages – Enables you to get title information in different languages. Genres – Enables you to get title information for specific movie genres. OData is REST based. This means that you can perform queries by putting together the right URL. For example, if you want to get a list of the movies that were released after 2010 and that had an average rating greater than 4 then you can enter the following URL in the address bar of your browser: http://odata.netflix.com/Catalog/Titles?$filter=ReleaseYear gt 2010&AverageRating gt 4 Entering this URL returns the movies in Figure 2. Creating the Movie Lookup Form The complete code for the Movie Lookup form is contained in Listing 1. Listing 1 – MovieLookup.htm <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>Netflix with jQuery</title> <style type="text/css"> #movieTemplateContainer div { width:400px; padding: 10px; margin: 10px; border: black solid 1px; } </style> <script src="http://ajax.microsoft.com/ajax/jquery/jquery-1.4.2.js" type="text/javascript"></script> <script src="App_Scripts/Microtemplates.js" type="text/javascript"></script> </head> <body> <label>Search Movies:</label> <input id="movieName" size="50" /> <button id="btnLookup">Lookup</button> <div id="movieTemplateContainer"></div> <script id="movieTemplate" type="text/html"> <div> <img src="<%=BoxArtSmallUrl %>" /> <strong><%=Name%></strong> <p> <%=Synopsis %> </p> </div> </script> <script type="text/javascript"> $("#btnLookup").click(function () { // Build OData query var movieName = $("#movieName").val(); var query = "http://odata.netflix.com/Catalog" // netflix base url + "/Titles" // top-level resource + "?$filter=substringof('" + escape(movieName) + "',Name)" // filter by movie name + "&$callback=callback" // jsonp request + "&$format=json"; // json request // Make JSONP call to Netflix $.ajax({ dataType: "jsonp", url: query, jsonpCallback: "callback", success: callback }); }); function callback(result) { // unwrap result var movies = result["d"]["results"]; // show movies in template var showMovie = tmpl("movieTemplate"); var html = ""; for (var i = 0; i < movies.length; i++) { // flatten movie movies[i].BoxArtSmallUrl = movies[i].BoxArt.SmallUrl; // render with template html += showMovie(movies[i]); } $("#movieTemplateContainer").html(html); } </script> </body> </html> The HTML page in Listing 1 includes two JavaScript libraries: <script src="http://ajax.microsoft.com/ajax/jquery/jquery-1.4.2.js" type="text/javascript"></script> <script src="App_Scripts/Microtemplates.js" type="text/javascript"></script> The first script tag retrieves jQuery from the Microsoft Ajax CDN. You can learn more about the Microsoft Ajax CDN by visiting the following website: http://www.asp.net/ajaxLibrary/cdn.ashx The second script tag is used to reference Resig’s micro-templating library. Because I want to use a template to display each movie, I need this library: http://ejohn.org/blog/javascript-micro-templating/ When you enter a value into the Search Movies input field and click the button, the following JavaScript code is executed: // Build OData query var movieName = $("#movieName").val(); var query = "http://odata.netflix.com/Catalog" // netflix base url + "/Titles" // top-level resource + "?$filter=substringof('" + escape(movieName) + "',Name)" // filter by movie name + "&$callback=callback" // jsonp request + "&$format=json"; // json request // Make JSONP call to Netflix $.ajax({ dataType: "jsonp", url: query, jsonpCallback: "callback", success: callback }); This code Is used to build a query that will be executed against the Netflix Catalog API. For example, if you enter the search phrase King Kong then the following URL is created: http://odata.netflix.com/Catalog/Titles?$filter=substringof(‘King%20Kong’,Name)&$callback=callback&$format=json This query includes the following parameters: $filter – You assign a filter expression to this parameter to filter the movie results. $callback – You assign the name of a JavaScript callback method to this parameter. OData calls this method to return the movie results. $format – you assign either the value json or xml to this parameter to specify how the format of the movie results. Notice that all of the OData parameters -- $filter, $callback, $format -- start with a dollar sign $. The Movie Lookup form uses JSONP to retrieve data across the Internet. Because WCF Data Services supports JSONP, and Netflix uses WCF Data Services to expose movies using the OData protocol, you can use JSONP when interacting with the Netflix Catalog API. To learn more about using JSONP with OData, see Pablo Castro’s blog: http://blogs.msdn.com/pablo/archive/2009/02/25/adding-support-for-jsonp-and-url-controlled-format-to-ado-net-data-services.aspx The actual JSONP call is performed by calling the $.ajax() method. When this call successfully completes, the JavaScript callback() method is called. The callback() method looks like this: function callback(result) { // unwrap result var movies = result["d"]["results"]; // show movies in template var showMovie = tmpl("movieTemplate"); var html = ""; for (var i = 0; i < movies.length; i++) { // flatten movie movies[i].BoxArtSmallUrl = movies[i].BoxArt.SmallUrl; // render with template html += showMovie(movies[i]); } $("#movieTemplateContainer").html(html); } The movie results from Netflix are passed to the callback method. The callback method takes advantage of Resig’s micro-templating library to display each of the movie results. A template used to display each movie is passed to the tmpl() method. The movie template looks like this: <script id="movieTemplate" type="text/html"> <div> <img src="<%=BoxArtSmallUrl %>" /> <strong><%=Name%></strong> <p> <%=Synopsis %> </p> </div> </script> This template looks like a server-side ASP.NET template. However, the template is rendered in the client (browser) instead of the server. Summary The goal of this blog entry was to demonstrate how well jQuery works with OData. We managed to use a number of interesting open-source libraries and open protocols while building the Movie Lookup form including jQuery, JSONP, JSON, and OData.

Read the article

Using a WPF ListView as a DataGrid

- by psheriff

Many people like to view data in a grid format of rows and columns. WPF did not come with a data grid control that automatically creates rows and columns for you based on the object you pass it. However, the WPF Toolkit can be downloaded from CodePlex.com that does contain a DataGrid control. This DataGrid gives you the ability to pass it a DataTable or a Collection class and it will automatically figure out the columns or properties and create all the columns for you and display the data.The DataGrid control also supports editing and many other features that you might not always need. This means that the DataGrid does take a little more time to render the data. If you want to just display data (see Figure 1) in a grid format, then a ListView works quite well for this task. Of course, you will need to create the columns for the ListView, but with just a little generic code, you can create the columns on the fly just like the WPF Toolkit’s DataGrid. Figure 1: A List of Data using a ListView A Simple ListView ControlThe XAML below is what you would use to create the ListView shown in Figure 1. However, the problem with using XAML is you have to pre-define the columns. You cannot re-use this ListView except for “Product” data. <ListView x:Name="lstData" ItemsSource="{Binding}"> <ListView.View> <GridView> <GridViewColumn Header="Product ID" Width="Auto" DisplayMemberBinding="{Binding Path=ProductId}" /> <GridViewColumn Header="Product Name" Width="Auto" DisplayMemberBinding="{Binding Path=ProductName}" /> <GridViewColumn Header="Price" Width="Auto" DisplayMemberBinding="{Binding Path=Price}" /> </GridView> </ListView.View></ListView> So, instead of creating the GridViewColumn’s in XAML, let’s learn to create them in code to create any amount of columns in a ListView. Create GridViewColumn’s From Data TableTo display multiple columns in a ListView control you need to set its View property to a GridView collection object. You add GridViewColumn objects to the GridView collection and assign the GridView to the View property. Each GridViewColumn object needs to be bound to a column or property name of the object that the ListView will be bound to. An ADO.NET DataTable object contains a collection of columns, and these columns have a ColumnName property which you use to bind to the GridViewColumn objects. Listing 1 shows a sample of reading and XML file into a DataSet object. After reading the data a GridView object is created. You can then loop through the DataTable columns collection and create a GridViewColumn object for each column in the DataTable. Notice the DisplayMemberBinding property is set to a new Binding to the ColumnName in the DataTable. C#private void FirstSample(){ // Read the data DataSet ds = new DataSet(); ds.ReadXml(GetCurrentDirectory() + @"\Xml\Product.xml"); // Create the GridView GridView gv = new GridView(); // Create the GridView Columns foreach (DataColumn item in ds.Tables[0].Columns) { GridViewColumn gvc = new GridViewColumn(); gvc.DisplayMemberBinding = new Binding(item.ColumnName); gvc.Header = item.ColumnName; gvc.Width = Double.NaN; gv.Columns.Add(gvc); } // Setup the GridView Columns lstData.View = gv; // Display the Data lstData.DataContext = ds.Tables[0];} VB.NETPrivate Sub FirstSample() ' Read the data Dim ds As New DataSet() ds.ReadXml(GetCurrentDirectory() & "\Xml\Product.xml") ' Create the GridView Dim gv As New GridView() ' Create the GridView Columns For Each item As DataColumn In ds.Tables(0).Columns Dim gvc As New GridViewColumn() gvc.DisplayMemberBinding = New Binding(item.ColumnName) gvc.Header = item.ColumnName gvc.Width = [Double].NaN gv.Columns.Add(gvc) Next ' Setup the GridView Columns lstData.View = gv ' Display the Data lstData.DataContext = ds.Tables(0)End SubListing 1: Loop through the DataTable columns collection to create GridViewColumn objects A Generic Method for Creating a GridViewInstead of having to write the code shown in Listing 1 for each ListView you wish to create, you can create a generic method that given any DataTable will return a GridView column collection. Listing 2 shows how you can simplify the code in Listing 1 by setting up a class called WPFListViewCommon and create a method called CreateGridViewColumns that returns your GridView. C#private void DataTableSample(){ // Read the data DataSet ds = new DataSet(); ds.ReadXml(GetCurrentDirectory() + @"\Xml\Product.xml"); // Setup the GridView Columns lstData.View = WPFListViewCommon.CreateGridViewColumns(ds.Tables[0]); lstData.DataContext = ds.Tables[0];} VB.NETPrivate Sub DataTableSample() ' Read the data Dim ds As New DataSet() ds.ReadXml(GetCurrentDirectory() & "\Xml\Product.xml") ' Setup the GridView Columns lstData.View = _ WPFListViewCommon.CreateGridViewColumns(ds.Tables(0)) lstData.DataContext = ds.Tables(0)End SubListing 2: Call a generic method to create GridViewColumns. The CreateGridViewColumns MethodThe CreateGridViewColumns method will take a DataTable as a parameter and create a GridView object with a GridViewColumn object in its collection for each column in your DataTable. C#public static GridView CreateGridViewColumns(DataTable dt){ // Create the GridView GridView gv = new GridView(); gv.AllowsColumnReorder = true; // Create the GridView Columns foreach (DataColumn item in dt.Columns) { GridViewColumn gvc = new GridViewColumn(); gvc.DisplayMemberBinding = new Binding(item.ColumnName); gvc.Header = item.ColumnName; gvc.Width = Double.NaN; gv.Columns.Add(gvc); } return gv;} VB.NETPublic Shared Function CreateGridViewColumns _ (ByVal dt As DataTable) As GridView ' Create the GridView Dim gv As New GridView() gv.AllowsColumnReorder = True ' Create the GridView Columns For Each item As DataColumn In dt.Columns Dim gvc As New GridViewColumn() gvc.DisplayMemberBinding = New Binding(item.ColumnName) gvc.Header = item.ColumnName gvc.Width = [Double].NaN gv.Columns.Add(gvc) Next Return gvEnd FunctionListing 3: The CreateGridViewColumns method takes a DataTable and creates GridViewColumn objects in a GridView. By separating this method out into a class you can call this method anytime you want to create a ListView with a collection of columns from a DataTable. SummaryIn this blog you learned how to create a ListView that acts like a DataGrid. You are able to use a DataTable as both the source of the data, and for creating the columns for the ListView. In the next blog entry you will learn how to use the same technique, but for Collection classes. NOTE: You can download the complete sample code (in both VB and C#) at my website. http://www.pdsa.com/downloads. Choose Tips & Tricks, then "WPF ListView as a DataGrid" from the drop-down. Good Luck with your Coding,Paul Sheriff ** SPECIAL OFFER FOR MY BLOG READERS **Visit http://www.pdsa.com/Event/Blog for a free eBook on "Fundamentals of N-Tier".

Read the article

Parallelism in .NET – Part 7, Some Differences between PLINQ and LINQ to Objects

- by Reed

In my previous post on Declarative Data Parallelism, I mentioned that PLINQ extends LINQ to Objects to support parallel operations. Although nearly all of the same operations are supported, there are some differences between PLINQ and LINQ to Objects. By introducing Parallelism to our declarative model, we add some extra complexity. This, in turn, adds some extra requirements that must be addressed. In order to illustrate the main differences, and why they exist, let’s begin by discussing some differences in how the two technologies operate, and look at the underlying types involved in LINQ to Objects and PLINQ . LINQ to Objects is mainly built upon a single class: Enumerable. The Enumerable class is a static class that defines a large set of extension methods, nearly all of which work upon an IEnumerable<T>. Many of these methods return a new IEnumerable<T>, allowing the methods to be chained together into a fluent style interface. This is what allows us to write statements that chain together, and lead to the nice declarative programming model of LINQ: double min = collection .Where(item => item.SomeProperty > 6 && item.SomeProperty < 24) .Min(item => item.PerformComputation()); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Other LINQ variants work in a similar fashion. For example, most data-oriented LINQ providers are built upon an implementation of IQueryable<T>, which allows the database provider to turn a LINQ statement into an underlying SQL query, to be performed directly on the remote database. PLINQ is similar, but instead of being built upon the Enumerable class, most of PLINQ is built upon a new static class: ParallelEnumerable. When using PLINQ, you typically begin with any collection which implements IEnumerable<T>, and convert it to a new type using an extension method defined on ParallelEnumerable: AsParallel(). This method takes any IEnumerable<T>, and converts it into a ParallelQuery<T>, the core class for PLINQ. There is a similar ParallelQuery class for working with non-generic IEnumerable implementations. This brings us to our first subtle, but important difference between PLINQ and LINQ – PLINQ always works upon specific types, which must be explicitly created. Typically, the type you’ll use with PLINQ is ParallelQuery<T>, but it can sometimes be a ParallelQuery or an OrderedParallelQuery<T>. Instead of dealing with an interface, implemented by an unknown class, we’re dealing with a specific class type. This works seamlessly from a usage standpoint – ParallelQuery<T> implements IEnumerable<T>, so you can always “switch back” to an IEnumerable<T>. The difference only arises at the beginning of our parallelization. When we’re using LINQ, and we want to process a normal collection via PLINQ, we need to explicitly convert the collection into a ParallelQuery<T> by calling AsParallel(). There is an important consideration here – AsParallel() does not need to be called on your specific collection, but rather any IEnumerable<T>. This allows you to place it anywhere in the chain of methods involved in a LINQ statement, not just at the beginning. This can be useful if you have an operation which will not parallelize well or is not thread safe. For example, the following is perfectly valid, and similar to our previous examples: double min = collection .AsParallel() .Select(item => item.SomeOperation()) .Where(item => item.SomeProperty > 6 && item.SomeProperty < 24) .Min(item => item.PerformComputation()); However, if SomeOperation() is not thread safe, we could just as easily do: double min = collection .Select(item => item.SomeOperation()) .AsParallel() .Where(item => item.SomeProperty > 6 && item.SomeProperty < 24) .Min(item => item.PerformComputation()); In this case, we’re using standard LINQ to Objects for the Select(…) method, then converting the results of that map routine to a ParallelQuery<T>, and processing our filter (the Where method) and our aggregation (the Min method) in parallel. PLINQ also provides us with a way to convert a ParallelQuery<T> back into a standard IEnumerable<T>, forcing sequential processing via standard LINQ to Objects. If SomeOperation() was thread-safe, but PerformComputation() was not thread-safe, we would need to handle this by using the AsEnumerable() method: double min = collection .AsParallel() .Select(item => item.SomeOperation()) .Where(item => item.SomeProperty > 6 && item.SomeProperty < 24) .AsEnumerable() .Min(item => item.PerformComputation()); Here, we’re converting our collection into a ParallelQuery<T>, doing our map operation (the Select(…) method) and our filtering in parallel, then converting the collection back into a standard IEnumerable<T>, which causes our aggregation via Min() to be performed sequentially. This could also be written as two statements, as well, which would allow us to use the language integrated syntax for the first portion: var tempCollection = from item in collection.AsParallel() let e = item.SomeOperation() where (e.SomeProperty > 6 && e.SomeProperty < 24) select e; double min = tempCollection.AsEnumerable().Min(item => item.PerformComputation()); This allows us to use the standard LINQ style language integrated query syntax, but control whether it’s performed in parallel or serial by adding AsParallel() and AsEnumerable() appropriately. The second important difference between PLINQ and LINQ deals with order preservation. PLINQ, by default, does not preserve the order of of source collection. This is by design. In order to process a collection in parallel, the system needs to naturally deal with multiple elements at the same time. Maintaining the original ordering of the sequence adds overhead, which is, in many cases, unnecessary. Therefore, by default, the system is allowed to completely change the order of your sequence during processing. If you are doing a standard query operation, this is usually not an issue. However, there are times when keeping a specific ordering in place is important. If this is required, you can explicitly request the ordering be preserved throughout all operations done on a ParallelQuery<T> by using the AsOrdered() extension method. This will cause our sequence ordering to be preserved. For example, suppose we wanted to take a collection, perform an expensive operation which converts it to a new type, and display the first 100 elements. In LINQ to Objects, our code might look something like: // Using IEnumerable<SourceClass> collection IEnumerable<ResultClass> results = collection .Select(e => e.CreateResult()) .Take(100); If we just converted this to a parallel query naively, like so: IEnumerable<ResultClass> results = collection .AsParallel() .Select(e => e.CreateResult()) .Take(100); We could very easily get a very different, and non-reproducable, set of results, since the ordering of elements in the input collection is not preserved. To get the same results as our original query, we need to use: IEnumerable<ResultClass> results = collection .AsParallel() .AsOrdered() .Select(e => e.CreateResult()) .Take(100); This requests that PLINQ process our sequence in a way that verifies that our resulting collection is ordered as if it were processed serially. This will cause our query to run slower, since there is overhead involved in maintaining the ordering. However, in this case, it is required, since the ordering is required for correctness. PLINQ is incredibly useful. It allows us to easily take nearly any LINQ to Objects query and run it in parallel, using the same methods and syntax we’ve used previously. There are some important differences in operation that must be considered, however – it is not a free pass to parallelize everything. When using PLINQ in order to parallelize your routines declaratively, the same guideline I mentioned before still applies: Parallelization is something that should be handled with care and forethought, added by design, and not just introduced casually.

Read the article

Parallelism in .NET – Part 9, Configuration in PLINQ and TPL

- by Reed

Parallel LINQ and the Task Parallel Library contain many options for configuration. Although the default configuration options are often ideal, there are times when customizing the behavior is desirable. Both frameworks provide full configuration support. When working with Data Parallelism, there is one primary configuration option we often need to control – the number of threads we want the system to use when parallelizing our routine. By default, PLINQ and the TPL both use the ThreadPool to schedule tasks. Given the major improvements in the ThreadPool in CLR 4, this default behavior is often ideal. However, there are times that the default behavior is not appropriate. For example, if you are working on multiple threads simultaneously, and want to schedule parallel operations from within both threads, you might want to consider restricting each parallel operation to using a subset of the processing cores of the system. Not doing this might over-parallelize your routine, which leads to inefficiencies from having too many context switches. In the Task Parallel Library, configuration is handled via the ParallelOptions class. All of the methods of the Parallel class have an overload which accepts a ParallelOptions argument. We configure the Parallel class by setting the ParallelOptions.MaxDegreeOfParallelism property. For example, let’s revisit one of the simple data parallel examples from Part 2: Parallel.For(0, pixelData.GetUpperBound(0), row => { for (int col=0; col < pixelData.GetUpperBound(1); ++col) { pixelData[row, col] = AdjustContrast(pixelData[row, col], minPixel, maxPixel); } }); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Here, we’re looping through an image, and calling a method on each pixel in the image. If this was being done on a separate thread, and we knew another thread within our system was going to be doing a similar operation, we likely would want to restrict this to using half of the cores on the system. This could be accomplished easily by doing: var options = new ParallelOptions(); options.MaxDegreeOfParallelism = Math.Max(Environment.ProcessorCount / 2, 1); Parallel.For(0, pixelData.GetUpperBound(0), options, row => { for (int col=0; col < pixelData.GetUpperBound(1); ++col) { pixelData[row, col] = AdjustContrast(pixelData[row, col], minPixel, maxPixel); } }); Now, we’re restricting this routine to using no more than half the cores in our system. Note that I included a check to prevent a single core system from supplying zero; without this check, we’d potentially cause an exception. I also did not hard code a specific value for the MaxDegreeOfParallelism property. One of our goals when parallelizing a routine is allowing it to scale on better hardware. Specifying a hard-coded value would contradict that goal. Parallel LINQ also supports configuration, and in fact, has quite a few more options for configuring the system. The main configuration option we most often need is the same as our TPL option: we need to supply the maximum number of processing threads. In PLINQ, this is done via a new extension method on ParallelQuery<T>: ParallelEnumerable.WithDegreeOfParallelism. Let’s revisit our declarative data parallelism sample from Part 6: double min = collection.AsParallel().Min(item => item.PerformComputation()); Here, we’re performing a computation on each element in the collection, and saving the minimum value of this operation. If we wanted to restrict this to a limited number of threads, we would add our new extension method: int maxThreads = Math.Max(Environment.ProcessorCount / 2, 1); double min = collection .AsParallel() .WithDegreeOfParallelism(maxThreads) .Min(item => item.PerformComputation()); This automatically restricts the PLINQ query to half of the threads on the system. PLINQ provides some additional configuration options. By default, PLINQ will occasionally revert to processing a query in parallel. This occurs because many queries, if parallelized, typically actually cause an overall slowdown compared to a serial processing equivalent. By analyzing the “shape” of the query, PLINQ often decides to run a query serially instead of in parallel. This can occur for (taken from MSDN): Queries that contain a Select, indexed Where, indexed SelectMany, or ElementAt clause after an ordering or filtering operator that has removed or rearranged original indices. Queries that contain a Take, TakeWhile, Skip, SkipWhile operator and where indices in the source sequence are not in the original order. Queries that contain Zip or SequenceEquals, unless one of the data sources has an originally ordered index and the other data source is indexable (i.e. an array or IList(T)). Queries that contain Concat, unless it is applied to indexable data sources. Queries that contain Reverse, unless applied to an indexable data source. If the specific query follows these rules, PLINQ will run the query on a single thread. However, none of these rules look at the specific work being done in the delegates, only at the “shape” of the query. There are cases where running in parallel may still be beneficial, even if the shape is one where it typically parallelizes poorly. In these cases, you can override the default behavior by using the WithExecutionMode extension method. This would be done like so: var reversed = collection .AsParallel() .WithExecutionMode(ParallelExecutionMode.ForceParallelism) .Select(i => i.PerformComputation()) .Reverse(); Here, the default behavior would be to not parallelize the query unless collection implemented IList<T>. We can force this to run in parallel by adding the WithExecutionMode extension method in the method chain. Finally, PLINQ has the ability to configure how results are returned. When a query is filtering or selecting an input collection, the results will need to be streamed back into a single IEnumerable<T> result. For example, the method above returns a new, reversed collection. In this case, the processing of the collection will be done in parallel, but the results need to be streamed back to the caller serially, so they can be enumerated on a single thread. This streaming introduces overhead. IEnumerable<T> isn’t designed with thread safety in mind, so the system needs to handle merging the parallel processes back into a single stream, which introduces synchronization issues. There are two extremes of how this could be accomplished, but both extremes have disadvantages. The system could watch each thread, and whenever a thread produces a result, take that result and send it back to the caller. This would mean that the calling thread would have access to the data as soon as data is available, which is the benefit of this approach. However, it also means that every item is introducing synchronization overhead, since each item needs to be merged individually. On the other extreme, the system could wait until all of the results from all of the threads were ready, then push all of the results back to the calling thread in one shot. The advantage here is that the least amount of synchronization is added to the system, which means the query will, on a whole, run the fastest. However, the calling thread will have to wait for all elements to be processed, so this could introduce a long delay between when a parallel query begins and when results are returned. The default behavior in PLINQ is actually between these two extremes. By default, PLINQ maintains an internal buffer, and chooses an optimal buffer size to maintain. Query results are accumulated into the buffer, then returned in the IEnumerable<T> result in chunks. This provides reasonably fast access to the results, as well as good overall throughput, in most scenarios. However, if we know the nature of our algorithm, we may decide we would prefer one of the other extremes. This can be done by using the WithMergeOptions extension method. For example, if we know that our PerformComputation() routine is very slow, but also variable in runtime, we may want to retrieve results as they are available, with no bufferring. This can be done by changing our above routine to: var reversed = collection .AsParallel() .WithExecutionMode(ParallelExecutionMode.ForceParallelism) .WithMergeOptions(ParallelMergeOptions.NotBuffered) .Select(i => i.PerformComputation()) .Reverse(); On the other hand, if are already on a background thread, and we want to allow the system to maximize its speed, we might want to allow the system to fully buffer the results: var reversed = collection .AsParallel() .WithExecutionMode(ParallelExecutionMode.ForceParallelism) .WithMergeOptions(ParallelMergeOptions.FullyBuffered) .Select(i => i.PerformComputation()) .Reverse(); Notice, also, that you can specify multiple configuration options in a parallel query. By chaining these extension methods together, we generate a query that will always run in parallel, and will always complete before making the results available in our IEnumerable<T>.

Read the article

ASP.NET MVC ‘Extendable-hooks’ – ControllerActionInvoker class

- by nmarun

There’s a class ControllerActionInvoker in ASP.NET MVC. This can be used as one of an hook-points to allow customization of your application. Watching Brad Wilsons’ Advanced MP3 from MVC Conf inspired me to write about this class. What MSDN says: “Represents a class that is responsible for invoking the action methods of a controller.” Well if MSDN says it, I think I can instill a fair amount of confidence into what the class does. But just to get to the details, I also looked into the source code for MVC. Seems like the base class Controller is where an IActionInvoker is initialized: 1: protected virtual IActionInvoker CreateActionInvoker() { 2: return new ControllerActionInvoker(); 3: } In the ControllerActionInvoker (the O-O-B behavior), there are different ‘versions’ of InvokeActionMethod() method that actually call the action method in question and return an instance of type ActionResult. 1: protected virtual ActionResult InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary<string, object> parameters) { 2: object returnValue = actionDescriptor.Execute(controllerContext, parameters); 3: ActionResult result = CreateActionResult(controllerContext, actionDescriptor, returnValue); 4: return result; 5: } I guess that’s enough on the ‘behind-the-screens’ of this class. Let’s see how we can use this class to hook-up extensions. Say I have a requirement that the user should be able to get different renderings of the same output, like html, xml, json, csv and so on. The user will type-in the output format in the url and should the get result accordingly. For example: http://site.com/RenderAs/ – renders the default way (the razor view) http://site.com/RenderAs/xml http://site.com/RenderAs/csv … and so on where RenderAs is my controller. There are many ways of doing this and I’m using a custom ControllerActionInvoker class (even though this might not be the best way to accomplish this). For this, my one and only route in the Global.asax.cs is: 1: routes.MapRoute("RenderAsRoute", "RenderAs/{outputType}", 2: new {controller = "RenderAs", action = "Index", outputType = ""}); Here the controller name is ‘RenderAsController’ and the action that’ll get called (always) is the Index action. The outputType parameter will map to the type of output requested by the user (xml, csv…). I intend to display a list of food items for this example. 1: public class Item 2: { 3: public int Id { get; set; } 4: public string Name { get; set; } 5: public Cuisine Cuisine { get; set; } 6: } 7: 8: public class Cuisine 9: { 10: public int CuisineId { get; set; } 11: public string Name { get; set; } 12: } Coming to my ‘RenderAsController’ class. I generate an IList<Item> to represent my model. 1: private static IList<Item> GetItems() 2: { 3: Cuisine cuisine = new Cuisine { CuisineId = 1, Name = "Italian" }; 4: Item item = new Item { Id = 1, Name = "Lasagna", Cuisine = cuisine }; 5: IList<Item> items = new List<Item> { item }; 6: item = new Item {Id = 2, Name = "Pasta", Cuisine = cuisine}; 7: items.Add(item); 8: //... 9: return items; 10: } My action method looks like 1: public IList<Item> Index(string outputType) 2: { 3: return GetItems(); 4: } There are two things that stand out in this action method. The first and the most obvious one being that the return type is not of type ActionResult (or one of its derivatives). Instead I’m passing the type of the model itself (IList<Item> in this case). We’ll convert this to some type of an ActionResult in our custom controller action invoker class later. The second thing (a little subtle) is that I’m not doing anything with the outputType value that is passed on to this action method. This value will be in the RouteData dictionary and we’ll use this in our custom invoker class as well. It’s time to hook up our invoker class. First, I’ll override the Initialize() method of my RenderAsController class. 1: protected override void Initialize(RequestContext requestContext) 2: { 3: base.Initialize(requestContext); 4: string outputType = string.Empty; 5: 6: // read the outputType from the RouteData dictionary 7: if (requestContext.RouteData.Values["outputType"] != null) 8: { 9: outputType = requestContext.RouteData.Values["outputType"].ToString(); 10: } 11: 12: // my custom invoker class 13: ActionInvoker = new ContentRendererActionInvoker(outputType); 14: } Coming to the main part of the discussion – the ContentRendererActionInvoker class: 1: public class ContentRendererActionInvoker : ControllerActionInvoker 2: { 3: private readonly string _outputType; 4: 5: public ContentRendererActionInvoker(string outputType) 6: { 7: _outputType = outputType.ToLower(); 8: } 9: //... 10: } So the outputType value that was read from the RouteData, which was passed in from the url, is being set here in a private field. Moving to the crux of this article, I now override the CreateActionResult method. 1: protected override ActionResult CreateActionResult(ControllerContext controllerContext, ActionDescriptor actionDescriptor, object actionReturnValue) 2: { 3: if (actionReturnValue == null) 4: return new EmptyResult(); 5: 6: ActionResult result = actionReturnValue as ActionResult; 7: if (result != null) 8: return result; 9: 10: // This is where the magic happens 11: // Depending on the value in the _outputType field, 12: // return an appropriate ActionResult 13: switch (_outputType) 14: { 15: case "json": 16: { 17: JavaScriptSerializer serializer = new JavaScriptSerializer(); 18: string json = serializer.Serialize(actionReturnValue); 19: return new ContentResult { Content = json, ContentType = "application/json" }; 20: } 21: case "xml": 22: { 23: XmlSerializer serializer = new XmlSerializer(actionReturnValue.GetType()); 24: using (StringWriter writer = new StringWriter()) 25: { 26: serializer.Serialize(writer, actionReturnValue); 27: return new ContentResult { Content = writer.ToString(), ContentType = "text/xml" }; 28: } 29: } 30: case "csv": 31: controllerContext.HttpContext.Response.AddHeader("Content-Disposition", "attachment; filename=items.csv"); 32: return new ContentResult 33: { 34: Content = ToCsv(actionReturnValue as IList<Item>), 35: ContentType = "application/ms-excel" 36: }; 37: case "pdf": 38: string filePath = controllerContext.HttpContext.Server.MapPath("~/items.pdf"); 39: controllerContext.HttpContext.Response.AddHeader("content-disposition", 40: "attachment; filename=items.pdf"); 41: ToPdf(actionReturnValue as IList<Item>, filePath); 42: return new FileContentResult(StreamFile(filePath), "application/pdf"); 43: 44: default: 45: controllerContext.Controller.ViewData.Model = actionReturnValue; 46: return new ViewResult 47: { 48: TempData = controllerContext.Controller.TempData, 49: ViewData = controllerContext.Controller.ViewData 50: }; 51: } 52: } A big method there! The hook I was talking about kinda above actually is here. This is where different kinds / formats of output get returned based on the output type requested in the url. When the _outputType is not set (string.Empty as set in the Global.asax.cs file), the razor view gets rendered (lines 45-50). This is the default behavior in most MVC applications where-in a view (webform/razor) gets rendered on the browser. As you see here, this gets returned as a ViewResult. But then, for an outputType of json/xml/csv, a ContentResult gets returned, while for pdf, a FileContentResult is returned. Here are how the different kinds of output look like: This is how we can leverage this feature of ASP.NET MVC to developer a better application. I’ve used the iTextSharp library to convert to a pdf format. Mike gives quite a bit of detail regarding this library here. You can download the sample code here. (You’ll get an option to download once you open the link). Verdict: Hot chocolate: $3; Reebok shoes: $50; Your first car: $3000; Being able to extend a web application: Priceless.

Read the article

C#: Adding Functionality to 3rd Party Libraries With Extension Methods

- by James Michael Hare

Ever have one of those third party libraries that you love but it's missing that one feature or one piece of syntactical candy that would make it so much more useful? This, I truly think, is one of the best uses of extension methods. I began discussing extension methods in my last post (which you find here) where I expounded upon what I thought were some rules of thumb for using extension methods correctly. As long as you keep in line with those (or similar) rules, they can often be useful for adding that little extra functionality or syntactical simplification for a library that you have little or no control over. Oh sure, you could take an open source project, download the source and add the methods you want, but then every time the library is updated you have to re-add your changes, which can be cumbersome and error prone. And yes, you could possibly extend a class in a third party library and override features, but that's only if the class is not sealed, static, or constructed via factories. This is the perfect place to use an extension method! And the best part is, you and your development team don't need to change anything! Simply add the using for the namespace the extensions are in! So let's consider this example. I love log4net! Of all the logging libraries I've played with, it, to me, is one of the most flexible and configurable logging libraries and it performs great. But this isn't about log4net, well, not directly. So why would I want to add functionality? Well, it's missing one thing I really want in the ILog interface: ability to specify logging level at runtime. For example, let's say I declare my ILog instance like so: using log4net; public class LoggingTest { private static readonly ILog _log = LogManager.GetLogger(typeof(LoggingTest)); ... } If you don't know log4net, the details aren't important, just to show that the field _log is the logger I have gotten from log4net. So now that I have that, I can log to it like so: _log.Debug("This is the lowest level of logging and just for debugging output."); _log.Info("This is an informational message. Usual normal operation events."); _log.Warn("This is a warning, something suspect but not necessarily wrong."); _log.Error("This is an error, some sort of processing problem has happened."); _log.Fatal("Fatals usually indicate the program is dying hideously."); And there's many flavors of each of these to log using string formatting, to log exceptions, etc. But one thing there isn't: the ability to easily choose the logging level at runtime. Notice, the logging levels above are chosen at compile time. Of course, you could do some fun stuff with lambdas and wrap it, but that would obscure the simplicity of the interface. And yes there is a Logger property you can dive down into where you can specify a Level, but the Level properties don't really match the ILog interface exactly and then you have to manually build a LogEvent and... well, it gets messy. I want something simple and sexy so I can say: _log.Log(someLevel, "This will be logged at whatever level I choose at runtime!"); Now, some purists out there might say you should always know what level you want to log at, and for the most part I agree with them. For the most party the ILog interface satisfies 99% of my needs. In fact, for most application logging yes you do always know the level you will be logging at, but when writing a utility class, you may not always know what level your user wants. I'll tell you, one of my favorite things is to write reusable components. If I had my druthers I'd write framework libraries and shared components all day! And being able to easily log at a runtime-chosen level is a big need for me. After all, if I want my code to really be re-usable, I shouldn't force a user to deal with the logging level I choose. One of my favorite uses for this is in Interceptors -- I'll describe Interceptors in my next post and some of my favorites -- for now just know that an Interceptor wraps a class and allows you to add functionality to an existing method without changing it's signature. At the risk of over-simplifying, it's a very generic implementation of the Decorator design pattern. So, say for example that you were writing an Interceptor that would time method calls and emit a log message if the method call execution time took beyond a certain threshold of time. For instance, maybe if your database calls take more than 5,000 ms, you want to log a warning. Or if a web method call takes over 1,000 ms, you want to log an informational message. This would be an excellent use of logging at a generic level. So here was my personal wish-list of requirements for my task: Be able to determine if a runtime-specified logging level is enabled. Be able to log generically at a runtime-specified logging level. Have the same look-and-feel of the existing Debug, Info, Warn, Error, and Fatal calls. Having the ability to also determine if logging for a level is on at runtime is also important so you don't spend time building a potentially expensive logging message if that level is off. Consider an Interceptor that may log parameters on entrance to the method. If you choose to log those parameter at DEBUG level and if DEBUG is not on, you don't want to spend the time serializing those parameters. Now, mine may not be the most elegant solution, but it performs really well since the enum I provide all uses contiguous values -- while it's never guaranteed, contiguous switch values usually get compiled into a jump table in IL which is VERY performant - O(1) - but even if it doesn't, it's still so fast you'd never need to worry about it. So first, I need a way to let users pass in logging levels. Sure, log4net has a Level class, but it's a class with static members and plus it provides way too many options compared to ILog interface itself -- and wouldn't perform as well in my level-check -- so I define an enum like below. namespace Shared.Logging.Extensions { // enum to specify available logging levels. public enum LoggingLevel { Debug, Informational, Warning, Error, Fatal } } Now, once I have this, writing the extension methods I need is trivial. Once again, I would typically /// comment fully, but I'm eliminating for blogging brevity: namespace Shared.Logging.Extensions { // the extension methods to add functionality to the ILog interface public static class LogExtensions { // Determines if logging is enabled at a given level. public static bool IsLogEnabled(this ILog logger, LoggingLevel level) { switch (level) { case LoggingLevel.Debug: return logger.IsDebugEnabled; case LoggingLevel.Informational: return logger.IsInfoEnabled; case LoggingLevel.Warning: return logger.IsWarnEnabled; case LoggingLevel.Error: return logger.IsErrorEnabled; case LoggingLevel.Fatal: return logger.IsFatalEnabled; } return false; } // Logs a simple message - uses same signature except adds LoggingLevel public static void Log(this ILog logger, LoggingLevel level, object message) { switch (level) { case LoggingLevel.Debug: logger.Debug(message); break; case LoggingLevel.Informational: logger.Info(message); break; case LoggingLevel.Warning: logger.Warn(message); break; case LoggingLevel.Error: logger.Error(message); break; case LoggingLevel.Fatal: logger.Fatal(message); break; } } // Logs a message and exception to the log at specified level. public static void Log(this ILog logger, LoggingLevel level, object message, Exception exception) { switch (level) { case LoggingLevel.Debug: logger.Debug(message, exception); break; case LoggingLevel.Informational: logger.Info(message, exception); break; case LoggingLevel.Warning: logger.Warn(message, exception); break; case LoggingLevel.Error: logger.Error(message, exception); break; case LoggingLevel.Fatal: logger.Fatal(message, exception); break; } } // Logs a formatted message to the log at the specified level. public static void LogFormat(this ILog logger, LoggingLevel level, string format, params object[] args) { switch (level) { case LoggingLevel.Debug: logger.DebugFormat(format, args); break; case LoggingLevel.Informational: logger.InfoFormat(format, args); break; case LoggingLevel.Warning: logger.WarnFormat(format, args); break; case LoggingLevel.Error: logger.ErrorFormat(format, args); break; case LoggingLevel.Fatal: logger.FatalFormat(format, args); break; } } } } So there it is! I didn't have to modify the log4net source code, so if a new version comes out, i can just add the new assembly with no changes. I didn't have to subclass and worry about developers not calling my sub-class instead of the original. I simply provide the extension methods and it's as if the long lost extension methods were always a part of the ILog interface! Consider a very contrived example using the original interface: // using the original ILog interface public class DatabaseUtility { private static readonly ILog _log = LogManager.Create(typeof(DatabaseUtility)); // some theoretical method to time IDataReader Execute(string statement) { var timer = new System.Diagnostics.Stopwatch(); // do DB magic // this is hard-coded to warn, if want to change at runtime tough luck! if (timer.ElapsedMilliseconds > 5000 && _log.IsWarnEnabled) { _log.WarnFormat("Statement {0} took too long to execute.", statement); } ... } } Now consider this alternate call where the logging level could be perhaps a property of the class // using the original ILog interface public class DatabaseUtility { private static readonly ILog _log = LogManager.Create(typeof(DatabaseUtility)); // allow logging level to be specified by user of class instead public LoggingLevel ThresholdLogLevel { get; set; } // some theoretical method to time IDataReader Execute(string statement) { var timer = new System.Diagnostics.Stopwatch(); // do DB magic // this is hard-coded to warn, if want to change at runtime tough luck! if (timer.ElapsedMilliseconds > 5000 && _log.IsLogEnabled(ThresholdLogLevel)) { _log.LogFormat(ThresholdLogLevel, "Statement {0} took too long to execute.", statement); } ... } } Next time, I'll show one of my favorite uses for these extension methods in an Interceptor.

Read the article

What is Polymorphism?

- by SAMIR BHOGAYTA

* Polymorphism is one of the primary characteristics (concept) of object-oriented programming. * Poly means many and morph means form. Thus, polymorphism refers to being able to use many forms of a type without regard to the details. * Polymorphism is the characteristic of being able to assign a different meaning specifically, to allow an entity such as a variable, a function, or an object to have more than one form. * Polymorphism is the ability to process objects differently depending on their data types. * Polymorphism is the ability to redefine methods for derived classes. Types of Polymorphism * Compile time Polymorphism * Run time Polymorphism Compile time Polymorphism * Compile time Polymorphism also known as method overloading * Method overloading means having two or more methods with the same name but with different signatures Example of Compile time polymorphism public class Calculations { public int add(int x, int y) { return x+y; } public int add(int x, int y, int z) { return x+y+z; } } Run time Polymorphism * Run time Polymorphism also known as method overriding * Method overriding means having two or more methods with the same name , same signature but with different implementation Example of Run time Polymorphism class Circle { public int radius = 0; public double getArea() { return 3.14 * radius * radius } } class Sphere { public double getArea() { return 4 * 3.14 * radius * radius } }

Read the article

Demystifying Silverlight Dependency Properties

- by dwahlin

I have the opportunity to teach a lot of people about Silverlight (amongst other technologies) and one of the topics that definitely confuses people initially is the concept of dependency properties. I confess that when I first heard about them my initial thought was “Why do we need a specialized type of property?” While you can certainly use standard CLR properties in Silverlight applications, Silverlight relies heavily on dependency properties for just about everything it does behind the scenes. In fact, dependency properties are an essential part of the data binding, template, style and animation functionality available in Silverlight. They simply back standard CLR properties. In this post I wanted to put together a (hopefully) simple explanation of dependency properties and why you should care about them if you’re currently working with Silverlight or looking to move to it. What are Dependency Properties? XAML provides a great way to define layout controls, user input controls, shapes, colors and data binding expressions in a declarative manner. There’s a lot that goes on behind the scenes in order to make XAML work and an important part of that magic is the use of dependency properties. If you want to bind data to a property, style it, animate it or transform it in XAML then the property involved has to be a dependency property to work properly. If you’ve ever positioned a control in a Canvas using Canvas.Left or placed a control in a specific Grid row using Grid.Row then you’ve used an attached property which is a specialized type of dependency property. Dependency properties play a key role in XAML and the overall Silverlight framework. Any property that you bind, style, template, animate or transform must be a dependency property in Silverlight applications. You can programmatically bind values to controls and work with standard CLR properties, but if you want to use the built-in binding expressions available in XAML (one of my favorite features) or the Binding class available through code then dependency properties are a necessity. Dependency properties aren’t needed in every situation, but if you want to customize your application very much you’ll eventually end up needing them. For example, if you create a custom user control and want to expose a property that consumers can use to change the background color, you have to define it as a dependency property if you want bindings, styles and other features to be available for use. Now that the overall purpose of dependency properties has been discussed let’s take a look at how you can create them. Creating Dependency Properties When .NET first came out you had to write backing fields for each property that you defined as shown next: Brush _ScheduleBackground; public Brush ScheduleBackground { get { return _ScheduleBackground; } set { _ScheduleBackground = value; } } Although .NET 2.0 added auto-implemented properties (for example: public Brush ScheduleBackground { get; set; }) where the compiler would automatically generate the backing field used by get and set blocks, the concept is still the same as shown in the above code; a property acts as a wrapper around a field. Silverlight dependency properties replace the _ScheduleBackground field shown in the previous code and act as the backing store for a standard CLR property. The following code shows an example of defining a dependency property named ScheduleBackgroundProperty: public static readonly DependencyProperty ScheduleBackgroundProperty = DependencyProperty.Register("ScheduleBackground", typeof(Brush), typeof(Scheduler), null); Looking through the code the first thing that may stand out is that the definition for ScheduleBackgroundProperty is marked as static and readonly and that the property appears to be of type DependencyProperty. This is a standard pattern that you’ll use when working with dependency properties. You’ll also notice that the property explicitly adds the word “Property” to the name which is another standard you’ll see followed. In addition to defining the property, the code also makes a call to the static DependencyProperty.Register method and passes the name of the property to register (ScheduleBackground in this case) as a string. The type of the property, the type of the class that owns the property and a null value (more on the null value later) are also passed. In this example a class named Scheduler acts as the owner. The code handles registering the property as a dependency property with the call to Register(), but there’s a little more work that has to be done to allow a value to be assigned to and retrieved from the dependency property. The following code shows the complete code that you’ll typically use when creating a dependency property. You can find code snippets that greatly simplify the process of creating dependency properties out on the web. The MVVM Light download available from http://mvvmlight.codeplex.com comes with built-in dependency properties snippets as well. public static readonly DependencyProperty ScheduleBackgroundProperty = DependencyProperty.Register("ScheduleBackground", typeof(Brush), typeof(Scheduler), null); public Brush ScheduleBackground { get { return (Brush)GetValue(ScheduleBackgroundProperty); } set { SetValue(ScheduleBackgroundProperty, value); } } The standard CLR property code shown above should look familiar since it simply wraps the dependency property. However, you’ll notice that the get and set blocks call GetValue and SetValue methods respectively to perform the appropriate operation on the dependency property. GetValue and SetValue are members of the DependencyObject class which is another key component of the Silverlight framework. Silverlight controls and classes (TextBox, UserControl, CompositeTransform, DataGrid, etc.) ultimately derive from DependencyObject in their inheritance hierarchy so that they can support dependency properties. Dependency properties defined in Silverlight controls and other classes tend to follow the pattern of registering the property by calling Register() and then wrapping the dependency property in a standard CLR property (as shown above). They have a standard property that wraps a registered dependency property and allows a value to be assigned and retrieved. If you need to expose a new property on a custom control that supports data binding expressions in XAML then you’ll follow this same pattern. Dependency properties are extremely useful once you understand why they’re needed and how they’re defined. Detecting Changes and Setting Defaults When working with dependency properties there will be times when you want to assign a default value or detect when a property changes so that you can keep the user interface in-sync with the property value. Silverlight’s DependencyProperty.Register() method provides a fourth parameter that accepts a PropertyMetadata object instance. PropertyMetadata can be used to hook a callback method to a dependency property. The callback method is called when the property value changes. PropertyMetadata can also be used to assign a default value to the dependency property. By assigning a value of null for the final parameter passed to Register() you’re telling the property that you don’t care about any changes and don’t have a default value to apply. Here are the different constructor overloads available on the PropertyMetadata class: PropertyMetadata Constructor Overload Description PropertyMetadata(Object) Used to assign a default value to a dependency property. PropertyMetadata(PropertyChangedCallback) Used to assign a property changed callback method. PropertyMetadata(Object, PropertyChangedCalback) Used to assign a default property value and a property changed callback. There are many situations where you need to know when a dependency property changes or where you want to apply a default. Performing either task is easily accomplished by creating a new instance of the PropertyMetadata class and passing the appropriate values to its constructor. The following code shows an enhanced version of the initial dependency property code shown earlier that demonstrates these concepts: public Brush ScheduleBackground { get { return (Brush)GetValue(ScheduleBackgroundProperty); } set { SetValue(ScheduleBackgroundProperty, value); } } public static readonly DependencyProperty ScheduleBackgroundProperty = DependencyProperty.Register("ScheduleBackground", typeof(Brush), typeof(Scheduler), new PropertyMetadata(new SolidColorBrush(Colors.LightGray), ScheduleBackgroundChanged)); private static void ScheduleBackgroundChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { var scheduler = d as Scheduler; scheduler.Background = e.NewValue as Brush; } The code wires ScheduleBackgroundProperty to a property change callback method named ScheduleBackgroundChanged. What’s interesting is that this callback method is static (as is the dependency property) so it gets passed the instance of the object that owns the property that has changed (otherwise we wouldn’t be able to get to the object instance). In this example the dependency object is cast to a Scheduler object and its Background property is assigned to the new value of the dependency property. The code also handles assigning a default value of LightGray to the dependency property by creating a new instance of a SolidColorBrush. To Sum Up In this post you’ve seen the role of dependency properties and how they can be defined in code. They play a big role in XAML and the overall Silverlight framework. You can think of dependency properties as being replacements for fields that you’d normally use with standard CLR properties. In addition to a discussion on how dependency properties are created, you also saw how to use the PropertyMetadata class to define default dependency property values and hook a dependency property to a callback method. The most important thing to understand with dependency properties (especially if you’re new to Silverlight) is that they’re needed if you want a property to support data binding, animations, transformations and styles properly. Any time you create a property on a custom control or user control that has these types of requirements you’ll want to pick a dependency property over of a standard CLR property with a backing field. There’s more that can be covered with dependency properties including a related property called an attached property….more to come.

Read the article

SQL SERVER – Attach or Detach Database – SQL in Sixty Seconds #068

- by Pinal Dave

When we have to move a database from one server to another server or when we have to move a database from one file to another file, we commonly use Database Attach or Detach process. I have been doing this for quite a while as well. Recently, when I was visiting an organization I found that in this organization lots of developers are still using an older version of the code to attach the database. I quickly pointed that out to them the new method to attach the database, however it was really interesting to find out that they really did not know that sp_attach_db is now a deprecated method to attach the database. This really made me to do today’s SQL in Sixty Seconds. I demonstrate in this SQL in Sixty Seconds how to attach or detach the database using a new method of attaching database. The code which I have used in this code is over here: -- Detach Database USE [master] GO EXEC MASTER.dbo.sp_detach_db @dbname = N'AdventureWorks2014_new' GO -- Deprecated Way to Attach Database USE [master] GO EXEC MASTER.dbo.sp_attach_db 'AdventureWorks2014_new', 'E:\AdventureWorks2012_Data_new.mdf', 'E:\AdventureWorks2012_log_new.ldf' GO -- Correct Way to Attach Database USE [master] GO CREATE DATABASE [AdventureWorks2014_new] ON ( FILENAME = 'E:\AdventureWorks2012_Data_new.mdf'), ( FILENAME = 'E:\AdventureWorks2012_log_new.ldf') FOR ATTACH GO Here is the question back to you – Do you still use old methods to attach database? If yes, I suggest that you start using the new method onwards. SQL in Sixty Seconds Video I have attempted to explain the same subject in simple words over in following video. Action Item Here are the blog posts I have previously written on the subject of SA password. You can read it over here: SQL SERVER – 2005 – T-SQL Script to Attach and Detach Database SQL SERVER – Move Database Files MDF and LDF to Another Location SQL SERVER – 2005 Take Off Line or Detach Database SQL SERVER – Attach mdf file without ldf file in Database SQL SERVER – Copy Database from Instance to Another Instance – Copy Paste in SQL Server You can subscribe to my YouTube Channel for frequent updates. Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQLAuthority Book Review, SQLAuthority News, T SQL, Video

Read the article

Function currying in Javascript

- by kerry

Do you catch yourself doing something like this often? 1: Ajax.request('/my/url', {'myParam': paramVal}, function() { myCallback(paramVal); }); Creating a function which calls another function asynchronously is a bad idea because the value of paramVal may change before it is called. Enter the curry function: 1: Function.prototype.curry = function(scope) { 2: var args = []; 3: for (var i=1, len = arguments.length; i < len; ++i) { 4: args.push(arguments[i]); 5: } 6: var m = this; 7: return function() { 8: m.apply(scope, args); 9: }; 10: } This function creates a wrapper around the function and ‘locks in’ the method parameters. The first parameter is the scope of the function call (usually this or window). Any remaining parameters will be passed to the method call. Using the curry method the above call changes to: 1: Ajax.request('/my/url', {'myParam': paramVal}, myCallback.curry(window,paramVal)); Remember when passing objects to the curry method that the objects members may still change.

Read the article

Organizing an entity system with external component managers?

- by Gustav

I'm designing a game engine for a top-down multiplayer 2D shooter game, which I want to be reasonably reuseable for other top-down shooter games. At the moment I'm thinking about how something like an entity system in it should be designed. First I thought about this: I have a class called EntityManager. It should implement a method called Update and another one called Draw. The reason for me separating Logic and Rendering is because then I can omit the Draw method if running a standalone server. EntityManager owns a list of objects of type BaseEntity. Each entity owns a list of components such as EntityModel (the drawable representation of an entity), EntityNetworkInterface, and EntityPhysicalBody. EntityManager also owns a list of component managers like EntityRenderManager, EntityNetworkManager and EntityPhysicsManager. Each component manager keeps references to the entity components. There are various reasons for moving this code out of the entity's own class and do it collectively instead. For example, I'm using an external physics library, Box2D, for the game. In Box2D, you first add the bodies and shapes to a world (owned by the EntityPhysicsManager in this case) and add collision callbacks (which would be dispatched to the entity object itself in my system). Then you run a function which simulates everything in the system. I find it hard to find a better solution to do this than doing it in an external component manager like this. Entity creation is done like this: EntityManager implements the method RegisterEntity(entityClass, factory) which registers how to create an entity if that class. It also implements the method CreateEntity(entityClass) which would return an object of type BaseEntity. Well now comes my problem: How would the reference to a component be registered to the component managers? I have no idea how I would reference the component managers from a factory/closure.

Read the article

Creating Custom HTML Helpers in ASP.NET MVC

- by Shravan

ASP.NET MVC provides many built-in HTML Helpers. With help of HTML Helpers we can reduce the amount of typing of HTML tags for creating a HTML page. For example we use Html.TextBox() helper method it generates html input textbox. Write the following code snippet in MVC View: <%=Html.TextBox("txtName",20)%> It generates the following html in output page: <input id="txtName" name="txtName" type="text" value="20" /> List of built-in HTML Helpers provided by ASP.NET MVC. ActionLink() - Links to an action method. BeginForm() - Marks the start of a form and links to the action method that renders the form. CheckBox() - Renders a check box. DropDownList() - Renders a drop-down list. Hidden() - Embeds information in the form that is not rendered for the user to see. ListBox() - Renders a list box. Password() - Renders a text box for entering a password. RadioButton() - Renders a radio button.TextArea() - Renders a text area (multi-line text box). TextBox () - Renders a text box. How to develop our own Custom HTML Helpers? For developing custom HTML helpers the simplest way is to write an extension method for the HtmlHelper class. See the below code, it builds a custom Image HTML Helper for generating image tag. Read The Remaing Blog Post @ http://theshravan.net/blog/creating-custom-html-helpers-in-asp-net-mvc/

Read the article

Can I save & store a user's submission in a way that proves that the data has not been altered, and that the timestamp is accurate?

- by jt0dd

There are many situations where the validity of the timestamp attached to a certain post (submission of information) might be invaluable for the post owner's legal usage. I'm not looking for a service to achieve this, as requested in this great question, but rather a method for the achievement of such a service. For the legal (in most any law system) authentication of text content and its submission time, the owner of the content would need to prove: that the timestamp itself has not been altered and was accurate to begin with. that the text content linked to the timestamp had not been altered I'd like to know how to achieve this via programming (not a language-specific solution, but rather the methodology behind the solution). Can a timestamp be validated to being accurate to the time that the content was really submitted? Can data be stored in a form that it can be read, but not written to, in a proven way? In other words, can I save & store a user's submission in a way that proves that the data has not been altered, and that the timestamp is accurate? I can't think of any programming method that would make this possible, but I am not the most experienced programmer out there. Based on MidnightLightning's answer to the question I cited, this sort of thing is being done. Clarification: I'm looking for a method (hashing, encryption, etc) that would allow an average guy like me to achieve the desired effect through programming. I'm interested in this subject for the purpose of Defensive Publication. I'd like to learn a method that allows an every-day programmer to pick up his computer, write a program, pass information through it, and say: I created this text at this moment in time, and I can prove it. This means the information should be protected from the programmer who writes the code as well. Perhaps a 3rd party API would be required. I'm ok with that.

Read the article

multi-dimension array problem in RGSS (RPG Maker XP)

- by AzDesign

This is my first day code script in RMXP. I read tutorials, ruby references, etc and I found myself stuck on a weird problem, here is the scenario: I made a custom script to display layered images Create the class, create an instance variable to hold the array, create a simple method to add an element into it, done The draw method (skipped the rest of the code to this part): def draw image = [] index = 0 for i in [email protected] if image.size > 0 index = image.size end image[index] = Sprite.new image[index].bitmap = RPG::Cache.picture(@components[i][0] + '.png') image[index].x = @x + @components[i][1] image[index].y = @y + @components[i][2] image[index].z = @z + @components[i][3] @test =+ 1 end end Create an event that does these script > $layerz = Layerz.new $layerz.configuration[0] = ['root',0,0,1] > $layerz.configuration[1] = ['bark',0,10,2] > $layerz.configuration[2] = ['branch',0,30,3] > $layerz.configuration[3] = ['leaves',0,60,4] $layerz.draw Run, trigger the event and the result : ERROR! Undefined method`[]' for nil:NilClass pointing at this line on draw method : image[index].bitmap = RPG::Cache.picture(@components[i][0] + '.png') THEN, I changed the method like these just for testing: def draw image = [] index = 0 for i in [email protected] if image.size > 0 index = image.size end image[index] = Sprite.new image[index].bitmap = RPG::Cache.picture(@components[0][0] + '.png') image[index].x = @x + @components[0][1] image[index].y = @y + @components[0][2] image[index].z = @z + @components[0][3] @test =+ 1 end I changed the @components[i][0] to @components[0][0] and IT WORKS, but only the root as it not iterates to the next array index Im stuck here, see : > in single level array, @components[0] and @components[i] has no problem > in multi-dimension array, @components[0][0] has no problem BUT > in multi-dimension array, @components[i][0] produce the error as above > mentioned. any suggestion to fix the error ? Or did I wrote something wrong ?

Read the article

Using textureGrad for anisotropic integration approximation

- by Amxx

I'm trying to develop a real time rendering method using real time acquired envmap (cubemap) for lightning. This implies that my envmap can change as often as every frame and I therefore cannot use any method base on precomputation of the envmap (such as convolution with BRDF...) So far my method worked well with Phong BRDF. For specular contribution I direclty read the value in my sampleCube and I use mipmap levels + linear filter for simulating the roughtness of the material considered: int size = textureSize(envmap, 0).x; float specular_level = log2(size * sqrt(3.0)) - 0.5 * log2(ns + 1); vec3 env_specular = ks * specular_color * textureLod(envmap, l_g, specular_level); From this method I would like to upgrade to a microfacet based BRDF. I already have algorithm for evaluating the shape (including anisotropic direction) of the reflection but I cannot manage to read the values I want in my sampleCube. I believe I have to use textureGrad(envmap, l_g, X, Y); with l_g being the reflection direction in global space but I cannot manage to find which values to give to X and Y in order to correctly specify the area I want to consider. What value should I give to X and Y in orther for textureGrad(envmap, l_g, X, Y); to give the same result as textureLod(envmap, l_g, specular_level);

Read the article

C# Adds Optional and Named Arguments

Earlier this month Microsoft released Visual Studio 2010, the .NET Framework 4.0 (which includes ASP.NET 4.0), and new versions of their core programming languages: C# 4.0 and Visual Basic 10. In designing the latest versions of C# and VB, Microsoft has worked to bring the two languages into closer parity. Certain features available in C# were missing in VB, and vice-a-versa. Last week I wrote about Visual Basic 2010's language enhancements, which include implicit line continuation, auto-implemented properties, and collection initializers - three useful features that were available in previous versions of C#. Similarly, C# 4.0 introduces new features to the C# programming language that were available in earlier versions of Visual Basic, namely optional arguments and named arguments. Optional arguments allow developers to specify default values for one or more arguments to a method. When calling such a method, these optional arguments may be omitted, in which case their default value is used. In a nutshell, optional arguments allow for a more terse syntax for method overloading. Named arguments, on the other hand, improve readability by allowing developers to indicate the name of an argument (along with its value) when calling a method. This article examines how to use optional arguments and named arguments in C# 4.0. Read on to learn more! Read More >Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

Read the article

C# Adds Optional and Named Arguments

Earlier this month Microsoft released Visual Studio 2010, the .NET Framework 4.0 (which includes ASP.NET 4.0), and new versions of their core programming languages: C# 4.0 and Visual Basic 10. In designing the latest versions of C# and VB, Microsoft has worked to bring the two languages into closer parity. Certain features available in C# were missing in VB, and vice-a-versa. Last week I wrote about Visual Basic 2010's language enhancements, which include implicit line continuation, auto-implemented properties, and collection initializers - three useful features that were available in previous versions of C#. Similarly, C# 4.0 introduces new features to the C# programming language that were available in earlier versions of Visual Basic, namely optional arguments and named arguments. Optional arguments allow developers to specify default values for one or more arguments to a method. When calling such a method, these optional arguments may be omitted, in which case their default value is used. In a nutshell, optional arguments allow for a more terse syntax for method overloading. Named arguments, on the other hand, improve readability by allowing developers to indicate the name of an argument (along with its value) when calling a method. This article examines how to use optional arguments and named arguments in C# 4.0. Read on to learn more! Read More >

Read the article

how to think like a computer scientist java edition exercise 7.2 [on hold]

- by James Canfield

I cannot figure out how to write this program, can someone please help me?! The purpose of this method is to practice manipulating St rings. Create a new program called Name.java. This program will take a name string consisting of EITHER a first name followed by a last name (nonstandar d format) or a last name followed by a comma then a first name (standard format). Ie . “Joe Smith” vs. “Smith, Joe”. This program will convert the string to standard format if it is not already in standard format. Write a method called hasComma that takes a name as an argument and that returns a boolean indicating whether it contains a comma. If i t does, you can assume that it is in last name first format. You can use the indexOf String m ethod to help you. Write a method called convertName that takes a name as an argument. It should check whether it contains a comma by calling your hasComma method. If it does, it should just return the string. If not, then it should assume th at the name is in first name first format, and it should return a new string that contains the name converted to last name comma first format. Uses charAt, length, substring, and indexOf methods. In your main program, loop, asking the user for a n ame string. If the string is not blank, call convertName and print the results. The loop terminat es when the string is blank. HINTS/SUGGESTIONS: Use the charAt, length, substring, and indexOf Str ing methods. Use scanner for your input. To get the full line, complete with spaces, use reader.nextLine()

Read the article

Detect two specific objects collision with bullet physics

- by sebap123

I have got some problem with defining collision between objects in my game using bullet physics. I know that objects are colliding with each other simultaneously and I don't have to do anything more. However I need to be noticed when one object collides with one of the rest. It is quite awkward written so I will tell what I want to achive. I have got ball which hits wall from tubes. Everything is on the floor. When ball hits wall some fragments fall down to infinity. So I have got bellow floor btStaticPlaneShape. This is place where most of objects is stoping and then I can start another action. But not all of them. So I've been trying to use function checkCollideWith but it isn't good method as it was said in reference and wiki. So I've checked method described in wiki http://bulletphysics.org/mediawiki-1.5.8/index.php/Collision_Callbacks_and_Triggers called contact information. This isn't good method either because it is extremly hard to identify what is what when colliding. You have to also remember that ball is almost all the time colliding with something - floor, wall or eart level. So is there any other method to check what is colliding with what?

Read the article

What is the structure of network managers system-connections files?

- by Oyks Livede

could anyone list the complete structure of the configuration files, which network manager stores for known networks in /etc/NetworkManager/system-connections for known networks? Sample (filename askUbuntu): [connection] id=askUbuntu uuid=81255b2e-bdf1-4bdb-b6f5-b94ef16550cd type=802-11-wireless [802-11-wireless] ssid=askUbuntu mode=infrastructure mac-address=00:08:CA:E6:76:D8 [ipv6] method=auto [ipv4] method=auto I would like to create some of them by my own using a script. However, before doing so I would like to know every possible option. Furthermore, this structure seems somehow to resemble the information you can get using the dbus for active connections. dbus-send --system --print-reply \ --dest=org.freedesktop.NetworkManager \ "$active_setting_path" \ # /org/freedesktop/NetworkManager/Settings/2 org.freedesktop.NetworkManager.Settings.Connection.GetSettings Will tell you: array [ dict entry( string "802-11-wireless" array [ dict entry( string "ssid" variant array of bytes "askUbuntu" ) dict entry( string "mode" variant string "infrastructure" ) dict entry( string "mac-address" variant array of bytes [ 00 08 ca e6 76 d8 ] ) dict entry( string "seen-bssids" variant array [ string "02:1A:11:F8:C5:64" string "02:1A:11:FD:1F:EA" ] ) ] ) dict entry( string "connection" array [ dict entry( string "id" variant string "askUbuntu" ) dict entry( string "uuid" variant string "81255b2e-bdf1-4bdb-b6f5-b94ef16550cd" ) dict entry( string "timestamp" variant uint64 1383146668 ) dict entry( string "type" variant string "802-11-wireless" ) ] ) dict entry( string "ipv4" array [ dict entry( string "addresses" variant array [ ] ) dict entry( string "dns" variant array [ ] ) dict entry( string "method" variant string "auto" ) dict entry( string "routes" variant array [ ] ) ] ) dict entry( string "ipv6" array [ dict entry( string "addresses" variant array [ ] ) dict entry( string "dns" variant array [ ] ) dict entry( string "method" variant string "auto" ) dict entry( string "routes" variant array [ ] ) ] ) ] I can create new setting files using the dbus (AddSettings() in /org/freedesktop/NetworkManager/Settings) passing this type of input, so explaining me this structure and telling me all possible options will also help. Afaik, this is a Dictionary{String, Dictionary{String, Variant}}. Will there be any difference creating config files directly or using the dbus?

Read the article

C#/.NET Little Wonders: Use Cast() and TypeOf() to Change Sequence Type

- by James Michael Hare

Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. We’ve seen how the Select() extension method lets you project a sequence from one type to a new type which is handy for getting just parts of items, or building new items. But what happens when the items in the sequence are already the type you want, but the sequence itself is typed to an interface or super-type instead of the sub-type you need? For example, you may have a sequence of Rectangle stored in an IEnumerable<Shape> and want to consider it an IEnumerable<Rectangle> sequence instead. Today we’ll look at two handy extension methods, Cast<TResult>() and OfType<TResult>() which help you with this task. Cast<TResult>() – Attempt to cast all items to type TResult So, the first thing we can do would be to attempt to create a sequence of TResult from every item in the source sequence. Typically we’d do this if we had an IEnumerable<T> where we knew that every item was actually a TResult where TResult inherits/implements T. For example, assume the typical Shape example classes: 1: // abstract base class 2: public abstract class Shape { } 3: 4: // a basic rectangle 5: public class Rectangle : Shape 6: { 7: public int Widtgh { get; set; } 8: public int Height { get; set; } 9: } And let’s assume we have a sequence of Shape where every Shape is a Rectangle… 1: var shapes = new List<Shape> 2: { 3: new Rectangle { Width = 3, Height = 5 }, 4: new Rectangle { Width = 10, Height = 13 }, 5: // ... 6: }; To get the sequence of Shape as a sequence of Rectangle, of course, we could use a Select() clause, such as: 1: // select each Shape, cast it to Rectangle 2: var rectangles = shapes 3: .Select(s => (Rectangle)s) 4: .ToList(); But that’s a bit verbose, and fortunately there is already a facility built in and ready to use in the form of the Cast<TResult>() extension method: 1: // cast each item to Rectangle and store in a List<Rectangle> 2: var rectangles = shapes 3: .Cast<Rectangle>() 4: .ToList(); However, we should note that if anything in the list cannot be cast to a Rectangle, you will get an InvalidCastException thrown at runtime. Thus, if our Shape sequence had a Circle in it, the call to Cast<Rectangle>() would have failed. As such, you should only do this when you are reasonably sure of what the sequence actually contains (or are willing to handle an exception if you’re wrong). Another handy use of Cast<TResult>() is using it to convert an IEnumerable to an IEnumerable<T>. If you look at the signature, you’ll see that the Cast<TResult>() extension method actually extends the older, object-based IEnumerable interface instead of the newer, generic IEnumerable<T>. This is your gateway method for being able to use LINQ on older, non-generic sequences. For example, consider the following: 1: // the older, non-generic collections are sequence of object 2: var shapes = new ArrayList 3: { 4: new Rectangle { Width = 3, Height = 13 }, 5: new Rectangle { Width = 10, Height = 20 }, 6: // ... 7: }; Since this is an older, object based collection, we cannot use the LINQ extension methods on it directly. For example, if I wanted to query the Shape sequence for only those Rectangles whose Width is > 5, I can’t do this: 1: // compiler error, Where() operates on IEnumerable<T>, not IEnumerable 2: var bigRectangles = shapes.Where(r => r.Width > 5); However, I can use Cast<Rectangle>() to treat my ArrayList as an IEnumerable<Rectangle> and then do the query! 1: // ah, that’s better! 2: var bigRectangles = shapes.Cast<Rectangle>().Where(r => r.Width > 5); Or, if you prefer, in LINQ query expression syntax: 1: var bigRectangles = from s in shapes.Cast<Rectangle>() 2: where s.Width > 5 3: select s; One quick warning: Cast<TResult>() only attempts to cast, it won’t perform a cast conversion. That is, consider this: 1: var intList = new List<int> { 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89 }; 2: 3: // casting ints to longs, this should work, right? 4: var asLong = intList.Cast<long>().ToList(); Will the code above work? No, you’ll get a InvalidCastException. Remember that Cast<TResult>() is an extension of IEnumerable, thus it is a sequence of object, which means that it will box every int as an object as it enumerates over it, and there is no cast conversion from object to long, and thus the cast fails. In other words, a cast from int to long will succeed because there is a conversion from int to long. But a cast from int to object to long will not, because you can only unbox an item by casting it to its exact type. For more information on why cast-converting boxed values doesn’t work, see this post on The Dangers of Casting Boxed Values (here). OfType<TResult>() – Filter sequence to only items of type TResult So, we’ve seen how we can use Cast<TResult>() to change the type of our sequence, when we expect all the items of the sequence to be of a specific type. But what do we do when a sequence contains many different types, and we are only concerned with a subset of a given type? For example, what if a sequence of Shape contains Rectangle and Circle instances, and we just want to select all of the Rectangle instances? Well, let’s say we had this sequence of Shape: 1: var shapes = new List<Shape> 2: { 3: new Rectangle { Width = 3, Height = 5 }, 4: new Rectangle { Width = 10, Height = 13 }, 5: new Circle { Radius = 10 }, 6: new Square { Side = 13 }, 7: // ... 8: }; Well, we could get the rectangles using Select(), like: 1: var onlyRectangles = shapes.Where(s => s is Rectangle).ToList(); But fortunately, an easier way has already been written for us in the form of the OfType<T>() extension method: 1: // returns only a sequence of the shapes that are Rectangles 2: var onlyRectangles = shapes.OfType<Rectangle>().ToList(); Now we have a sequence of only the Rectangles in the original sequence, we can also use this to chain other queries that depend on Rectangles, such as: 1: // select only Rectangles, then filter to only those more than 2: // 5 units wide... 3: var onlyBigRectangles = shapes.OfType<Rectangle>() 4: .Where(r => r.Width > 5) 5: .ToList(); The OfType<Rectangle>() will filter the sequence to only the items that are of type Rectangle (or a subclass of it), and that results in an IEnumerable<Rectangle>, we can then apply the other LINQ extension methods to query that list further. Just as Cast<TResult>() is an extension method on IEnumerable (and not IEnumerable<T>), the same is true for OfType<T>(). This means that you can use OfType<TResult>() on object-based collections as well. For example, given an ArrayList containing Shapes, as below: 1: // object-based collections are a sequence of object 2: var shapes = new ArrayList 3: { 4: new Rectangle { Width = 3, Height = 5 }, 5: new Rectangle { Width = 10, Height = 13 }, 6: new Circle { Radius = 10 }, 7: new Square { Side = 13 }, 8: // ... 9: }; We can use OfType<Rectangle> to filter the sequence to only Rectangle items (and subclasses), and then chain other LINQ expressions, since we will then be of type IEnumerable<Rectangle>: 1: // OfType() converts the sequence of object to a new sequence 2: // containing only Rectangle or sub-types of Rectangle. 3: var onlyBigRectangles = shapes.OfType<Rectangle>() 4: .Where(r => r.Width > 5) 5: .ToList(); Summary So now we’ve seen two different ways to get a sequence of a superclass or interface down to a more specific sequence of a subclass or implementation. The Cast<TResult>() method casts every item in the source sequence to type TResult, and the OfType<TResult>() method selects only those items in the source sequence that are of type TResult. You can use these to downcast sequences, or adapt older types and sequences that only implement IEnumerable (such as DataTable, ArrayList, etc.). Technorati Tags: C#,CSharp,.NET,LINQ,Little Wonders,TypeOf,Cast,IEnumerable<T>

Read the article

Should one always know what an API is doing just by looking at the code?

- by markmnl

Recently I have been developing my own API and with that invested interest in API design I have been keenly interested how I can improve my API design. One aspect that has come up a couple times is (not by users of my API but in my observing discussion about the topic): one should know just by looking at the code calling the API what it is doing. For example see this discussion on GitHub for the discourse repo, it goes something like: foo.update_pinned(true, true); Just by looking at the code (without knowing the parameter names, documentation etc.) one cannot guess what it is going to do - what does the 2nd argument mean? The suggested improvement is to have something like: foo.pin() foo.unpin() foo.pin_globally() And that clears things up (the 2nd arg was whether to pin foo globally, I am guessing), and I agree in this case the later would certainly be an improvement. However I believe there can be instances where methods to set different but logically related state would be better exposed as one method call rather than separate ones, even though you would not know what it is doing just by looking at the code. (So you would have to resort to looking at the parameter names and documentation to find out - which personally I would always do no matter what if I am unfamiliar with an API). For example I expose one method SetVisibility(bool, string, bool) on a FalconPeer and I acknowledge just looking at the line: falconPeer.SetVisibility(true, "aerw3", true); You would have no idea what it is doing. It is setting 3 different values that control the "visibility" of the falconPeer in the logical sense: accept join requests, only with password and reply to discovery requests. Splitting this out into 3 method calls could lead to a user of the API to set one aspect of "visibility" forgetting to set others that I force them to think about by only exposing the one method to set all aspects of "visibility". Furthermore when the user wants to change one aspect they almost always will want to change another aspect and can now do so in one call.

Read the article

Should these concerns be separated into separate objects?

- by Lewis Bassett

I have objects which implement the interface BroadcastInterface, which represents a message that is to be broadcast to all users of a particular group. It has a setter and getter method for the Subject and Body properties, and an addRecipientRole() method, which takes a given role and finds the contact token (e.g., an email address) for each user in the role and stores it. It then has a getContactTokens() method. BroadcastInterface objects are passed to an object that implements BroadcasterInterface. These objects are responsible for broadcasting a passed BroadcastInterface object. For example, an EmailBroadcaster implementation of the BroadcasterInterface will take EmailBroadcast objects and use the mailer services to email them out. Now, depending on what BroadcasterInterface implementation is used to broadcast, a different implementation of BroadcastInterface is used by client code. The Single Responsibility Principle seems to suggest that I should have a separate BroadcastFactory object, for creating BroadcastInterface objects, depending on what BroadcasterInterface implementation is used, as creating the BroadcastInterface object is a different responsibility to broadcasting them. But the class used for creating BroadcastInterface objects depends on what implementation of BroadcasterInterface is used to broadcast them. I think, because the knowledge of what method is used to send the broadcasts should only be configured once, the BroadcasterInterface object should be responsible for providing new BroadcastInterface objects. Does the responsibility of “creating and broadcasting objects that implement the BroadcastInterface interface” violate the Single Responsibility Principle? (Because the contact token for sending the broadcast out to the users will differ depending on the way it is broadcasted, I need different broadcast classes—though client code will not be able to tell the difference.)

Read the article

Silverlight 4 Twitter Client – Part 6

- by Max

In this post, we are going to look into implementing lists into our twitter application and also about enhancing the data grid to display the status messages in a pleasing way with the profile images. Twitter lists are really cool feature that they recently added, I love them and I’ve quite a few lists setup one for DOTNET gurus, SQL Server gurus and one for a few celebrities. You can follow them here. Now let us move onto our tutorial. 1) Lists can be subscribed to in two ways, one can be user’s own lists, which he has created and another one is the lists that the user is following. Like for example, I’ve created 3 lists myself and I am following 1 other lists created by another user. Both of them cannot be fetched in the same api call, its a two step process. 2) In the TwitterCredentialsSubmit method we’ve in Home.xaml.cs, let us do the first api call to get the lists that the user has created. For this the call has to be made to https://twitter.com/<TwitterUsername>/lists.xml. The API reference is available here. myService1.AllowReadStreamBuffering = true; myService1.UseDefaultCredentials = false; myService1.Credentials = new NetworkCredential(GlobalVariable.getUserName(), GlobalVariable.getPassword()); myService1.DownloadStringCompleted += new DownloadStringCompletedEventHandler(ListsRequestCompleted); myService1.DownloadStringAsync(new Uri("https://twitter.com/" + GlobalVariable.getUserName() + "/lists.xml")); 3) Now let us look at implementing the event handler – ListRequestCompleted for this. public void ListsRequestCompleted(object sender, System.Net.DownloadStringCompletedEventArgs e) { if (e.Error != null) { StatusMessage.Text = "This application must be installed first."; parseXML(""); } else { //MessageBox.Show(e.Result.ToString()); parseXMLLists(e.Result.ToString()); } } 4) Now let us look at the parseXMLLists in detail xdoc = XDocument.Parse(text); var answer = (from status in xdoc.Descendants("list") select status.Element("name").Value); foreach (var p in answer) { Border bord = new Border(); bord.CornerRadius = new CornerRadius(10, 10, 10, 10); Button b = new Button(); b.MinWidth = 70; b.Background = new SolidColorBrush(Colors.Black); b.Foreground = new SolidColorBrush(Colors.Black); //b.Width = 70; b.Height = 25; b.Click += new RoutedEventHandler(b_Click); b.Content = p.ToString(); bord.Child = b; TwitterListStack.Children.Add(bord); } So here what am I doing, I am just dynamically creating a button for each of the lists and put them within a StackPanel and for each of these buttons, I am creating a event handler b_Click which will be fired on button click. We will look into this method in detail soon. For now let us get the buttons displayed. 5) Now the user might have some lists to which he has subscribed to. We need to create a button for these as well. In the end of TwitterCredentialsSubmit method, we need to make a call to http://api.twitter.com/1/<TwitterUsername>/lists/subscriptions.xml. Reference is available here. The code will look like this below. myService2.AllowReadStreamBuffering = true; myService2.UseDefaultCredentials = false; myService2.Credentials = new NetworkCredential(GlobalVariable.getUserName(), GlobalVariable.getPassword()); myService2.DownloadStringCompleted += new DownloadStringCompletedEventHandler(ListsSubsRequestCompleted); myService2.DownloadStringAsync(new Uri("http://api.twitter.com/1/" + GlobalVariable.getUserName() + "/lists/subscriptions.xml")); 6) In the event handler – ListsSubsRequestCompleted, we need to parse through the xml string and create a button for each of the lists subscribed, let us see how. I’ve taken only the “full_name”, you can choose what you want, refer the documentation here. Note the point that the full_name will have @<UserName>/<ListName> format – this will be useful very soon. xdoc = XDocument.Parse(text); var answer = (from status in xdoc.Descendants("list") select status.Element("full_name").Value); foreach (var p in answer) { Border bord = new Border(); bord.CornerRadius = new CornerRadius(10, 10, 10, 10); Button b = new Button(); b.Background = new SolidColorBrush(Colors.Black); b.Foreground = new SolidColorBrush(Colors.Black); //b.Width = 70; b.MinWidth = 70; b.Height = 25; b.Click += new RoutedEventHandler(b_Click); b.Content = p.ToString(); bord.Child = b; TwitterListStack.Children.Add(bord); } Please note, I am setting the button width to be auto based on the content and also giving it a midwidth value. I wanted to create a rounded corner buttons, but for some reason its not working. Also add this StackPanel – TwitterListStack of the Home.xaml <StackPanel HorizontalAlignment="Center" Orientation="Horizontal" Name="TwitterListStack"></StackPanel> After doing this, you would get a series of buttons in the top of the home page. 7) Now the button click event handler – b_Click, in this method, once the button is clicked, I call another method with the content string of the button which is clicked as the parameter. Button b = (Button)e.OriginalSource; getListStatuses(b.Content.ToString()); 8) Now the getListsStatuses method: toggleProgressBar(true); WebRequest.RegisterPrefix("http://", System.Net.Browser.WebRequestCreator.ClientHttp); WebClient myService = new WebClient(); myService.AllowReadStreamBuffering = true; myService.UseDefaultCredentials = false; myService.DownloadStringCompleted += new DownloadStringCompletedEventHandler(TimelineRequestCompleted); if (listName.IndexOf("@") > -1 && listName.IndexOf("/") > -1) { string[] arrays = null; arrays = listName.Split('/'); arrays[0] = arrays[0].Replace("@", " ").Trim(); //MessageBox.Show(arrays[0]); //MessageBox.Show(arrays[1]); string url = "http://api.twitter.com/1/" + arrays[0] + "/lists/" + arrays[1] + "/statuses.xml"; //MessageBox.Show(url); myService.DownloadStringAsync(new Uri(url)); } else myService.DownloadStringAsync(new Uri("http://api.twitter.com/1/" + GlobalVariable.getUserName() + "/lists/" + listName + "/statuses.xml")); Please note that the url to look at will be different based on the list clicked – if its user created, the url format will be http://api.twitter.com/1/<CurentUser>/lists/<ListName>/statuses.xml But if it is some lists subscribed, it will be http://api.twitter.com/1/<ListOwnerUserName>/lists/<ListName>/statuses.xml The first one is pretty straight forward to implement, but if its a list subscribed, we need to split the listName string to get the list owner and list name and user them to form the string. So that is what I’ve done in this method, if the listName has got “@” and “/” I build the url differently. 9) Until now, we’ve been using only a few nodes of the status message xml string, now we will look to fetch a new field - “profile_image_url”. Images in datagrid – COOL. So for that, we need to modify our Status.cs file to include two more fields one string another BitmapImage with get and set. public string profile_image_url { get; set; } public BitmapImage profileImage { get; set; } 10) Now let us change the generic parseXML method which is used for binding to the datagrid. public void parseXML(string text) { XDocument xdoc; xdoc = XDocument.Parse(text); statusList = new List<Status>(); statusList = (from status in xdoc.Descendants("status") select new Status { ID = status.Element("id").Value, Text = status.Element("text").Value, Source = status.Element("source").Value, UserID = status.Element("user").Element("id").Value, UserName = status.Element("user").Element("screen_name").Value, profile_image_url = status.Element("user").Element("profile_image_url").Value, profileImage = new BitmapImage(new Uri(status.Element("user").Element("profile_image_url").Value)) }).ToList(); DataGridStatus.ItemsSource = statusList; StatusMessage.Text = "Datagrid refreshed."; toggleProgressBar(false); } We are here creating a new bitmap image from the image url and creating a new Status object for every status and binding them to the data grid. Refer to the Twitter API documentation here. You can choose any column you want. 11) Until now, we’ve been using the auto generate columns for the data grid, but if you want it to be really cool, you need to define the columns with templates, etc… <data:DataGrid AutoGenerateColumns="False" Name="DataGridStatus" Height="Auto" MinWidth="400"> <data:DataGrid.Columns> <data:DataGridTemplateColumn Width="50" Header=""> <data:DataGridTemplateColumn.CellTemplate> <DataTemplate> <Image Source="{Binding profileImage}" Width="50" Height="50" Margin="1"/> </DataTemplate> </data:DataGridTemplateColumn.CellTemplate> </data:DataGridTemplateColumn> <data:DataGridTextColumn Width="Auto" Header="User Name" Binding="{Binding UserName}" /> <data:DataGridTemplateColumn MinWidth="300" Width="Auto" Header="Status"> <data:DataGridTemplateColumn.CellTemplate> <DataTemplate> <TextBlock TextWrapping="Wrap" Text="{Binding Text}"/> </DataTemplate> </data:DataGridTemplateColumn.CellTemplate> </data:DataGridTemplateColumn> </data:DataGrid.Columns> </data:DataGrid> I’ve used only three columns – Profile image, Username, Status text. Now our Datagrid will look super cool like this. Coincidentally, Tim Heuer is on the screenshot , who is a Silverlight Guru and works on SL team in Microsoft. His blog is really super. Here is the zipped file for all the xaml, xaml.cs & class files pages. Ok let us stop here for now, will look into implementing few more features in the next few posts and then I am going to look into developing a ASP.NET MVC 2 application. Hope you all liked this post. If you have any queries / suggestions feel free to comment below or contact me. Cheers! Technorati Tags: Silverlight,LINQ,Twitter API,Twitter,Silverlight 4

Search Results

Search found 32130 results on 1286 pages for 'method chaining'.

Page 187/1286 | < Previous Page | 183 184 185 186 187 188 189 190 191 192 193 194 | Next Page >

- by imran_ku07

- by Stephen Walther

- by psheriff

- by Reed

- by Reed

- by nmarun

- by James Michael Hare

- by SAMIR BHOGAYTA

- by dwahlin

- by Pinal Dave

- by kerry

- by Gustav

- by Shravan

- by jt0dd

- by AzDesign

- by Amxx

- by James Canfield

- by sebap123

- by Oyks Livede

- by James Michael Hare

- by markmnl

- by Lewis Bassett

- by Max

< Previous Page | 183 184 185 186 187 188 189 190 191 192 193 194 | Next Page >