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• Is there a Twitter Bootstrap class that means "initially hidden"?

  - by bgp

  Using Bootstrap 3, I have an element on a page I want to show later in response to the user clicking a button. Example: <div id="search_results"> ... gets populated from ajax data later ... </div> <button id="search_button" type="button" class="btn btn-primary pull-right">Search</button> <script> $('#search_button').click(function() { // ... do the call to search // and in the callback: $('#search_results').show(); }); </script> The search_results div should be initially hidden. Is there some normal/best practice way of doing this with bootstrap? Yes, I do realize I can just put style="display:none" on search_results, but is that the best way to do it? It would seem to be a bit better to have a style that semantically means "initially hidden". (NOTE: The hidden or hide classes don't do this as they are !important and show(), toggle(), etc. use an inline style which does not override them, i.e. setting "hidden" as the class makes it unshowable from jQuery.)

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• Avoiding instanceof in Java

  - by Mark Lutton

  Having a chain of "instanceof" operations is considered a "code smell". The standard answer is "use polymorphism". How would I do it in this case? There are a number of subclasses of a base class; none of them are under my control. An analogous situation would be with the Java classes Integer, Double, BigDecimal etc. if (obj instanceof Integer) {NumberStuff.handle((Integer)obj);} else if (obj instanceof BigDecimal) {BigDecimalStuff.handle((BigDecimal)obj);} else if (obj instanceof Double) {DoubleStuff.handle((Double)obj);} I do have control over NumberStuff and so on. I don't want to use many lines of code where a few lines would do. (Sometimes I make a HashMap mapping Integer.class to an instance of IntegerStuff, BigDecimal.class to an instance of BigDecimalStuff etc. But today I want something simpler.) I'd like something as simple as this: public static handle(Integer num) { ... } public static handle(BigDecimal num) { ... } But Java just doesn't work that way. I'd like to use static methods when formatting. The things I'm formatting are composite, where a Thing1 can contain an array Thing2s and a Thing2 can contain an array of Thing1s. I had a problem when I implemented my formatters like this: class Thing1Formatter { private static Thing2Formatter thing2Formatter = new Thing2Formatter(); public format(Thing thing) { thing2Formatter.format(thing.innerThing2); } } class Thing2Formatter { private static Thing1Formatter thing1Formatter = new Thing1Formatter(); public format(Thing2 thing) { thing1Formatter.format(thing.innerThing1); } } Yes, I know the HashMap and a bit more code can fix that too. But the "instanceof" seems so readable and maintainable by comparison. Is there anything simple but not smelly?

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• Overload the behavior of count() when called on certain objects

  - by Tom

  In PHP 5, you can use magic methods, overload some classes, etc. In C++, you can implement functions that exist is STL as long as the argument types are different. Is there a way to do this in PHP? An example of what I'd like to do is this: class a { function a() { $this->list = array("1", "2"); } } $blah = new a(); count($blah); I would like blah to return 2. IE count the values of a specific array in the class. So in C++, the way I would do this might look like this: int count(a varName) { return count(varName->list); } Basically, I am trying to simplify data calls for a large application so I can call do this: count($object); rather than count($object->list); The list is going to be potentially a list of objects so depending on how it's used, it could be really nasty statement if someone has to do it the current way: count($object->list[0]->list[0]->list); So, can I make something similar to this: function count(a $object) { count($object->list); } I know PHP's count accepts a mixed var, so I don't know if I can override an individual type.

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• OOP beginner: classB extends classA. classA already object. method in classB needed.. etc.

  - by Yvo

  Hey guys, I'm learning myself to go from function based PHP coding to OOP. And this is the situation: ClassA holds many basic tool methods (functions). it's __construct makes a DB connection. ClassB holds specific methods based on a certain activity (extract widgets). ClassB extends ClassA because it uses some of the basic tools in there e.g. a database call. In a php file I create a $a_class = new ClassA object (thus a new DB connection). Now I need a method in ClassB. I do $b_class = new ClassB; and call a method, which uses a method from it's parent:: ClassA. In this example, i'm having ClassA 'used' twice. Onces as object, and onces via a parent:: call, so ClassA creates another DB connection (or not?). So what is the best setup for this basic classes parent, child (extend) situation? I only want to make one connection of course? I don't like to forward the object to ClassB like this $b_class = new ClassB($a_object); or is that the best way? Thanks for thinking with me, and helping :d

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• Why does Java think my object is a variable?

  - by user2896898

  Ok so I'm trying to make a simple pong game. I have a paddle that follows the mouse and a ball that bounces around. I wrote a method collidesWith(Sprite s) inside of my Sprite class that checks if the ball collides with the paddle (this works and isn't the problem). I have two objects extending my sprite class, a ball and a paddle object. So inside of my ball class I'm trying to check if it collides with the paddle. So I've tried if(this.collidesWith(paddle) == true){ System.out.println("They touched"); } I've also tried ball.collidesWith(paddle) and other combinations but it always says the same thing about the paddle (and the ball when I use ball.collidesWith) "Cannot find symbol. Symbol: variable paddle(or ball). Location: class Ball" So if I'm reading this right, it thinks that the paddle (and ball) are variables and it's complaining because it can't find them. How can I make it understand I am passing in objects, not variables? For extra information, an earlier assignment had me make two boxes and for them to change colors when they were colliding. In that assignment I used very similar code to above with if(boxOne.collidesWith(boxTwo) == true){ System.out.println("yes"); } And in this code it worked just fine. The program knew that boxOne and boxTwo were child classes of my Sprite class. Anyone know why they wouldn't work the same?

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• Mutate an object into an instance of one its subclasses

  - by Gohu

  Hi, Is it possible to mutate an object into an instance of a derived class of the initial's object class? Something like: class Base(): def __init__(self): self.a = 1 def mutate(self): self = Derived() class Derived(Base): def __init__(self): self.b = 2 But that doesn't work. >>> obj = Base() >>> obj.mutate() >>> obj.a 1 >>> obj.b AttributeError... If this isn't possible, how should I do otherwise? My problem is the following: My Base class is like a "summary", and the Derived class is the "whole thing". Of course getting the "whole thing" is a bit expensive so working on summaries as long as it is possible is the point of having these two classes. But you should be able to get it if you want, and then there's no point in having the summary anymore, so every reference to the summary should now be (or contain, at least) the whole thing. I guess I would have to create a class that can hold both, right? class Thing(): def __init__(self): self.summary = Summary() self.whole = None def get_whole_thing(self): self.whole = Whole()

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• Basic Ajax Cache Issue

  - by michaelespinosa

  I have a single page that I need to on occasion asynchronously check the server to see if the status of the page is current (basically, Live or Offline). You will see I have a function with a var live that is set when the page initially loads. I then do an ajax request to the server to retrieve whether the status of live is true or false. I compare the initial live variable with the newly returned data json object. If they're the same I do nothing, but if there different I apply some css classes. I recursively run it with setTimeout (Is there a better way to recursively do this?). My Problem: data.live doesn't change from it's initial time it runs even when it has changed in the db. I know my mysql is working because it returs the right value on the initial load. It seems like a caching issue. Any help is greatly appreciated. function checkLive() { var live = <?=$result["live"]?>; $.ajax({ type: 'get', url: '/live/live.php', dataType: 'json', success: function(data) { console.log('checking for updates... current:' + data.live); if (data.live == live) { return; } else { var elems = $('div.player_meta, object, h3.offline_message'); if (data.live == '1') { elems.removeClass('offline').addClass('live'); } else { elems.addClass('live').addClass('offline'); } } } }); setTimeout(function() { checkLive() } ,15000); } checkLive();

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• What does this Java generics paradigm do and what is it called?

  - by Tom

  I'm looking at some Java classes that have the following form: public abstract class A <E extends A<E>> implements Comparable <E> { public final int compareTo( E other ) { // etc } } public class B extends A <B> { // etc } public class C extends A <C> { // etc } My usage of "Comparable" here is just to illustrate a possible use of the generic parameter "E". Does this usage of generics/inheritance have a name? What is it used for? My impression is that this allows the abstract class to provide a common implementation of a method (such as compareTo) without having to provide it in the subclasses. However, in this example, unlike an inherited method it would restrict subclasses to invoking compareTo on other instances of the same subclass, rather than any "A" subclass. Does this sound right? Anyway, just curious if any gurus out there have seen this before and know what it does. Thanks!

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• Why does java.util.concurrent.ArrayBlockingQueue use 'while' loops instead of 'if' around calls to

  - by theFunkyEngineer

  I have been playing with my own version of this, using 'if', and all seems to be working fine. Of course this will break down horribly if signalAll() is used instead of signal(), but if only one thread at a time is notified, how can this go wrong? Their code here - check out the put() and take() methods; a simpler and more-to-the-point implementation can be seen at the top of the JavaDoc for Condition. Relevant portion of my implementation below. public Object get() { lock.lock(); try { if( items.size() < 1 ) hasItems.await(); Object poppedValue = items.getLast(); items.removeLast(); hasSpace.signal(); return poppedValue; } catch (InterruptedException e) { e.printStackTrace(); return null; } finally { lock.unlock(); } } public void put(Object item) { lock.lock(); try { if( items.size() >= capacity ) hasSpace.await(); items.addFirst(item); hasItems.signal(); return; } catch (InterruptedException e) { e.printStackTrace(); } finally { lock.unlock(); } } P.S. I know that generally, particularly in lib classes like this, one should let the exceptions percolate up.

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• Calling a constructor from method within the same class

  - by Nathan

  I'm new to java and I'm learning about creating object classes. One of my homework assignment requires that I call the constructor at least once within a method of the same object class. I'm getting an error that says The method DoubleMatrix(double[][]) is undefined for the type DoubleMatrix Here's my constructor: public DoubleMatrix(double[][] tempArray) { // Declaration int flag = 0; int cnt; // Statement // check to see if doubArray isn't null and has more than 0 rows if(tempArray == null || tempArray.length < 0) { flag++; } // check to see if each row has the same length if(flag == 0) { for(cnt = 0; cnt <= tempArray.length - 1 || flag != 1; cnt++) { if(tempArray[cnt + 1].length != tempArray[0].length) { flag++; } } } else if(flag == 1) { makeDoubMatrix(1, 1);// call makeDoubMatrix method } }// end constructor 2 Here's the method where I try and call the constructor: public double[][] addMatrix(double[][] tempDoub) { // Declaration double[][] newMatrix; int rCnt, cCnt; //Statement // checking to see if both are of same dimension if(doubMatrix.length == tempDoub.length && doubMatrix[0].length == tempDoub[0].length) { newMatrix = new double[doubMatrix.length][doubMatrix[0].length]; // for loop to add matrix to a new one for(rCnt = 0; rCnt <= doubMatrix.length; rCnt++) { for(cCnt = 0; cCnt <= doubMatrix.length; cCnt++) { newMatrix[rCnt][cCnt] = doubMatrix[rCnt][cCnt] + tempDoub[rCnt][cCnt]; } } } else { newMatrix = new double[0][0]; DoubleMatrix(newMatrix) } return newMatrix; }// end addMatrix method Can someone point me to the right direction and explain why I'm getting an error?

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• Open Source Licenses, which one?

  - by sam

  recently I created a java class " Custom Layout Manager ", which I want to make it open-source and distribute it. So it's not really a "product", nor a "complete program". Here's the list of permissions and specifications: You are free to use and modify with some limitations (packages and classes names, should remain the same, if you want another name, extend this class. - The .jar file, project name is ok to change). You don't need to share your modifications. You can't modify and then sell it to others. You can use it as part of your commercial software (For example: It's OK if: you created an instant messaging program, that uses my "Layout", since your "core bussiness" isn't the "Layout", but the msg program. It's NOT OK if: you created another "Layout" by extending it, added some features and sell it.) You can't remove the author's name nor the author's website address. You are free to donate. :D Basically, it's free and it's Ok as you give me credits and don't make money with it. I guess it might be a little bit complex, since you use it "commercially" but cannot sell it separately. I have seeked almost all the licenses, and the closest one was MIT license, but it says that you can sell it, so I don't really want to use this one. Is there any license that fits all these permissions I stated? Thanks.

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• Generating an identifier for objects so that they can be added to a hashtable I have created

  - by dukenukem

  I have a hashtable base class and I am creating different type of hashtable by deriving from it. I only allow it to accept objects that implement my IHashable interface.For example - class LinearProbingHashTable<T> : HashTableBase<T> where T: IHashable { ... ... ... } interface IHashable { /** * Every IHashable implementation should provide an indentfying value for use in generating a hash key. */ int getIdentifier(); } class Car : IHashable { public String Make { get; set; } public String Model { get; set; } public String Color { get; set; } public int Year { get; set; } public int getIdentifier() { /// ??? } } Can anyone suggest a good method for generating an identifier for the car that can be used by the hash function to place it in the hash table? I am actually really looking for a general purpose solution to generating an id for any given class. I would like to have a base class for all classes, HashableObject, that implements IHashable and its getIdentifier method. So then I could just derive from HashableObject which would automatically provide an identifier for any instances. Which means I wouldn't have to write a different getIdentifier method for every object I add to the hashtable. public class HashableObject : IHashable { public int getIdentifier() { // Looking for code here that would generate an id for any object... } } public class Dog : HashableObject { // Dont need to implement getIdentifier because the parent class does it for me }

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• Remove .img css from prepended div

  - by Ivan Schrecklich

  OK as the title says I've got a div which is prepended and dynamically loaded. The problem I have is that I can't split the css on this one as it parses also whole strings. The usage is like that: I've got a @username somewhere in the string. If the user hovers it a div with informations will get prepended to the current username. Now there is the problem that I've allowed users to post images in this text also. As the autolinker is flexible it doesn't know the image sizes and restrictions and I want to leave it like that! So I define css classes which look like that: .minpost img{ max-height: 30px; max-width: 30px; } Of course I don't need to mention that this attribute is also inherited by the prepended div. And that I don't want to! nifty little tricks like !important won't work for me. So I am asking you guys. If you need further informations just ask?!

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• What's New in ASP.NET 4

  - by Navaneeth

  The .NET Framework version 4 includes enhancements for ASP.NET 4 in targeted areas. Visual Studio 2010 and Microsoft Visual Web Developer Express also include enhancements and new features for improved Web development. This document provides an overview of many of the new features that are included in the upcoming release. This topic contains the following sections: ASP.NET Core Services ASP.NET Web Forms ASP.NET MVC Dynamic Data ASP.NET Chart Control Visual Web Developer Enhancements Web Application Deployment with Visual Studio 2010 Enhancements to ASP.NET Multi-Targeting ASP.NET Core Services ASP.NET 4 introduces many features that improve core ASP.NET services such as output caching and session state storage. Extensible Output Caching Since the time that ASP.NET 1.0 was released, output caching has enabled developers to store the generated output of pages, controls, and HTTP responses in memory. On subsequent Web requests, ASP.NET can serve content more quickly by retrieving the generated output from memory instead of regenerating the output from scratch. However, this approach has a limitation — generated content always has to be stored in memory. On servers that experience heavy traffic, the memory requirements for output caching can compete with memory requirements for other parts of a Web application. ASP.NET 4 adds extensibility to output caching that enables you to configure one or more custom output-cache providers. Output-cache providers can use any storage mechanism to persist HTML content. These storage options can include local or remote disks, cloud storage, and distributed cache engines. Output-cache provider extensibility in ASP.NET 4 lets you design more aggressive and more intelligent output-caching strategies for Web sites. For example, you can create an output-cache provider that caches the "Top 10" pages of a site in memory, while caching pages that get lower traffic on disk. Alternatively, you can cache every vary-by combination for a rendered page, but use a distributed cache so that the memory consumption is offloaded from front-end Web servers. You create a custom output-cache provider as a class that derives from the OutputCacheProvider type. You can then configure the provider in the Web.config file by using the new providers subsection of the outputCache element For more information and for examples that show how to configure the output cache, see outputCache Element for caching (ASP.NET Settings Schema). For more information about the classes that support caching, see the documentation for the OutputCache and OutputCacheProvider classes. By default, in ASP.NET 4, all HTTP responses, rendered pages, and controls use the in-memory output cache. The defaultProvider attribute for ASP.NET is AspNetInternalProvider. You can change the default output-cache provider used for a Web application by specifying a different provider name for defaultProvider attribute. In addition, you can select different output-cache providers for individual control and for individual requests and programmatically specify which provider to use. For more information, see the HttpApplication.GetOutputCacheProviderName(HttpContext) method. The easiest way to choose a different output-cache provider for different Web user controls is to do so declaratively by using the new providerName attribute in a page or control directive, as shown in the following example: <%@ OutputCache Duration="60" VaryByParam="None" providerName="DiskCache" %> Preloading Web Applications Some Web applications must load large amounts of data or must perform expensive initialization processing before serving the first request. In earlier versions of ASP.NET, for these situations you had to devise custom approaches to "wake up" an ASP.NET application and then run initialization code during the Application_Load method in the Global.asax file. To address this scenario, a new application preload manager (autostart feature) is available when ASP.NET 4 runs on IIS 7.5 on Windows Server 2008 R2. The preload feature provides a controlled approach for starting up an application pool, initializing an ASP.NET application, and then accepting HTTP requests. It lets you perform expensive application initialization prior to processing the first HTTP request. For example, you can use the application preload manager to initialize an application and then signal a load-balancer that the application was initialized and ready to accept HTTP traffic. To use the application preload manager, an IIS administrator sets an application pool in IIS 7.5 to be automatically started by using the following configuration in the applicationHost.config file: <applicationPools> <add name="MyApplicationPool" startMode="AlwaysRunning" /> </applicationPools> Because a single application pool can contain multiple applications, you specify individual applications to be automatically started by using the following configuration in the applicationHost.config file: <sites> <site name="MySite" id="1"> <application path="/" serviceAutoStartEnabled="true" serviceAutoStartProvider="PrewarmMyCache" > <!-- Additional content --> </application> </site> </sites> <!-- Additional content --> <serviceAutoStartProviders> <add name="PrewarmMyCache" type="MyNamespace.CustomInitialization, MyLibrary" /> </serviceAutoStartProviders> When an IIS 7.5 server is cold-started or when an individual application pool is recycled, IIS 7.5 uses the information in the applicationHost.config file to determine which Web applications have to be automatically started. For each application that is marked for preload, IIS7.5 sends a request to ASP.NET 4 to start the application in a state during which the application temporarily does not accept HTTP requests. When it is in this state, ASP.NET instantiates the type defined by the serviceAutoStartProvider attribute (as shown in the previous example) and calls into its public entry point. You create a managed preload type that has the required entry point by implementing the IProcessHostPreloadClient interface, as shown in the following example: public class CustomInitialization : System.Web.Hosting.IProcessHostPreloadClient { public void Preload(string[] parameters) { // Perform initialization. } } After your initialization code runs in the Preload method and after the method returns, the ASP.NET application is ready to process requests. Permanently Redirecting a Page Content in Web applications is often moved over the lifetime of the application. This can lead to links to be out of date, such as the links that are returned by search engines. In ASP.NET, developers have traditionally handled requests to old URLs by using the Redirect method to forward a request to the new URL. However, the Redirect method issues an HTTP 302 (Found) response (which is used for a temporary redirect). This results in an extra HTTP round trip. ASP.NET 4 adds a RedirectPermanent helper method that makes it easy to issue HTTP 301 (Moved Permanently) responses, as in the following example: RedirectPermanent("/newpath/foroldcontent.aspx"); Search engines and other user agents that recognize permanent redirects will store the new URL that is associated with the content, which eliminates the unnecessary round trip made by the browser for temporary redirects. Session State Compression By default, ASP.NET provides two options for storing session state across a Web farm. The first option is a session state provider that invokes an out-of-process session state server. The second option is a session state provider that stores data in a Microsoft SQL Server database. Because both options store state information outside a Web application's worker process, session state has to be serialized before it is sent to remote storage. If a large amount of data is saved in session state, the size of the serialized data can become very large. ASP.NET 4 introduces a new compression option for both kinds of out-of-process session state providers. By using this option, applications that have spare CPU cycles on Web servers can achieve substantial reductions in the size of serialized session state data. You can set this option using the new compressionEnabled attribute of the sessionState element in the configuration file. When the compressionEnabled configuration option is set to true, ASP.NET compresses (and decompresses) serialized session state by using the .NET Framework GZipStreamclass. The following example shows how to set this attribute. <sessionState mode="SqlServer" sqlConnectionString="data source=dbserver;Initial Catalog=aspnetstate" allowCustomSqlDatabase="true" compressionEnabled="true" /> ASP.NET Web Forms Web Forms has been a core feature in ASP.NET since the release of ASP.NET 1.0. Many enhancements have been in this area for ASP.NET 4, such as the following: The ability to set meta tags. More control over view state. Support for recently introduced browsers and devices. Easier ways to work with browser capabilities. Support for using ASP.NET routing with Web Forms. More control over generated IDs. The ability to persist selected rows in data controls. More control over rendered HTML in the FormView and ListView controls. Filtering support for data source controls. Enhanced support for Web standards and accessibility Setting Meta Tags with the Page.MetaKeywords and Page.MetaDescription Properties Two properties have been added to the Page class: MetaKeywords and MetaDescription. These two properties represent corresponding meta tags in the HTML rendered for a page, as shown in the following example: <head id="Head1" runat="server"> <title>Untitled Page</title> <meta name="keywords" content="keyword1, keyword2' /> <meta name="description" content="Description of my page" /> </head> These two properties work like the Title property does, and they can be set in the @ Page directive. For more information, see Page.MetaKeywords and Page.MetaDescription. Enabling View State for Individual Controls A new property has been added to the Control class: ViewStateMode. You can use this property to disable view state for all controls on a page except those for which you explicitly enable view state. View state data is included in a page's HTML and increases the amount of time it takes to send a page to the client and post it back. Storing more view state than is necessary can cause significant decrease in performance. In earlier versions of ASP.NET, you could reduce the impact of view state on a page's performance by disabling view state for specific controls. But sometimes it is easier to enable view state for a few controls that need it instead of disabling it for many that do not need it. For more information, see Control.ViewStateMode. Support for Recently Introduced Browsers and Devices ASP.NET includes a feature that is named browser capabilities that lets you determine the capabilities of the browser that a user is using. Browser capabilities are represented by the HttpBrowserCapabilities object which is stored in the HttpRequest.Browser property. Information about a particular browser's capabilities is defined by a browser definition file. In ASP.NET 4, these browser definition files have been updated to contain information about recently introduced browsers and devices such as Google Chrome, Research in Motion BlackBerry smart phones, and Apple iPhone. Existing browser definition files have also been updated. For more information, see How to: Upgrade an ASP.NET Web Application to ASP.NET 4 and ASP.NET Web Server Controls and Browser Capabilities. The browser definition files that are included with ASP.NET 4 are shown in the following list: •blackberry.browser •chrome.browser •Default.browser •firefox.browser •gateway.browser •generic.browser •ie.browser •iemobile.browser •iphone.browser •opera.browser •safari.browser A New Way to Define Browser Capabilities ASP.NET 4 includes a new feature referred to as browser capabilities providers. As the name suggests, this lets you build a provider that in turn lets you write custom code to determine browser capabilities. In ASP.NET version 3.5 Service Pack 1, you define browser capabilities in an XML file. This file resides in a machine-level folder or an application-level folder. Most developers do not need to customize these files, but for those who do, the provider approach can be easier than dealing with complex XML syntax. The provider approach makes it possible to simplify the process by implementing a common browser definition syntax, or a database that contains up-to-date browser definitions, or even a Web service for such a database. For more information about the new browser capabilities provider, see the What's New for ASP.NET 4 White Paper. Routing in ASP.NET 4 ASP.NET 4 adds built-in support for routing with Web Forms. Routing is a feature that was introduced with ASP.NET 3.5 SP1 and lets you configure an application to use URLs that are meaningful to users and to search engines because they do not have to specify physical file names. This can make your site more user-friendly and your site content more discoverable by search engines. For example, the URL for a page that displays product categories in your application might look like the following example: http://website/products.aspx?categoryid=12 By using routing, you can use the following URL to render the same information: http://website/products/software The second URL lets the user know what to expect and can result in significantly improved rankings in search engine results. the new features include the following: The PageRouteHandler class is a simple HTTP handler that you use when you define routes. You no longer have to write a custom route handler. The HttpRequest.RequestContext and Page.RouteData properties make it easier to access information that is passed in URL parameters. The RouteUrl expression provides a simple way to create a routed URL in markup. The RouteValue expression provides a simple way to extract URL parameter values in markup. The RouteParameter class makes it easier to pass URL parameter values to a query for a data source control (similar to FormParameter). You no longer have to change the Web.config file to enable routing. For more information about routing, see the following topics: ASP.NET Routing Walkthrough: Using ASP.NET Routing in a Web Forms Application How to: Define Routes for Web Forms Applications How to: Construct URLs from Routes How to: Access URL Parameters in a Routed Page Setting Client IDs The new ClientIDMode property makes it easier to write client script that references HTML elements rendered for server controls. Increasing use of Microsoft Ajax makes the need to do this more common. For example, you may have a data control that renders a long list of products with prices and you want to use client script to make a Web service call and update individual prices in the list as they change without refreshing the entire page. Typically you get a reference to an HTML element in client script by using the document.GetElementById method. You pass to this method the value of the id attribute of the HTML element you want to reference. In the case of elements that are rendered for ASP.NET server controls earlier versions of ASP.NET could make this difficult or impossible. You were not always able to predict what id values ASP.NET would generate, or ASP.NET could generate very long id values. The problem was especially difficult for data controls that would generate multiple rows for a single instance of the control in your markup. ASP.NET 4 adds two new algorithms for generating id attributes. These algorithms can generate id attributes that are easier to work with in client script because they are more predictable and that are easier to work with because they are simpler. For more information about how to use the new algorithms, see the following topics: ASP.NET Web Server Control Identification Walkthrough: Making Data-Bound Controls Easier to Access from JavaScript Walkthrough: Making Controls Located in Web User Controls Easier to Access from JavaScript How to: Access Controls from JavaScript by ID Persisting Row Selection in Data Controls The GridView and ListView controls enable users to select a row. In previous versions of ASP.NET, row selection was based on the row index on the page. For example, if you select the third item on page 1 and then move to page 2, the third item on page 2 is selected. In most cases, is more desirable not to select any rows on page 2. ASP.NET 4 supports Persisted Selection, a new feature that was initially supported only in Dynamic Data projects in the .NET Framework 3.5 SP1. When this feature is enabled, the selected item is based on the row data key. This means that if you select the third row on page 1 and move to page 2, nothing is selected on page 2. When you move back to page 1, the third row is still selected. This is a much more natural behavior than the behavior in earlier versions of ASP.NET. Persisted selection is now supported for the GridView and ListView controls in all projects. You can enable this feature in the GridView control, for example, by setting the EnablePersistedSelection property, as shown in the following example: <asp:GridView id="GridView2" runat="server" PersistedSelection="true"> </asp:GridView> FormView Control Enhancements The FormView control is enhanced to make it easier to style the content of the control with CSS. In previous versions of ASP.NET, the FormView control rendered it contents using an item template. This made styling more difficult in the markup because unexpected table row and table cell tags were rendered by the control. The FormView control supports RenderOuterTable, a property in ASP.NET 4. When this property is set to false, as show in the following example, the table tags are not rendered. This makes it easier to apply CSS style to the contents of the control. <asp:FormView ID="FormView1" runat="server" RenderTable="false"> For more information, see FormView Web Server Control Overview. ListView Control Enhancements The ListView control, which was introduced in ASP.NET 3.5, has all the functionality of the GridView control while giving you complete control over the output. This control has been made easier to use in ASP.NET 4. The earlier version of the control required that you specify a layout template that contained a server control with a known ID. The following markup shows a typical example of how to use the ListView control in ASP.NET 3.5. <asp:ListView ID="ListView1" runat="server"> <LayoutTemplate> <asp:PlaceHolder ID="ItemPlaceHolder" runat="server"></asp:PlaceHolder> </LayoutTemplate> <ItemTemplate> <% Eval("LastName")%> </ItemTemplate> </asp:ListView> In ASP.NET 4, the ListView control does not require a layout template. The markup shown in the previous example can be replaced with the following markup: <asp:ListView ID="ListView1" runat="server"> <ItemTemplate> <% Eval("LastName")%> </ItemTemplate> </asp:ListView> For more information, see ListView Web Server Control Overview. Filtering Data with the QueryExtender Control A very common task for developers who create data-driven Web pages is to filter data. This traditionally has been performed by building Where clauses in data source controls. This approach can be complicated, and in some cases the Where syntax does not let you take advantage of the full functionality of the underlying database. To make filtering easier, a new QueryExtender control has been added in ASP.NET 4. This control can be added to EntityDataSource or LinqDataSource controls in order to filter the data returned by these controls. Because the QueryExtender control relies on LINQ, but you do not to need to know how to write LINQ queries to use the query extender. The QueryExtender control supports a variety of filter options. The following lists QueryExtender filter options. Term Definition SearchExpression Searches a field or fields for string values and compares them to a specified string value. RangeExpression Searches a field or fields for values in a range specified by a pair of values. PropertyExpression Compares a specified value to a property value in a field. If the expression evaluates to true, the data that is being examined is returned. OrderByExpression Sorts data by a specified column and sort direction. CustomExpression Calls a function that defines custom filter in the page. For more information, see QueryExtenderQueryExtender Web Server Control Overview. Enhanced Support for Web Standards and Accessibility Earlier versions of ASP.NET controls sometimes render markup that does not conform to HTML, XHTML, or accessibility standards. ASP.NET 4 eliminates most of these exceptions. For details about how the HTML that is rendered by each control meets accessibility standards, see ASP.NET Controls and Accessibility. CSS for Controls that Can be Disabled In ASP.NET 3.5, when a control is disabled (see WebControl.Enabled), a disabled attribute is added to the rendered HTML element. For example, the following markup creates a Label control that is disabled: <asp:Label id="Label1" runat="server"   Text="Test" Enabled="false" /> In ASP.NET 3.5, the previous control settings generate the following HTML: <span id="Label1" disabled="disabled">Test</span> In HTML 4.01, the disabled attribute is not considered valid on span elements. It is valid only on input elements because it specifies that they cannot be accessed. On display-only elements such as span elements, browsers typically support rendering for a disabled appearance, but a Web page that relies on this non-standard behavior is not robust according to accessibility standards. For display-only elements, you should use CSS to indicate a disabled visual appearance. Therefore, by default ASP.NET 4 generates the following HTML for the control settings shown previously: <span id="Label1" class="aspNetDisabled">Test</span> You can change the value of the class attribute that is rendered by default when a control is disabled by setting the DisabledCssClass property. CSS for Validation Controls In ASP.NET 3.5, validation controls render a default color of red as an inline style. For example, the following markup creates a RequiredFieldValidator control: <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server"   ErrorMessage="Required Field" ControlToValidate="RadioButtonList1" /> ASP.NET 3.5 renders the following HTML for the validator control: <span id="RequiredFieldValidator1"   style="color:Red;visibility:hidden;">RequiredFieldValidator</span> By default, ASP.NET 4 does not render an inline style to set the color to red. An inline style is used only to hide or show the validator, as shown in the following example: <span id="RequiredFieldValidator1"   style"visibility:hidden;">RequiredFieldValidator</span> Therefore, ASP.NET 4 does not automatically show error messages in red. For information about how to use CSS to specify a visual style for a validation control, see Validating User Input in ASP.NET Web Pages. CSS for the Hidden Fields Div Element ASP.NET uses hidden fields to store state information such as view state and control state. These hidden fields are contained by a div element. In ASP.NET 3.5, this div element does not have a class attribute or an id attribute. Therefore, CSS rules that affect all div elements could unintentionally cause this div to be visible. To avoid this problem, ASP.NET 4 renders the div element for hidden fields with a CSS class that you can use to differentiate the hidden fields div from others. The new classvalue is shown in the following example: <div class="aspNetHidden"> CSS for the Table, Image, and ImageButton Controls By default, in ASP.NET 3.5, some controls set the border attribute of rendered HTML to zero (0). The following example shows HTML that is generated by the Table control in ASP.NET 3.5: <table id="Table2" border="0"> The Image control and the ImageButton control also do this. Because this is not necessary and provides visual formatting information that should be provided by using CSS, the attribute is not generated in ASP.NET 4. CSS for the UpdatePanel and UpdateProgress Controls In ASP.NET 3.5, the UpdatePanel and UpdateProgress controls do not support expando attributes. This makes it impossible to set a CSS class on the HTMLelements that they render. In ASP.NET 4 these controls have been changed to accept expando attributes, as shown in the following example: <asp:UpdatePanel runat="server" class="myStyle"> </asp:UpdatePanel> The following HTML is rendered for this markup: <div id="ctl00_MainContent_UpdatePanel1" class="expandoclass"> </div> Eliminating Unnecessary Outer Tables In ASP.NET 3.5, the HTML that is rendered for the following controls is wrapped in a table element whose purpose is to apply inline styles to the entire control: FormView Login PasswordRecovery ChangePassword If you use templates to customize the appearance of these controls, you can specify CSS styles in the markup that you provide in the templates. In that case, no extra outer table is required. In ASP.NET 4, you can prevent the table from being rendered by setting the new RenderOuterTable property to false. Layout Templates for Wizard Controls In ASP.NET 3.5, the Wizard and CreateUserWizard controls generate an HTML table element that is used for visual formatting. In ASP.NET 4 you can use a LayoutTemplate element to specify the layout. If you do this, the HTML table element is not generated. In the template, you create placeholder controls to indicate where items should be dynamically inserted into the control. (This is similar to how the template model for the ListView control works.) For more information, see the Wizard.LayoutTemplate property. New HTML Formatting Options for the CheckBoxList and RadioButtonList Controls ASP.NET 3.5 uses HTML table elements to format the output for the CheckBoxList and RadioButtonList controls. To provide an alternative that does not use tables for visual formatting, ASP.NET 4 adds two new options to the RepeatLayout enumeration: UnorderedList. This option causes the HTML output to be formatted by using ul and li elements instead of a table. OrderedList. This option causes the HTML output to be formatted by using ol and li elements instead of a table. For examples of HTML that is rendered for the new options, see the RepeatLayout enumeration. Header and Footer Elements for the Table Control In ASP.NET 3.5, the Table control can be configured to render thead and tfoot elements by setting the TableSection property of the TableHeaderRow class and the TableFooterRow class. In ASP.NET 4 these properties are set to the appropriate values by default. CSS and ARIA Support for the Menu Control In ASP.NET 3.5, the Menu control uses HTML table elements for visual formatting, and in some configurations it is not keyboard-accessible. ASP.NET 4 addresses these problems and improves accessibility in the following ways: The generated HTML is structured as an unordered list (ul and li elements). CSS is used for visual formatting. The menu behaves in accordance with ARIA standards for keyboard access. You can use arrow keys to navigate menu items. (For information about ARIA, see Accessibility in Visual Studio and ASP.NET.) ARIA role and property attributes are added to the generated HTML. (Attributes are added by using JavaScript instead of included in the HTML, to avoid generating HTML that would cause markup validation errors.) Styles for the Menu control are rendered in a style block at the top of the page, instead of inline with the rendered HTML elements. If you want to use a separate CSS file so that you can modify the menu styles, you can set the Menu control's new IncludeStyleBlock property to false, in which case the style block is not generated. Valid XHTML for the HtmlForm Control In ASP.NET 3.5, the HtmlForm control (which is created implicitly by the <form runat="server"> tag) renders an HTML form element that has both name and id attributes. The name attribute is deprecated in XHTML 1.1. Therefore, this control does not render the name attribute in ASP.NET 4. Maintaining Backward Compatibility in Control Rendering An existing ASP.NET Web site might have code in it that assumes that controls are rendering HTML the way they do in ASP.NET 3.5. To avoid causing backward compatibility problems when you upgrade the site to ASP.NET 4, you can have ASP.NET continue to generate HTML the way it does in ASP.NET 3.5 after you upgrade the site. To do so, you can set the controlRenderingCompatibilityVersion attribute of the pages element to "3.5" in the Web.config file of an ASP.NET 4 Web site, as shown in the following example: <system.web>   <pages controlRenderingCompatibilityVersion="3.5"/> </system.web> If this setting is omitted, the default value is the same as the version of ASP.NET that the Web site targets. (For information about multi-targeting in ASP.NET, see .NET Framework Multi-Targeting for ASP.NET Web Projects.) ASP.NET MVC ASP.NET MVC helps Web developers build compelling standards-based Web sites that are easy to maintain because it decreases the dependency among application layers by using the Model-View-Controller (MVC) pattern. MVC provides complete control over the page markup. It also improves testability by inherently supporting Test Driven Development (TDD). Web sites created using ASP.NET MVC have a modular architecture. This allows members of a team to work independently on the various modules and can be used to improve collaboration. For example, developers can work on the model and controller layers (data and logic), while the designer work on the view (presentation). For tutorials, walkthroughs, conceptual content, code samples, and a complete API reference, see ASP.NET MVC 2. Dynamic Data Dynamic Data was introduced in the .NET Framework 3.5 SP1 release in mid-2008. This feature provides many enhancements for creating data-driven applications, such as the following: A RAD experience for quickly building a data-driven Web site. Automatic validation that is based on constraints defined in the data model. The ability to easily change the markup that is generated for fields in the GridView and DetailsView controls by using field templates that are part of your Dynamic Data project. For ASP.NET 4, Dynamic Data has been enhanced to give developers even more power for quickly building data-driven Web sites. For more information, see ASP.NET Dynamic Data Content Map. Enabling Dynamic Data for Individual Data-Bound Controls in Existing Web Applications You can use Dynamic Data features in existing ASP.NET Web applications that do not use scaffolding by enabling Dynamic Data for individual data-bound controls. Dynamic Data provides the presentation and data layer support for rendering these controls. When you enable Dynamic Data for data-bound controls, you get the following benefits: Setting default values for data fields. Dynamic Data enables you to provide default values at run time for fields in a data control. Interacting with the database without creating and registering a data model. Automatically validating the data that is entered by the user without writing any code. For more information, see Walkthrough: Enabling Dynamic Data in ASP.NET Data-Bound Controls. New Field Templates for URLs and E-mail Addresses ASP.NET 4 introduces two new built-in field templates, EmailAddress.ascx and Url.ascx. These templates are used for fields that are marked as EmailAddress or Url using the DataTypeAttribute attribute. For EmailAddress objects, the field is displayed as a hyperlink that is created by using the mailto: protocol. When users click the link, it opens the user's e-mail client and creates a skeleton message. Objects typed as Url are displayed as ordinary hyperlinks. The following example shows how to mark fields. [DataType(DataType.EmailAddress)] public object HomeEmail { get; set; } [DataType(DataType.Url)] public object Website { get; set; } Creating Links with the DynamicHyperLink Control Dynamic Data uses the new routing feature that was added in the .NET Framework 3.5 SP1 to control the URLs that users see when they access the Web site. The new DynamicHyperLink control makes it easy to build links to pages in a Dynamic Data site. For information, see How to: Create Table Action Links in Dynamic Data Support for Inheritance in the Data Model Both the ADO.NET Entity Framework and LINQ to SQL support inheritance in their data models. An example of this might be a database that has an InsurancePolicy table. It might also contain CarPolicy and HousePolicy tables that have the same fields as InsurancePolicy and then add more fields. Dynamic Data has been modified to understand inherited objects in the data model and to support scaffolding for the inherited tables. For more information, see Walkthrough: Mapping Table-per-Hierarchy Inheritance in Dynamic Data. Support for Many-to-Many Relationships (Entity Framework Only) The Entity Framework has rich support for many-to-many relationships between tables, which is implemented by exposing the relationship as a collection on an Entity object. New field templates (ManyToMany.ascx and ManyToMany_Edit.ascx) have been added to provide support for displaying and editing data that is involved in many-to-many relationships. For more information, see Working with Many-to-Many Data Relationships in Dynamic Data. New Attributes to Control Display and Support Enumerations The DisplayAttribute has been added to give you additional control over how fields are displayed. The DisplayNameAttribute attribute in earlier versions of Dynamic Data enabled you to change the name that is used as a caption for a field. The new DisplayAttribute class lets you specify more options for displaying a field, such as the order in which a field is displayed and whether a field will be used as a filter. The attribute also provides independent control of the name that is used for the labels in a GridView control, the name that is used in a DetailsView control, the help text for the field, and the watermark used for the field (if the field accepts text input). The EnumDataTypeAttribute class has been added to let you map fields to enumerations. When you apply this attribute to a field, you specify an enumeration type. Dynamic Data uses the new Enumeration.ascx field template to create UI for displaying and editing enumeration values. The template maps the values from the database to the names in the enumeration. Enhanced Support for Filters Dynamic Data 1.0 had built-in filters for Boolean columns and foreign-key columns. The filters did not let you specify the order in which they were displayed. The new DisplayAttribute attribute addresses this by giving you control over whether a column appears as a filter and in what order it will be displayed. An additional enhancement is that filtering support has been rewritten to use the new QueryExtender feature of Web Forms. This lets you create filters without requiring knowledge of the data source control that the filters will be used with. Along with these extensions, filters have also been turned into template controls, which lets you add new ones. Finally, the DisplayAttribute class mentioned earlier allows the default filter to be overridden, in the same way that UIHint allows the default field template for a column to be overridden. For more information, see Walkthrough: Filtering Rows in Tables That Have a Parent-Child Relationship and QueryableFilterRepeater. ASP.NET Chart Control The ASP.NET chart server control enables you to create ASP.NET pages applications that have simple, intuitive charts for complex statistical or financial analysis. The chart control supports the following features: Data series, chart areas, axes, legends, labels, titles, and more. Data binding. Data manipulation, such as copying, splitting, merging, alignment, grouping, sorting, searching, and filtering. Statistical formulas and financial formulas. Advanced chart appearance, such as 3-D, anti-aliasing, lighting, and perspective. Events and customizations. Interactivity and Microsoft Ajax. Support for the Ajax Content Delivery Network (CDN), which provides an optimized way for you to add Microsoft Ajax Library and jQuery scripts to your Web applications. For more information, see Chart Web Server Control Overview. Visual Web Developer Enhancements The following sections provide information about enhancements and new features in Visual Studio 2010 and Visual Web Developer Express. The Web page designer in Visual Studio 2010 has been enhanced for better CSS compatibility, includes additional support for HTML and ASP.NET markup snippets, and features a redesigned version of IntelliSense for JScript. Improved CSS Compatibility The Visual Web Developer designer in Visual Studio 2010 has been updated to improve CSS 2.1 standards compliance. The designer better preserves HTML source code and is more robust than in previous versions of Visual Studio. HTML and JScript Snippets In the HTML editor, IntelliSense auto-completes tag names. The IntelliSense Snippets feature auto-completes whole tags and more. In Visual Studio 2010, IntelliSense snippets are supported for JScript, alongside C# and Visual Basic, which were supported in earlier versions of Visual Studio. Visual Studio 2010 includes over 200 snippets that help you auto-complete common ASP.NET and HTML tags, including required attributes (such as runat="server") and common attributes specific to a tag (such as ID, DataSourceID, ControlToValidate, and Text). You can download additional snippets, or you can write your own snippets that encapsulate the blocks of markup that you or your team use for common tasks. For more information on HTML snippets, see Walkthrough: Using HTML Snippets. JScript IntelliSense Enhancements In Visual 2010, JScript IntelliSense has been redesigned to provide an even richer editing experience. IntelliSense now recognizes objects that have been dynamically generated by methods such as registerNamespace and by similar techniques used by other JavaScript frameworks. Performance has been improved to analyze large libraries of script and to display IntelliSense with little or no processing delay. Compatibility has been significantly increased to support almost all third-party libraries and to support diverse coding styles. Documentation comments are now parsed as you type and are immediately leveraged by IntelliSense. Web Application Deployment with Visual Studio 2010 For Web application projects, Visual Studio now provides tools that work with the IIS Web Deployment Tool (Web Deploy) to automate many processes that had to be done manually in earlier versions of ASP.NET. For example, the following tasks can now be automated: Creating an IIS application on the destination computer and configuring IIS settings. Copying files to the destination computer. Changing Web.config settings that must be different in the destination environment. Propagating changes to data or data structures in SQL Server databases that are used by the Web application. For more information about Web application deployment, see ASP.NET Deployment Content Map. Enhancements to ASP.NET Multi-Targeting ASP.NET 4 adds new features to the multi-targeting feature to make it easier to work with projects that target earlier versions of the .NET Framework. Multi-targeting was introduced in ASP.NET 3.5 to enable you to use the latest version of Visual Studio without having to upgrade existing Web sites or Web services to the latest version of the .NET Framework. In Visual Studio 2008, when you work with a project targeted for an earlier version of the .NET Framework, most features of the development environment adapt to the targeted version. However, IntelliSense displays language features that are available in the current version, and property windows display properties available in the current version. In Visual Studio 2010, only language features and properties available in the targeted version of the .NET Framework are shown. For more information about multi-targeting, see the following topics: .NET Framework Multi-Targeting for ASP.NET Web Projects ASP.NET Side-by-Side Execution Overview How to: Host Web Applications That Use Different Versions of the .NET Framework on the Same Server How to: Deploy Web Site Projects Targeted for Earlier Versions of the .NET Framework

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• June 26th Links: ASP.NET, ASP.NET MVC, .NET and NuGet

  - by ScottGu

  Here is the latest in my link-listing series.  Also check out my Best of 2010 Summary for links to 100+ other posts I’ve done in the last year. [I am also now using Twitter for quick updates and to share links. Follow me at: twitter.com/scottgu] ASP.NET Introducing new ASP.NET Universal Providers: Great post from Scott Hanselman on the new System.Web.Providers we are working on.  This release delivers new ASP.NET Membership, Role Management, Session, Profile providers that work with SQL Server, SQL CE and SQL Azure. CSS Sprites and the ASP.NET Sprite and Image Optimization Library: Great post from Scott Mitchell that talks about a free library for ASP.NET that you can use to optimize your CSS and images to reduce HTTP requests and speed up your site. Better HTML5 Support for the VS 2010 Editor: Another great post from Scott Hanselman on an update several people on my team did that enables richer HTML5 editing support within Visual Studio 2010. Install the Ajax Control Toolkit from NuGet: Nice post by Stephen Walther on how you can now use NuGet to install the Ajax Control Toolkit within your applications.  This makes it much easier to reference and use. May 2011 Release of the Ajax Control Toolkit: Another great post from Stephen Walther that talks about the May release of the Ajax Control Toolkit. It includes a bunch of nice enhancements and fixes. SassAndCoffee 0.9 Released: Paul Betts blogs about the latest release of his SassAndCoffee extension (available via NuGet). It enables you to easily use Sass and Coffeescript within your ASP.NET applications (both MVC and Webforms). ASP.NET MVC ASP.NET MVC Mini-Profiler: The folks at StackOverflow.com (a great site built with ASP.NET MVC) have released a nice (free) profiler they’ve built that enables you to easily profile your ASP.NET MVC 3 sites and tune them for performance.  Globalization, Internationalization and Localization in ASP.NET MVC 3: Great post from Scott Hanselman on how to enable internationalization, globalization and localization support within your ASP.NET MVC 3 and jQuery solutions. Precompile your MVC Razor Views: Great post from David Ebbo that discusses a new Razor Generator tool that enables you to pre-compile your razor view templates as assemblies – which enables a bunch of cool scenarios. Unit Testing Razor Views: Nice post from David Ebbo that shows how to use his new Razor Generator to enable unit testing of razor view templates with ASP.NET MVC. Bin Deploying ASP.NET MVC 3: Nice post by Phil Haack that covers a cool feature added to VS 2010 SP1 that makes it really easy to \bin deploy ASP.NET MVC and Razor within your application. This enables you to easily deploy the app to servers that don’t have ASP.NET MVC 3 installed. .NET Table Splitting with EF 4.1 Code First: Great post from Morteza Manavi that discusses how to split up a single database table across multiple EF entity classes.  This shows off some of the power behind EF 4.1 and is very useful when working with legacy database schemas. Choosing the Right Collection Class: Nice post from James Michael Hare that talks about the different collection class options available within .NET.  A nice overview for people who haven’t looked at all of the support now built into the framework. Little Wonders: Empty(), DefaultIfEmpty() and Count() helper methods: Another in James Michael Hare’s excellent series on .NET/C# “Little Wonders”.  This post covers some of the great helper methods now built-into .NET that make coding even easier. NuGet NuGet 1.4 Released: Learn all about the latest release of NuGet – which includes a bunch of cool new capabilities.  It takes only seconds to update to it – go for it! NuGet in Depth: Nice presentation from Scott Hanselman all about NuGet and some of the investments we are making to enable a better open source ecosystem within .NET. NuGet for the Enterprise – NuGet in a Continuous Integration Automated Build System: Great post from Scott Hanselman on how to integrate NuGet within enterprise build environments and enable it with CI solutions. Hope this helps, Scott

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• Custom ASP.Net MVC 2 ModelMetadataProvider for using custom view model attributes

  - by SeanMcAlinden

  There are a number of ways of implementing a pattern for using custom view model attributes, the following is similar to something I’m using at work which works pretty well. The classes I’m going to create are really simple: 1. Abstract base attribute 2. Custom ModelMetadata provider which will derive from the DataAnnotationsModelMetadataProvider   Base Attribute MetadataAttribute using System; using System.Web.Mvc; namespace Mvc2Templates.Attributes {     /// <summary>     /// Base class for custom MetadataAttributes.     /// </summary>     public abstract class MetadataAttribute : Attribute     {         /// <summary>         /// Method for processing custom attribute data.         /// </summary>         /// <param name="modelMetaData">A ModelMetaData instance.</param>         public abstract void Process(ModelMetadata modelMetaData);     } } As you can see, the class simple has one method – Process. Process accepts the ModelMetaData which will allow any derived custom attributes to set properties on the model meta data and add items to its AdditionalValues collection.   Custom Model Metadata Provider For a quick explanation of the Model Metadata and how it fits in to the MVC 2 framework, it is basically a set of properties that are usually set via attributes placed above properties on a view model, for example the ReadOnly and HiddenInput attributes. When EditorForModel, DisplayForModel or any of the other EditorFor/DisplayFor methods are called, the ModelMetadata information is used to determine how to display the properties. All of the information available within the model metadata is also available through ViewData.ModelMetadata. The following class derives from the DataAnnotationsModelMetadataProvider built into the mvc 2 framework. I’ve overridden the CreateMetadata method in order to process any custom attributes that may have been placed above a property in a view model.   CustomModelMetadataProvider using System; using System.Collections.Generic; using System.Linq; using System.Web.Mvc; using Mvc2Templates.Attributes; namespace Mvc2Templates.Providers {     public class CustomModelMetadataProvider : DataAnnotationsModelMetadataProvider     {         protected override ModelMetadata CreateMetadata(             IEnumerable<Attribute> attributes,             Type containerType,             Func<object> modelAccessor,             Type modelType,             string propertyName)         {             var modelMetadata = base.CreateMetadata(attributes, containerType, modelAccessor, modelType, propertyName);               attributes.OfType<MetadataAttribute>().ToList().ForEach(x => x.Process(modelMetadata));               return modelMetadata;         }     } } As you can see, once the model metadata is created through the base method, a check for any attributes deriving from our new abstract base attribute MetadataAttribute is made, the Process method is then called on any existing custom attributes with the model meta data for the property passed in.   Hooking it up The last thing you need to do to hook it up is set the new CustomModelMetadataProvider as the current ModelMetadataProvider, this is done within the Global.asax Application_Start method. Global.asax protected void Application_Start()         {             AreaRegistration.RegisterAllAreas();               RegisterRoutes(RouteTable.Routes);               ModelMetadataProviders.Current = new CustomModelMetadataProvider();         }   In my next post, I’m going to demonstrate a cool custom attribute that turns a textbox into an ajax driven AutoComplete text box. Hope this is useful. Kind Regards, Sean McAlinden.

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• Microsoft silverlight 5.0 features for developers

  - by Jalpesh P. Vadgama

  Recently on Silverlight 5.0 firestarter event ScottGu has announced road map for Silverlight 5.0. There will be lots of features that will be there in silverlight 5.0 but here are few glimpses of Silverlight 5.0 Features. Improved Data binding support and Better support for MVVM: One of the greatest strength of Silverlight is its data binding. Microsoft is going to enhanced data binding by providing more ability to debug it. Developer will able to debug the binding expression and other stuff in Siverlight 5.0. Its also going to provide Ancestor Relative source binding which will allow property to bind with container control. MVVM pattern support will also be enhanced. Performance and Speed Enhancement: Now silverlight 5.0 will have support for 64bit browser support. So now you can use that silverlight application on 64 bit platform also. There is no need to take extra care for it.It will also have faster startup time and greater support for hardware acceleration. It will also provide end to end support for hard acceleration features of IE 9. More support for Out Of Browser Application: With Siverlight 4.0 Microsoft has announced new features called out of browser application and it has amazed lots of developer because now possibilities are unlimited with it. Now in silverlight 5.0 Out Of Browser application will have ability to Create Manage child windows just like windows forms or WPF Application. So you can fill power of desktop application with your out of browser application. Testing Support with Visual Studio 2010: Microsoft is going to add automated UI Testing support with Visual Studio 2010 with silverlight 5.0. So now we can test UI of Silverlight much faster. Better Support for RIA Services: RIA Services allows us to create N-tier application with silverlight via creating proxy classes on client and server both side. Now it will more features like complex type support, Custom type support for MVVM(Model View View Model) pattern. WCF Enhancements: There are lots of enhancement with WCF but key enhancement will WSTrust support. Text and Printing Support: Silverlight 5.0 will support vector base graphics. It will also support multicolumn text flow and linked text containers. It will full open type support,Postscript vector enhancement. Improved Power Enhancement: This will prevent screensaver from activating while you are watching videos on silverlight. Silverlight 5.0 is going add that smartness so it can determine while you are going to watch video and while you are not going watch videos. Better support for graphics: Silverlight 5.0 will provide in-depth support for 3D API. Now 3D rendering support is more enhancement in silverlight and 3D graphics can be rendered easily. You can find more details on following links and also don’t forgot to view silverlight firestarter keynot video of scottgu. http://www.silverlight.net/news/events/firestarter-labs/ http://blogs.msdn.com/b/katriend/archive/2010/12/06/silverlight-5-features-firestarter-keynote-and-sessions-resources.aspx http://weblogs.asp.net/scottgu/archive/2010/12/02/announcing-silverlight-5.aspx http://www.silverlight.net/news/events/firestarter/ http://www.microsoft.com/silverlight/future/ Hope this will help you. Stay tuned!!!.

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• Implementing Release Notes in TFS Team Build 2010

  - by Jakob Ehn

  In TFS Team Build (all versions), each build is associated with changesets and work items. To determine which changesets that should be associated with the current build, Team Build finds the label of the “Last Good Build” an then aggregates all changesets up unitl the label for the current build. Basically this means that if your build is failing, every changeset that is checked in will be accumulated in this list until the build is successful. All well, but there uis a dimension missing here, regarding to releases. Often you can run several release builds until you actually deploy the result of the build to a test or production system. When you do this, wouldn’t it be nice to be able to send the customer a nice release note that contain all work items and changeset since the previously deployed version? At our company, we have developed a Release Repository, which basically is a siple web site with a SQL database as storage. Every time we run a Release Build, the resulting installers, zip-files, sql scripts etc, gets pushed into the release repositor together with the relevant build information. This information contains things such as start time, who triggered the build etc. Also, it contains the associated changesets and work items. When deploying the MSI’s for a new version, we mark the build as Deployed in the release repository. The depoyed status is stored in the release repository database, but it could also have been implemented by setting the Build Quality for that build to Deployed. When generating the release notes, the web site simple runs through each release build back to the previous build that was marked as Deplyed, and aggregates the work items and changesets: Here is a sample screenshot on how this looks for a sample build/application The web site is available both for us and also for the customers and testers, which means that they can easily get the latest version of a particular application and at the same time see what changes are included in this version. There is a lot going on in the Release Build Process that drives this in our TFS 2010 server, but in this post I will show how you can access and read the changeset and work item information in a custom activity. Since Team Build associates changesets and work items for each build, this information is (partially) available inside the build process template. The Associate Changesets and Work Items for non-Shelveset Builds activity (located inside the Try  Compile, Test, and Associate Changesets and Work Items activity) defines and populates a variable called associatedWorkItems   You can see that this variable is an IList containing instances of the Changeset class (from the Microsoft.TeamFoundation.VersionControl.Client namespace). Now, if you want to access this variable later on in the build process template, you need to declare a new variable in the corresponding scope and the assign the value to this variable. In this sample, I declared a variable called assocChangesets in the RunAgent sequence, which basically covers the whol compile, test and drop part of the build process:   Now, you need to assign the value from the AssociatedChangesets to this variable. This is done using the Assign workflow activity:   Now you can add a custom activity any where inside the RunAgent sequence and use this variable. NB: Of course your activity must place somewhere after the variable has been poplated. To finish off, here is code snippet that shows how you can read the changeset and work item information from the variable.   First you add an InArgumet on your activity where you can pass i the variable that we defined. [RequiredArgument] public InArgument<IList<Changeset>> AssociatedChangesets { get; set; } Then you can traverse all the changesets in the list, and for each changeset use the WorkItems property to get the work items that were associated in that changeset: foreach (Changeset ch in associatedChangesets) { // Add change theChangesets.Add( new AssociatedChangeset(ch.ChangesetId, ch.ArtifactUri, ch.Committer, ch.Comment, ch.ChangesetId)); foreach (var wi in ch.WorkItems) { theWorkItems.Add( new AssociatedWorkItem(wi["System.AssignedTo"].ToString(), wi.Id, wi["System.State"].ToString(), wi.Title, wi.Type.Name, wi.Id, wi.Uri)); } } NB: AssociatedChangeset and AssociatedWorkItem are custom classes that we use internally for storing this information that is eventually pushed to the release repository.

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• GPGPU

  WhatGPU obviously stands for Graphics Processing Unit (the silicon powering the display you are using to read this blog post). The extra GP in front of that stands for General Purpose computing.So, altogether GPGPU refers to computing we can perform on GPU for purposes beyond just drawing on the screen. In effect, we can use a GPGPU a bit like we already use a CPU: to perform some calculation (that doesn’t have to have any visual element to it). The attraction is that a GPGPU can be orders of magnitude faster than a CPU.WhyWhen I was at the SuperComputing conference in Portland last November, GPGPUs were all the rage. A quick online search reveals many articles introducing the GPGPU topic. I'll just share 3 here: pcper (ignoring all pages except the first, it is a good consumer perspective), gizmodo (nice take using mostly layman terms) and vizworld (answering the question on "what's the big deal").The GPGPU programming paradigm (from a high level) is simple: in your CPU program you define functions (aka kernels) that take some input, can perform the costly operation and return the output. The kernels are the things that execute on the GPGPU leveraging its power (and hence execute faster than what they could on the CPU) while the host CPU program waits for the results or asynchronously performs other tasks.However, GPGPUs have different characteristics to CPUs which means they are suitable only for certain classes of problem (i.e. data parallel algorithms) and not for others (e.g. algorithms with branching or recursion or other complex flow control). You also pay a high cost for transferring the input data from the CPU to the GPU (and vice versa the results back to the CPU), so the computation itself has to be long enough to justify the overhead transfer costs. If your problem space fits the criteria then you probably want to check out this technology.HowSo where can you get a graphics card to start playing with all this? At the time of writing, the two main vendors ATI (owned by AMD) and NVIDIA are the obvious players in this industry. You can read about GPGPU on this AMD page and also on this NVIDIA page. NVIDIA's website also has a free chapter on the topic from the "GPU Gems" book: A Toolkit for Computation on GPUs.If you followed the links above, then you've already come across some of the choices of programming models that are available today. Essentially, AMD is offering their ATI Stream technology accessible via a language they call Brook+; NVIDIA offers their CUDA platform which is accessible from CUDA C. Choosing either of those locks you into the GPU vendor and hence your code cannot run on systems with cards from the other vendor (e.g. imagine if your CPU code would run on Intel chips but not AMD chips). Having said that, both vendors plan to support a new emerging standard called OpenCL, which theoretically means your kernels can execute on any GPU that supports it. To learn more about all of these there is a website: gpgpu.org. The caveat about that site is that (currently) it completely ignores the Microsoft approach, which I touch on next.On Windows, there is already a cross-GPU-vendor way of programming GPUs and that is the DirectX API. Specifically, on Windows Vista and Windows 7, the DirectX 11 API offers a dedicated subset of the API for GPGPU programming: DirectCompute. You use this API on the CPU side, to set up and execute the kernels that run on the GPU. The kernels are written in a language called HLSL (High Level Shader Language). You can use DirectCompute with HLSL to write a "compute shader", which is the term DirectX uses for what I've been referring to in this post as a "kernel". For a comprehensive collection of links about this (including tutorials, videos and samples) please see my blog post: DirectCompute.Note that there are many efforts to build even higher level languages on top of DirectX that aim to expose GPGPU programming to a wider audience by making it as easy as today's mainstream programming models. I'll mention here just two of those efforts: Accelerator from MSR and Brahma by Ananth. Comments about this post welcome at the original blog.

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• How to configure Visual Studio 2010 code coverage for ASP.NET MVC unit tests

  - by DigiMortal

  I just got Visual Studio 2010 code coverage work with ASP.NET MVC application unit tests. Everything is simple after you have spent some time with forums, blogs and Google. To save your valuable time I wrote this posting to guide you through the process of making code coverage work with ASP.NET MVC application unit tests. After some fighting with Visual Studio I got everything to work as expected. I am still not very sure why users must deal with this mess, but okay – I survived it. Before you start configuring Visual Studio I expect your solution meets the following needs: there are at least one library that will be tested, there is at least on library that contains tests to be run, there are some classes and some tests for them, and, of course, you are using version of Visual Studio 2010 that supports tests (I have Visual Studio 2010 Ultimate). Now open the following screenshot to separate windows and follow the steps given below. Visual Studio 2010 Test Settings window. Click on image to see it at original size.  Double click on Local.testsettings under Solution Items. Test settings window will be opened. Select “Data and Diagnostics” from left pane. Mark checkboxes “ASP.NET Profiler” and “Code Coverage”. Move cursor to “Code Coverage” line and press Configure button or make double click on line. Assemblies selection window will be opened. Mark checkboxes that are located before assemblies about what you want code coverage reports and apply settings. Save your project and close Visual Studio. Run Visual Studio as Administrator and run tests. NB! Select Test => Run => Tests in Current Context from menu. When tests are run you can open code coverage results by selecting Test => Windows => Code Coverage Results from menu. Here you can see my example test results. Visual Studio 2010 Test Results window. All my tests passed this time. :) Click on image to see it at original size.  And here are the code coverage results. Visual Studio 2101 Code Coverage Results. I need a lot more tests for sure. Click on image to see it at original size.  As you can see everything was pretty simple. But it took me sometime to figure out how to get everything work as expected. Problems? You may face some problems when making code coverage work. Here is my short list of possible problems. Make sure you have all assemblies available for code coverage. In some cases it needs more libraries to be referenced as you currently have. By example, I had to add some more Enterprise Library assemblies to my project. You can use EventViewer to discover errors that where given during testing. Make sure you selected all testable assemblies from Code Coverage settings like shown above. Otherwise you may get empty results. Tests with code coverage are slower because we need ASP.NET profiler. If your machine slows down then try to free more resources.

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• Windows Presentation Foundation 4.5 Cookbook Review

  - by Ricardo Peres

  As promised, here’s my review of Windows Presentation Foundation 4.5 Cookbook, that Packt Publishing kindly made available to me. It is an introductory book, targeted at WPF newcomers or users with few experience, following the typical recipes or cookbook style. Like all Packt Publishing books on development, each recipe comes with sample code that is self-sufficient for understanding the concepts it tries to illustrate. It starts on chapter 1 by introducing the most important concepts, the XAML language itself, what can be declared in XAML and how to do it, what are dependency and attached properties as well as markup extensions and events, which should give readers a most required introduction to how WPF works and how to do basic stuff. It moves on to resources on chapter 2, which also makes since, since it’s such an important concept in WPF. Next, chapter 3, come the panels used for laying controls on the screen, all of the out of the box panels are described with typical use cases. Controls come next in chapter 4; the difference between elements and controls is introduced, as well as content controls, headered controls and items controls, and all standard controls are introduced. The book shows how to change the way they look by using templates. The next chapter, 5, talks about top level windows and the WPF application object: how to access startup arguments, how to set the main window, using standard dialogs and there’s even a sample on how to have a irregularly-shaped window. This is one of the most important concepts in WPF: data binding, which is the theme for the following chapter, 6. All common scenarios are introduced, the binding modes, directions, triggers, etc. It talks about the INotifyPropertyChanged interface and how to use it for notifying data binding subscribers of changes in data sources. Data templates and selectors are also covered, as are value converters and data triggers. Examples include master-detail and sorting, grouping and filtering collections and binding trees and grids. Last it covers validation rules and error templates. Chapter 7 talks about the current trend in WPF development, the Model View View-Model (MVVM) framework. This is a well known pattern for connecting things interface to actions, and it is explained competently. A typical implementation is presented which also presents the command pattern used throughout WPF. A complete application using MVVM is presented from start to finish, including typical features such as undo. Style and layout is covered on chapter 8. Why/how to use styles, applying them automatically,  using the many types of triggers to change styles automatically, using Expression Blend behaviors and templates are all covered. Next chapter, 9, is about graphics and animations programming. It explains how to create shapes, transform common UI elements, apply special effects and perform simple animations. The following chapter, 10, is about creating custom controls, either by deriving from UserControl or from an existing control or framework element class, applying custom templates for changing the way the control looks. One useful example is a custom layout panel that arranges its children along a circumference. The final chapter, 11, is about multi-threading programming and how one can integrate it with WPF. Includes how to invoke methods and properties on WPF classes from threads other than the main UI, using background tasks and timers and even using the new C# 5.0 asynchronous operations. It’s an interesting book, like I said, mostly for newcomers. It provides a competent introduction to WPF, with examples that cover the most common scenarios and also give directions to more complex ones. I recommend it to everyone wishing to learn WPF.

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• JavaScript Browser Hacks

  Recently during one of my client side scripting classes, I was trying to show my students some basic examples of JavaScript as an introduction to the language.  My first basic example was to show an alert box using JavaScript via the address bar. The student’s reaction to my browser hack example really caught me off guard in a good way. After programming with a language for close to 10 years you start to lose the "Awe Cool!" effect that new learners of a language experience when writing code. New learns of JavaScript are the reason why I created this post. Please enjoy. Note: Place JavaScript in to address bar and then press the enter key. Example 1: JavaScript Alert box displaying My name: John Doe Javascript:alert('My name: \n John Doe') ; Example 2: JavaScript alert box displaying name entered by user. javascript:alert('My name: \n ' + prompt('Enter Name','Name')) ; Example 3: JavaScript alert box displaying name entered by user, and then displays the length of the name. javascript:var name= prompt('Enter Name','Name'); alert('My name: \n ' + name); alert(name.length); If you notice, the address bar will execute JavaScript on the current page loaded in the browser using the Document Object Model (DOM). Additionally, the address bar will allow multiple lines to be executed sequentially even though all of the code is contained within one line due to the fact that the JavaScript interpreter uses the “;” to indicate where a line of ends and a new one begins. After doing a little more research on the topic of JavaScript Browser Hacks I found a few other cool JavaScript hacks which I will list below. Example 4: Make any webpage editableSource: http://www.openjason.com/2008/09/02/browser-hack-make-any-web-page-editable/ javascript:document.body.contentEditable='true'; document.designMode='on'; void 0; Example 5: CHINESE DRAGON DANCING Source: http://nzeyi.wordpress.com/2009/06/01/dwrajaxjavascript-hacks-the-secrets-of-javascript-in-the-adress-bar/ javascript:R=0;x1=0.1;y1=0.05;x2=0.25;y2=0.24;x3=1.6; y3=0.24;x4=300;y4=200;x5=300;y5=200;DI=document.links; DIL=DI.length;A=function(){for(i=0;i-DIL;i++){DI[i].style. position='absolute';DI[i].style.left=Math.sin(R*x1+i*x2+x3)*x4+ x5;DI[i].style.top=Math.cos(R*y1+i*y2+y3)*y4+y5}R++;}; setInterval('A()',5);void(0); Example 6: Reveal content stored in password protected fields javascript:(function(){var s,F,j,f,i; s = “”; F = document.forms; for(j=0; j Example 7: Force user to close browser windowSource: http://forums.digitalpoint.com/showthread.php?t=767053 javascript:while(1){alert('Restart your brower to close this box!')} Learn more about JavaScript Browser Hacks.

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• JavaScript: this

  - by bdukes

  JavaScript is a language steeped in juxtaposition.  It was made to “look like Java,” yet is dynamic and classless.  From this origin, we get the new operator and the this keyword.  You are probably used to this referring to the current instance of a class, so what could it mean in a language without classes? In JavaScript, this refers to the object off of which a function is referenced when it is invoked (unless it is invoked via call or apply). What this means is that this is not bound to your function, and can change depending on how your function is invoked. It also means that this changes when declaring a function inside another function (i.e. each function has its own this), such as when writing a callback. Let's see some of this in action: var obj = { count: 0, increment: function () { this.count += 1; }, logAfterTimeout = function () { setTimeout(function () { console.log(this.count); }, 1); } }; obj.increment(); console.log(obj.count); // 1 var increment = obj.increment; window.count = 'global count value: '; increment(); console.log(obj.count); // 1 console.log(window.count); // global count value: 1 var newObj = {count:50}; increment.call(newObj); console.log(newObj.count); // 51 obj.logAfterTimeout();// global count value: 1 obj.logAfterTimeout = function () { var proxiedFunction = $.proxy(function () { console.log(this.count); }, this); setTimeout(proxiedFunction, 1); }; obj.logAfterTimeout(); // 1 obj.logAfterTimeout = function () { var that = this; setTimeout(function () { console.log(that.count); }, 1); }; obj.logAfterTimeout(); // 1 The last couple of examples here demonstrate some methods for making sure you get the values you expect.  The first time logAfterTimeout is redefined, we use jQuery.proxy to create a new function which has its this permanently set to the passed in value (in this case, the current this).  The second time logAfterTimeout is redefined, we save the value of this in a variable (named that in this case, also often named self) and use the new variable in place of this. Now, all of this is to clarify what’s going on when you use this.  However, it’s pretty easy to avoid using this altogether in your code (especially in the way I’ve demonstrated above).  Instead of using this.count all over the place, it would have been much easier if I’d made count a variable instead of a property, and then I wouldn’t have to use this to refer to it.  var obj = (function () { var count = 0; return { increment: function () { count += 1; }, logAfterTimeout = function () { setTimeout(function () { console.log(count); }, 1); }, getCount: function () { return count; } }; }()); If you’re writing your code in this way, the main place you’ll run into issues with this is when handling DOM events (where this is the element on which the event occurred).  In that case, just be careful when using a callback within that event handler, that you’re not expecting this to still refer to the element (and use proxy or that/self if you need to refer to it). Finally, as demonstrated in the example, you can use call or apply on a function to set its this value.  This isn’t often needed, but you may also want to know that you can use apply to pass in an array of arguments to a function (e.g. console.log.apply(console, [1, 2, 3, 4])).

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• FluentPath: a fluent wrapper around System.IO

  - by Bertrand Le Roy

  .NET is now more than eight years old, and some of its APIs got old with more grace than others. System.IO in particular has always been a little awkward. It’s mostly static method calls (Path.*, Directory.*, etc.) and some stateful classes (DirectoryInfo, FileInfo). In these APIs, paths are plain strings. Since .NET v1, lots of good things happened to C#: lambda expressions, extension methods, optional parameters to name just a few. Outside of .NET, other interesting things happened as well. For example, you might have heard about this JavaScript library that had some success introducing a fluent API to handle the hierarchical structure of the HTML DOM. You know? jQuery. Knowing all that, every time I need to use the stuff in System.IO, I cringe. So I thought I’d just build a more modern wrapper around it. I used a fluent API based on an essentially immutable Path type and an enumeration of such path objects. To achieve the fluent style, a healthy dose of lambda expressions is being used to act on the objects. Without further ado, here’s an example of what you can do with the new API. In that example, I’m using a Media Center extension that wants all video files to be in their own folder. For that, I need a small tool that creates directories for each video file and moves the files in there. Here’s the code for it: Path.Get(args[0]) .Select(p => p.Extension == ".avi" || p.Extension == ".m4v" || p.Extension == ".wmv" || p.Extension == ".mp4" || p.Extension == ".dvr-ms" || p.Extension == ".mpg" || p.Extension == ".mkv") .CreateDirectory(p => p.Parent .Combine(p.FileNameWithoutExtension)) .Previous() .Move(p => p.Parent .Combine(p.FileNameWithoutExtension) .Combine(p.FileName)); This code creates a Path object pointing at the path pointed to by the first command line argument of my executable. It then selects all video files. After that, it creates directories that have the same names as each of the files, but without their extension. The result of that operation is the set of created directories. We can now get back to the previous set using the Previous method, and finally we can move each of the files in the set to the corresponding freshly created directory, whose name is the combination of the parent directory and the filename without extension. The new fluent path library covers a fair part of what’s in System.IO in a single, convenient API. Check it out, I hope you’ll enjoy it. Suggestions are more than welcome. For example, should I make this its own project on CodePlex or is this informal style just OK? Anything missing that you’d like to see? Is there a specific example you’d like to see expressed with the new API? Bugs? The code can be downloaded from here (this is under a new BSD license): http://weblogs.asp.net/blogs/bleroy/Samples/FluentPath.zip

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• Optional Parameters and Named Arguments in C# 4 (and a cool scenario w/ ASP.NET MVC 2)

  - by ScottGu

  [In addition to blogging, I am also now using Twitter for quick updates and to share links. Follow me at: twitter.com/scottgu] This is the seventeenth in a series of blog posts I’m doing on the upcoming VS 2010 and .NET 4 release. Today’s post covers two new language feature being added to C# 4.0 – optional parameters and named arguments – as well as a cool way you can take advantage of optional parameters (both in VB and C#) with ASP.NET MVC 2. Optional Parameters in C# 4.0 C# 4.0 now supports using optional parameters with methods, constructors, and indexers (note: VB has supported optional parameters for awhile). Parameters are optional when a default value is specified as part of a declaration.  For example, the method below takes two parameters – a “category” string parameter, and a “pageIndex” integer parameter.  The “pageIndex” parameter has a default value of 0, and as such is an optional parameter: When calling the above method we can explicitly pass two parameters to it: Or we can omit passing the second optional parameter – in which case the default value of 0 will be passed:   Note that VS 2010’s Intellisense indicates when a parameter is optional, as well as what its default value is when statement completion is displayed: Named Arguments and Optional Parameters in C# 4.0 C# 4.0 also now supports the concept of “named arguments”.  This allows you to explicitly name an argument you are passing to a method – instead of just identifying it by argument position.  For example, I could write the code below to explicitly identify the second argument passed to the GetProductsByCategory method by name (making its usage a little more explicit): Named arguments come in very useful when a method supports multiple optional parameters, and you want to specify which arguments you are passing.  For example, below we have a method DoSomething that takes two optional parameters: We could use named arguments to call the above method in any of the below ways: Because both parameters are optional, in cases where only one (or zero) parameters is specified then the default value for any non-specified arguments is passed. ASP.NET MVC 2 and Optional Parameters One nice usage scenario where we can now take advantage of the optional parameter support of VB and C# is with ASP.NET MVC 2’s input binding support to Action methods on Controller classes. For example, consider a scenario where we want to map URLs like “Products/Browse/Beverages” or “Products/Browse/Deserts” to a controller action method.  We could do this by writing a URL routing rule that maps the URLs to a method like so: We could then optionally use a “page” querystring value to indicate whether or not the results displayed by the Browse method should be paged – and if so which page of the results should be displayed.  For example: /Products/Browse/Beverages?page=2. With ASP.NET MVC 1 you would typically handle this scenario by adding a “page” parameter to the action method and make it a nullable int (which means it will be null if the “page” querystring value is not present).  You could then write code like below to convert the nullable int to an int – and assign it a default value if it was not present in the querystring: With ASP.NET MVC 2 you can now take advantage of the optional parameter support in VB and C# to express this behavior more concisely and clearly.  Simply declare the action method parameter as an optional parameter with a default value: C# VB If the “page” value is present in the querystring (e.g. /Products/Browse/Beverages?page=22) then it will be passed to the action method as an integer.  If the “page” value is not in the querystring (e.g. /Products/Browse/Beverages) then the default value of 0 will be passed to the action method.  This makes the code a little more concise and readable. Summary There are a bunch of great new language features coming to both C# and VB with VS 2010.  The above two features (optional parameters and named parameters) are but two of them.  I’ll blog about more in the weeks and months ahead. If you are looking for a good book that summarizes all the language features in C# (including C# 4.0), as well provides a nice summary of the core .NET class libraries, you might also want to check out the newly released C# 4.0 in a Nutshell book from O’Reilly: It does a very nice job of packing a lot of content in an easy to search and find samples format. Hope this helps, Scott

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