mvc net - Page 42 - Developer IT

Providing or Filtering assemblies when registering areas for an ASP.NET MVC 2.0 application

- by HackedByChinese

I have a large application that currently exists as a hybrid of WebForms and MVC 2.0. Startup of my application is dreadful, and the culprit is primarily because of the AreaRegistration.RegisterAllAreas call. More specifically, that it is using the System.Web. Compilation.BuildManager.GetReferencedAssemblies to enumerate all types in assemblies directly referenced by the application and test them to see if they derive from AreaRegistration. Unfortunately, I have a number of third-party assemblies that happen to be quite extensive, so this initial load can be pretty bad. I'd have much better results if I could tell it which assemblies to look for AreaRegistrations, or even register areas manually for the time being. I can gather up all the internals of AreaRegistration to create and invoke the registration, but I'm just curious if others have had and worked around this issue.

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Avoiding the Controller with Routing Rules in ASP.NET MVC

- by Ryan Elkins

I've created a website with ASP.NET MVC. I have a number of static pages that I am currently serving through a single controller called Home. This creates some rather ugly URLs. example.com/Home/About example.com/Home/ContactUs example.com/Home/Features You get the idea. I'd rather not have to create a controller for each one of these as the actions simply call the View with no model being passed in. Is there a way to write a routing rule that will remove the controller from the URL? I'd like it to look like: example.com/About example.com/ContactUs example.com/Features If not, how is this situation normally handled? I imagine I'm not the first person to run in to this.

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ASP.NET MVC 2 - Account controller not found

- by Chris

Hi all, I've recently created an ASP.NET MVC 2 application, which works perfectly in the development environment. However, when I deploy it to the server (123-reg Premium Hosting), I can access all of the expected areas - except the Account controller (www.host.info/Account). This then attempts to redirect to the Error.aspx page (www.host.info/Shared/Error.aspx) which it cannot find. I've checked that all of the views have been published, and they're all in the correct place. It seems bizarre that two other controllers can be accessed with no problems, whereas the Account controller cannot be found. I have since renamed the AccountController to SecureController, and all of the dependencies, to no avail. The problem with not being able to find the Error.aspx page also occurs on the development environment. Any ideas would be greatly appreciated. Thanks, Chris

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how big should your controllers be in asp.net-mvc

- by ooo

i see the new feature of areas in asp.net-mvc 2. it got me thinking. why would i need this? i did some reading on the use cases and it came down to a specific point to me around how big and how broad scope should my controllers should be? should i try to have many little controllers? one big controller? how do people determine the sweet spot for number of controllers? i think mine are maybe too large (which had me questioning areas in the first place as maybe my controller name should really be an area and have a number of smaller controllers)

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Datamodel for a MVC learning project

- by Dofs

Hi, I am trying to learn Microsoft MVC 2, and have in that case found a small project I wanted to deploy it on. My idea was to simulate a restaurant where you can order a table. Basics: A user can only reserve a full table, so I don't have the trouble of merging people on different tables. A person can order a table for a certain amount of hours. My question was how I could make the data model the smartest way. I thought of just having a my database like this: Table { Id, TableName } Reservations { Id TableId ReservedFrom ReservedTo UserId } User { UserId UserName ... } By doing it this way I would have to program a lot of the logic in e.g. the business layer, to support which tables are occupied at what time, instead of having the data model handle it. Therefore do you guys have a better way to do this?

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Can't select View Content dropdown when adding view in MVC using Interfaces

- by fearofawhackplanet

I have my Model defined externally in two projects - a Core project and an Interface project. I am opening the Add View dialogue from my controller, and selecting Create a strongly typed view. In the drop down list, I can select the concrete types like MyProject.Model.Core.OrderDetails, but the interface types like MyProject.Model.Interface.IOrderDetails aren't there. I can type the interface class in manually and everything works, but then the View content menu that lets you select the Create, Delete, List, etc scaffolding is disabled. Is there some problem with using interfaces in MVC? Or is it something else I'm missing?

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How to validate two properties with ASP.NET MVC 2

- by CodeMonkey

Hey folks :-) I'm just getting started with ASP.NET MVC 2, and playing around with Validation. Let's say I have 2 properties: Password1 Password2 And I want to require that they are both filled in, and require that both are the same before the model is valid. I have a simple class called "NewUser". How would I implement that? I've read about ValidationAttribute, and understand that. But I don't see how I would use that to implement a validation that compares two or more properties against eathother. Thanks in advance!

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Routing Business Branches: Granular access control in ASP.NET MVC

- by FreshCode

How should ASP.NET MVC routes be structured to allow granular role-based access control to business branches? Every business entity is related to a branch, either by itself or via its parent entities. Is there an elegant way to authorize actions based on user-roles for any number of branches? 1. {branch} in route? {branch}/{controller}/{action}/{id} Action: [Authorize(Roles="Technician")] public ActionResult BusinessWidgetAction(BusinessObject obj) { // Authorize will test if User has Technician role in branch context // ... } 2. Retrieve branch from business entity? {controller}/{action}/{id} Action: public ActionResult BusinessWidgetAction(BusinessObject obj) { if (!User.HasAccessTo("WidgetAction", obj.Branch)) throw new HttpException(403, "No soup for you!"); // or redirect // ... } 3. Or is there a better way?

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ASP.NET MVC 2 - ViewData empty after POST

- by Alex

I don't really know where to look for an error... the situation: I have an ASPX view which contains a form and a few input's, and when I click the submit button everything is POST'ed to one of my ASP.NET MVC actions. When I set a breakpoint there, it is hit correctly. When I use FireBug to see what is sent to the action, I correctly see data1=abc&data2=something&data3=1234. However, nothing is arriving in my action method. ViewData is empty, there is no ViewData["data1"] or anything else that would show that data arrived. How can this be? Where can I start looking for the error?

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Modular enterprise architecture using MVC and Orchard CMS

- by MrJD

I'm making a large scale MVC application using Orchard. And I'm going to be separating my logic into modules. I'm also trying to heavily decouple the application for maximum extensibility and testability. I have a rudimentary understanding of IoC, Repository Pattern, Unit of Work pattern and Service Layer pattern. I've made myself a diagram. I'm wondering if it is correct and if there is anything I have missed regarding an extensible application. Note that each module is a separate project.

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Using javascript to call controller methond in mvc

- by Christian Thoresson Dahl

Im trying to make a table row work as a link to another view in my mvc website. Instead of using the standard "Details" link provided by the auto generated table list, I would like to use the table row as a link to the "Details" view instead. So somehow I need to make the row work as a link. Each rom has a unique id that I need to pass on to the controller method. I have tried different solutions but noting happens when I press on the table row... So far this is what I have: <script type="text/javascript"> $(document).ready(function(){ $('#customers tr').click(function () { var id = $(this).attr('id'); $.ajax({ url: "Customer/Details" + id, succes: function () { } }); }) }) </script> My controller method: public ActionResult Details(int id) { Customer model = new Customer(); model = this.dbEntities.Customers.Where(c => c.Customer_ID == id).Single(); return View(model); }

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Simple ASP.NET MVC Routing question

- by Robert

Hi there, I have two pages in my simple MVC App with two defined routes: routes.MapRoute( "Results", // Route name "Results/{id}", // URL with parameters new { controller = "Results", action = "Index", id = "" } // Parameter defaults ); routes.MapRoute( "Default", // Route name "{controller}/{action}/{id}", // URL with parameters new { controller = "Main", action = "Index", id = UrlParameter.Optional } // Parameter defaults ); I needed to have the results page load with just a product ID such as this: [MyDomain....]/Results/12345. But also the main page does a POST (using JQuery) to the Results Controller for updates using this route: [MyDomain....]/Main/Update along with a data bag. This works fine when I only have the "Default" route. But when I added the other "Results" route, all the POST calls to update are failing. Any ideas what I'm doing wrong??? Thanks a lot.

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MVC Custom Model Binder Binding Multiple Values

- by BMD86

Hello everyone, I have a scenario in which I have multiple sources to bind to my model. For one, I have a view tied to a strongly-typed model, but this scenario also entails posting data to this view from a 3rd party site. Essentially, what I believe I am after in the custom model binding is to investigate the form values in the Request object within HTTPContext to see if I have a field such as "postedFirstName". If so, I want to bind that value instead of the textbox "FirstName" in my view. I've done a good bit of searching but have not find anything that exactly addresses such a scenario. This link was close, I thought, but not quite: http://stackoverflow.com/questions/970335/asp-net-mvc-mixing-custom-and-default-model-binding Any input is greatly appreciated!

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Client Id for Property (ASP.Net MVC)

- by Felipe

Hi guys... I'm begginer in asp.net mvc, and i have a doubs: I'm trying to do a label for a TextBox in my View and I'd like to know, how can I take a Id that will be render in client to generete scripts... for example: <label for="<%=x.Name.?ClientId?%>"> Name: </label> <%=Html.TextBoxFor(x=>x.Name) %> What need I put in "?ClientId?" to make sure that correct Id will be render to the corresponding control ? Thanks Cheers

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Custom librairies with Razor with the release version of MVC 3

- by Maxim

So I'm developing an in-house library for MVC 3 and I want to add it to my project. I added it to my web.config. I added the assembly and added it to the pages - namespaces section and... no. Doesn't work. I tried recompiling, etc... but Razor doesn't like it at all. It's not an intellisense problem... the site can't run if I use my defined namespace. The only way that I made it work was by using the following statements: @using Sample.Helpers I don't want to use it in the pages. I want to be able to deploy it to many projects and adding it to the web.config is definitely the way to go. Anyone ran into this problem?

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[ASP.NET MVC] Problem with View - it does not refresh after db update

- by crocodillez

Hi, I am working with small ASP.NET MVC project - online store. I have addToCart method which adds selected product to cart - it updates cart table in my db and showing cart view with its content. But I have problems. while db is updating correctly the view does not. I see that quantity of the product in my db is incremented correctly but quantity in view is not changed. I have to stop debugging my app in visual studia and restart it - then my view is showing correct data. What can be wrong?

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Creating a dynamic proxy generator – Part 1 – Creating the Assembly builder, Module builder and cach

- by SeanMcAlinden

I’ve recently started a project with a few mates to learn the ins and outs of Dependency Injection, AOP and a number of other pretty crucial patterns of development as we’ve all been using these patterns for a while but have relied totally on third part solutions to do the magic. We thought it would be interesting to really get into the details by rolling our own IoC container and hopefully learn a lot on the way, and you never know, we might even create an excellent framework. The open source project is called Rapid IoC and is hosted at http://rapidioc.codeplex.com/ One of the most interesting tasks for me is creating the dynamic proxy generator for enabling Aspect Orientated Programming (AOP). In this series of articles, I’m going to track each step I take for creating the dynamic proxy generator and I’ll try my best to explain what everything means - mainly as I’ll be using Reflection.Emit to emit a fair amount of intermediate language code (IL) to create the proxy types at runtime which can be a little taxing to read. It’s worth noting that building the proxy is without a doubt going to be slightly painful so I imagine there will be plenty of areas I’ll need to change along the way. Anyway lets get started… Part 1 - Creating the Assembly builder, Module builder and caching mechanism Part 1 is going to be a really nice simple start, I’m just going to start by creating the assembly, module and type caches. The reason we need to create caches for the assembly, module and types is simply to save the overhead of recreating proxy types that have already been generated, this will be one of the important steps to ensure that the framework is fast… kind of important as we’re calling the IoC container ‘Rapid’ – will be a little bit embarrassing if we manage to create the slowest framework. The Assembly builder The assembly builder is what is used to create an assembly at runtime, we’re going to have two overloads, one will be for the actual use of the proxy generator, the other will be mainly for testing purposes as it will also save the assembly so we can use Reflector to examine the code that has been created. Here’s the code: DynamicAssemblyBuilder using System; using System.Reflection; using System.Reflection.Emit; namespace Rapid.DynamicProxy.Assembly { /// <summary> /// Class for creating an assembly builder. /// </summary> internal static class DynamicAssemblyBuilder { #region Create /// <summary> /// Creates an assembly builder. /// </summary> /// <param name="assemblyName">Name of the assembly.</param> public static AssemblyBuilder Create(string assemblyName) { AssemblyName name = new AssemblyName(assemblyName); AssemblyBuilder assembly = AppDomain.CurrentDomain.DefineDynamicAssembly( name, AssemblyBuilderAccess.Run); DynamicAssemblyCache.Add(assembly); return assembly; } /// <summary> /// Creates an assembly builder and saves the assembly to the passed in location. /// </summary> /// <param name="assemblyName">Name of the assembly.</param> /// <param name="filePath">The file path.</param> public static AssemblyBuilder Create(string assemblyName, string filePath) { AssemblyName name = new AssemblyName(assemblyName); AssemblyBuilder assembly = AppDomain.CurrentDomain.DefineDynamicAssembly( name, AssemblyBuilderAccess.RunAndSave, filePath); DynamicAssemblyCache.Add(assembly); return assembly; } #endregion } } So hopefully the above class is fairly explanatory, an AssemblyName is created using the passed in string for the actual name of the assembly. An AssemblyBuilder is then constructed with the current AppDomain and depending on the overload used, it is either just run in the current context or it is set up ready for saving. It is then added to the cache. DynamicAssemblyCache using System.Reflection.Emit; using Rapid.DynamicProxy.Exceptions; using Rapid.DynamicProxy.Resources.Exceptions; namespace Rapid.DynamicProxy.Assembly { /// <summary> /// Cache for storing the dynamic assembly builder. /// </summary> internal static class DynamicAssemblyCache { #region Declarations private static object syncRoot = new object(); internal static AssemblyBuilder Cache = null; #endregion #region Adds a dynamic assembly to the cache. /// <summary> /// Adds a dynamic assembly builder to the cache. /// </summary> /// <param name="assemblyBuilder">The assembly builder.</param> public static void Add(AssemblyBuilder assemblyBuilder) { lock (syncRoot) { Cache = assemblyBuilder; } } #endregion #region Gets the cached assembly /// <summary> /// Gets the cached assembly builder. /// </summary> /// <returns></returns> public static AssemblyBuilder Get { get { lock (syncRoot) { if (Cache != null) { return Cache; } } throw new RapidDynamicProxyAssertionException(AssertionResources.NoAssemblyInCache); } } #endregion } } The cache is simply a static property that will store the AssemblyBuilder (I know it’s a little weird that I’ve made it public, this is for testing purposes, I know that’s a bad excuse but hey…) There are two methods for using the cache – Add and Get, these just provide thread safe access to the cache. The Module Builder The module builder is required as the create proxy classes will need to live inside a module within the assembly. Here’s the code: DynamicModuleBuilder using System.Reflection.Emit; using Rapid.DynamicProxy.Assembly; namespace Rapid.DynamicProxy.Module { /// <summary> /// Class for creating a module builder. /// </summary> internal static class DynamicModuleBuilder { /// <summary> /// Creates a module builder using the cached assembly. /// </summary> public static ModuleBuilder Create() { string assemblyName = DynamicAssemblyCache.Get.GetName().Name; ModuleBuilder moduleBuilder = DynamicAssemblyCache.Get.DefineDynamicModule (assemblyName, string.Format("{0}.dll", assemblyName)); DynamicModuleCache.Add(moduleBuilder); return moduleBuilder; } } } As you can see, the module builder is created on the assembly that lives in the DynamicAssemblyCache, the module is given the assembly name and also a string representing the filename if the assembly is to be saved. It is then added to the DynamicModuleCache. DynamicModuleCache using System.Reflection.Emit; using Rapid.DynamicProxy.Exceptions; using Rapid.DynamicProxy.Resources.Exceptions; namespace Rapid.DynamicProxy.Module { /// <summary> /// Class for storing the module builder. /// </summary> internal static class DynamicModuleCache { #region Declarations private static object syncRoot = new object(); internal static ModuleBuilder Cache = null; #endregion #region Add /// <summary> /// Adds a dynamic module builder to the cache. /// </summary> /// <param name="moduleBuilder">The module builder.</param> public static void Add(ModuleBuilder moduleBuilder) { lock (syncRoot) { Cache = moduleBuilder; } } #endregion #region Get /// <summary> /// Gets the cached module builder. /// </summary> /// <returns></returns> public static ModuleBuilder Get { get { lock (syncRoot) { if (Cache != null) { return Cache; } } throw new RapidDynamicProxyAssertionException(AssertionResources.NoModuleInCache); } } #endregion } } The DynamicModuleCache is very similar to the assembly cache, it is simply a statically stored module with thread safe Add and Get methods. The DynamicTypeCache To end off this post, I’m going to create the cache for storing the generated proxy classes. I’ve spent a fair amount of time thinking about the type of collection I should use to store the types and have finally decided that for the time being I’m going to use a generic dictionary. This may change when I can actually performance test the proxy generator but the time being I think it makes good sense in theory, mainly as it pretty much maintains it’s performance with varying numbers of items – almost constant (0)1. Plus I won’t ever need to loop through the items which is not the dictionaries strong point. Here’s the code as it currently stands: DynamicTypeCache using System; using System.Collections.Generic; using System.Security.Cryptography; using System.Text; namespace Rapid.DynamicProxy.Types { /// <summary> /// Cache for storing proxy types. /// </summary> internal static class DynamicTypeCache { #region Declarations static object syncRoot = new object(); public static Dictionary<string, Type> Cache = new Dictionary<string, Type>(); #endregion /// <summary> /// Adds a proxy to the type cache. /// </summary> /// <param name="type">The type.</param> /// <param name="proxy">The proxy.</param> public static void AddProxyForType(Type type, Type proxy) { lock (syncRoot) { Cache.Add(GetHashCode(type.AssemblyQualifiedName), proxy); } } /// <summary> /// Tries the type of the get proxy for. /// </summary> /// <param name="type">The type.</param> /// <returns></returns> public static Type TryGetProxyForType(Type type) { lock (syncRoot) { Type proxyType; Cache.TryGetValue(GetHashCode(type.AssemblyQualifiedName), out proxyType); return proxyType; } } #region Private Methods private static string GetHashCode(string fullName) { SHA1CryptoServiceProvider provider = new SHA1CryptoServiceProvider(); Byte[] buffer = Encoding.UTF8.GetBytes(fullName); Byte[] hash = provider.ComputeHash(buffer, 0, buffer.Length); return Convert.ToBase64String(hash); } #endregion } } As you can see, there are two public methods, one for adding to the cache and one for getting from the cache. Hopefully they should be clear enough, the Get is a TryGet as I do not want the dictionary to throw an exception if a proxy doesn’t exist within the cache. Other than that I’ve decided to create a key using the SHA1CryptoServiceProvider, this may change but my initial though is the SHA1 algorithm is pretty fast to put together using the provider and it is also very unlikely to have any hashing collisions. (there are some maths behind how unlikely this is – here’s the wiki if you’re interested http://en.wikipedia.org/wiki/SHA_hash_functions) Anyway, that’s the end of part 1 – although I haven’t started any of the fun stuff (by fun I mean hairpulling, teeth grating Relfection.Emit style fun), I’ve got the basis of the DynamicProxy in place so all we have to worry about now is creating the types, interceptor classes, method invocation information classes and finally a really nice fluent interface that will abstract all of the hard-core craziness away and leave us with a lightning fast, easy to use AOP framework. Hope you find the series interesting. All of the source code can be viewed and/or downloaded at our codeplex site - http://rapidioc.codeplex.com/ Kind Regards, Sean.

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Parallelism in .NET – Part 1, Decomposition

- by Reed

The first step in designing any parallelized system is Decomposition. Decomposition is nothing more than taking a problem space and breaking it into discrete parts. When we want to work in parallel, we need to have at least two separate things that we are trying to run. We do this by taking our problem and decomposing it into parts. There are two common abstractions that are useful when discussing parallel decomposition: Data Decomposition and Task Decomposition. These two abstractions allow us to think about our problem in a way that helps leads us to correct decision making in terms of the algorithms we’ll use to parallelize our routine. To start, I will make a couple of minor points. I’d like to stress that Decomposition has nothing to do with specific algorithms or techniques. It’s about how you approach and think about the problem, not how you solve the problem using a specific tool, technique, or library. Decomposing the problem is about constructing the appropriate mental model: once this is done, you can choose the appropriate design and tools, which is a subject for future posts. Decomposition, being unrelated to tools or specific techniques, is not specific to .NET in any way. This should be the first step to parallelizing a problem, and is valid using any framework, language, or toolset. However, this gives us a starting point – without a proper understanding of decomposition, it is difficult to understand the proper usage of specific classes and tools within the .NET framework. Data Decomposition is often the simpler abstraction to use when trying to parallelize a routine. In order to decompose our problem domain by data, we take our entire set of data and break it into smaller, discrete portions, or chunks. We then work on each chunk in the data set in parallel. This is particularly useful if we can process each element of data independently of the rest of the data. In a situation like this, there are some wonderfully simple techniques we can use to take advantage of our data. By decomposing our domain by data, we can very simply parallelize our routines. In general, we, as developers, should be always searching for data that can be decomposed. Finding data to decompose if fairly simple, in many instances. Data decomposition is typically used with collections of data. Any time you have a collection of items, and you’re going to perform work on or with each of the items, you potentially have a situation where parallelism can be exploited. This is fairly easy to do in practice: look for iteration statements in your code, such as for and foreach. Granted, every for loop is not a candidate to be parallelized. If the collection is being modified as it’s iterated, or the processing of elements depends on other elements, the iteration block may need to be processed in serial. However, if this is not the case, data decomposition may be possible. Let’s look at one example of how we might use data decomposition. Suppose we were working with an image, and we were applying a simple contrast stretching filter. When we go to apply the filter, once we know the minimum and maximum values, we can apply this to each pixel independently of the other pixels. This means that we can easily decompose this problem based off data – we will do the same operation, in parallel, on individual chunks of data (each pixel). Task Decomposition, on the other hand, is focused on the individual tasks that need to be performed instead of focusing on the data. In order to decompose our problem domain by tasks, we need to think about our algorithm in terms of discrete operations, or tasks, which can then later be parallelized. Task decomposition, in practice, can be a bit more tricky than data decomposition. Here, we need to look at what our algorithm actually does, and how it performs its actions. Once we have all of the basic steps taken into account, we can try to analyze them and determine whether there are any constraints in terms of shared data or ordering. There are no simple things to look for in terms of finding tasks we can decompose for parallelism; every algorithm is unique in terms of its tasks, so every algorithm will have unique opportunities for task decomposition. For example, say we want our software to perform some customized actions on startup, prior to showing our main screen. Perhaps we want to check for proper licensing, notify the user if the license is not valid, and also check for updates to the program. Once we verify the license, and that there are no updates, we’ll start normally. In this case, we can decompose this problem into tasks – we have a few tasks, but there are at least two discrete, independent tasks (check licensing, check for updates) which we can perform in parallel. Once those are completed, we will continue on with our other tasks. One final note – Data Decomposition and Task Decomposition are not mutually exclusive. Often, you’ll mix the two approaches while trying to parallelize a single routine. It’s possible to decompose your problem based off data, then further decompose the processing of each element of data based on tasks. This just provides a framework for thinking about our algorithms, and for discussing the problem.

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Getting Started With Knockout.js

- by Pawan_Mishra

Client side template binding in web applications is getting popular with every passing day. More and more libraries are coming up with enhanced support for client side binding. jQuery templates is one very popular mechanism for client side template bindings. The idea with client side template binding is simple. Define the html mark-up with appropriate place holder for data. User template engines like jQuery template to bind the data(JSON formatted data) with the previously defined mark-up.In this...(read more)

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.NET: Interface Problem VB.net Getter Only Interface

- by snmcdonald

Why does an interface override a class definition and violate class encapsulation? I have included two samples below, one in C# and one in VB.net? VB.net Module Module1 Sub Main() Dim testInterface As ITest = New TestMe Console.WriteLine(testInterface.Testable) ''// Prints False testInterface.Testable = True ''// Access to Private!!! Console.WriteLine(testInterface.Testable) ''// Prints True Dim testClass As TestMe = New TestMe Console.WriteLine(testClass.Testable) ''// Prints False ''//testClass.Testable = True ''// Compile Error Console.WriteLine(testClass.Testable) ''// Prints False End Sub End Module Public Class TestMe : Implements ITest Private m_testable As Boolean = False Public Property Testable As Boolean Implements ITest.Testable Get Return m_testable End Get Private Set(ByVal value As Boolean) m_testable = value End Set End Property End Class Interface ITest Property Testable As Boolean End Interface C# using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace InterfaceCSTest { class Program { static void Main(string[] args) { ITest testInterface = new TestMe(); Console.WriteLine(testInterface.Testable); testInterface.Testable = true; Console.WriteLine(testInterface.Testable); TestMe testClass = new TestMe(); Console.WriteLine(testClass.Testable); //testClass.Testable = true; Console.WriteLine(testClass.Testable); } } class TestMe : ITest { private bool m_testable = false; public bool Testable { get { return m_testable; } private set { m_testable = value; } } } interface ITest { bool Testable { get; set; } } } More Specifically How do I implement a interface in VB.net that will allow for a private setter. For example in C# I can declare: class TestMe : ITest { private bool m_testable = false; public bool Testable { get { return m_testable; } private set //No Compile Error here! { m_testable = value; } } } interface ITest { bool Testable { get; } } However, if I declare an interface property as readonly in VB.net I cannot create a setter. If I create a VB.net interface as just a plain old property then interface declarations will violate my encapsulation. Public Class TestMe : Implements ITest Private m_testable As Boolean = False Public ReadOnly Property Testable As Boolean Implements ITest.Testable Get Return m_testable End Get Private Set(ByVal value As Boolean) ''//Compile Error m_testable = value End Set End Property End Class Interface ITest ReadOnly Property Testable As Boolean End Interface So my question is, how do I define a getter only Interface in VB.net with proper encapsulation? I figured the first example would have been the best method. However, it appears as if interface definitions overrule class definitions. So I tried to create a getter only (Readonly) property like in C# but it does not work for VB.net. Maybe this is just a limitation of the language?

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ASP.NET MVC + MySql Membership Provider, user cannot login

- by Jason Miesionczek

Hello, I've been playing around with using MySql as the membership provider for asp.net mvc forms authentication. I've got things configured correctly as far as i can tell, and i can create users via both the register action and asp.net web config site. however, when i try to login with one of the users, it does not work. it returns an error as if i had entered a wrong password, or if the account doesn't exist. i have verified in the database that the account does exist. I've followed the instructions here for reference: http://blog.tchami.com/post/ASPNET-MVC-2-and-MySQL-Membership-Provider.aspx here is my web.config: <?xml version="1.0"?>  <configuration> <connectionStrings> <add name="MySQLConn" connectionString="Server=localhost;Database=intereditor;Uid=<user>;Pwd=<password>;"/> </connectionStrings> <system.web> <compilation debug="true" targetFramework="4.0"> <assemblies> <add assembly="System.Web.Abstractions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" /> <add assembly="System.Web.Routing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" /> <add assembly="System.Web.Mvc, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" /> </assemblies> </compilation> <authentication mode="Forms"> <forms loginUrl="~/Account/LogOn" timeout="2880" name=".ASPXFORM$" path="/" requireSSL="false" slidingExpiration="true" enableCrossAppRedirects="false" /> </authentication> <membership defaultProvider="MySqlMembershipProvider"> <providers> <clear/> <add name="MySqlMembershipProvider" type="MySql.Web.Security.MySQLMembershipProvider,MySql.Web,Version=6.3.4.0, Culture=neutral,PublicKeyToken=c5687fc88969c44d" autogenerateschema="true" connectionStringName="MySQLConn" enablePasswordRetrieval="false" enablePasswordReset="true" requiresQuestionAndAnswer="false" requiresUniqueEmail="false" passwordFormat="Hashed" maxInvalidPasswordAttempts="5" minRequiredPasswordLength="6" minRequiredNonalphanumericCharacters="0" passwordAttemptWindow="10" passwordStrengthRegularExpression="" applicationName="/" /> </providers> </membership> <profile defaultProvider="MySqlProfileProvider"> <providers> <clear/> <add name="MySqlProfileProvider" type="MySql.Web.Profile.MySQLProfileProvider,MySql.Web,Version=6.3.4.0,Culture=neutral,PublicKeyToken=c5687fc88969c44d" connectionStringName="MySQLConn" applicationName="/" /> </providers> </profile> <roleManager enabled="true" defaultProvider="MySqlRoleProvider"> <providers> <clear /> <add name="MySqlRoleProvider" type="MySql.Web.Security.MySQLRoleProvider,MySql.Web,Version=6.3.4.0,Culture=neutral,PublicKeyToken=c5687fc88969c44d" connectionStringName="MySQLConn" applicationName="/" /> </providers> </roleManager> <pages> <namespaces> <add namespace="System.Web.Mvc" /> <add namespace="System.Web.Mvc.Ajax" /> <add namespace="System.Web.Mvc.Html" /> <add namespace="System.Web.Routing" /> </namespaces> </pages> </system.web> <system.webServer> <validation validateIntegratedModeConfiguration="false"/> <modules runAllManagedModulesForAllRequests="true"/> </system.webServer> <runtime> <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1"> <dependentAssembly> <assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" /> <bindingRedirect oldVersion="1.0.0.0" newVersion="2.0.0.0" /> </dependentAssembly> </assemblyBinding> </runtime> </configuration> Can anyone please help me identify what is wrong so that users can login? UPDATE So after debugging the login process in the code of the membership provider itself, i discovered that there is a bug in the provider. There is a discrepancy between the password hash that is stored in the database, and the has that is generated based on the inputted password. As a workaround for my issue, i changed the password format to 'encrpyted' and added a machine key to my web.config. I am still interested in figuring out the issue with the hashed format in the provider, and will spend some more time debugging it, and if i can figure out the problem, i will put together a patch and submit it.

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NullReferenceException makes me want to shoot myself

- by rockinthesixstring

Ok, so once upon a time, my code worked. Since then I did some refactoring (basic stuff so I thought) but now I'm getting a null reference exception, and I can't bloody well figure out why. Here's where it starts. note, this is the logout method, but all of my ActivityLogs sections are throwing this error Function LogOut(ByVal go As String) As ActionResult ActivityLogService.AddActivity(AuthenticationHelper.RetrieveAuthUser.ID, _ IActivityLogService.LogType.UserLogout, _ HttpContext.Request.UserHostAddress) ActivityLogService.SubmitChanges() ''# more stuff happens after this End Function The service is pretty straight forward (notice the ERROR THROWN HERE) Public Sub AddActivity(ByVal userid As Integer, ByVal activity As Integer, ByVal ip As String) Implements IActivityLogService.AddActivity Dim _activity As ActivityLog = New ActivityLog With {.Activity = activity, .UserID = userid, .UserIP = ip.IPAddressToNumber, .ActivityDate = DateTime.UtcNow} ActivityLogRepository.Create(_activity) ''#ERROR THROWN HERE End Sub And the Interface that the Service uses looks like this Public Interface IActivityLogService Sub AddActivity(ByVal userid As Integer, ByVal activity As Integer, ByVal ip As String) Function GetUsersLastActivity(ByVal UserID As Integer) As ActivityLog Sub SubmitChanges() ''' <summary> ''' The type of activity done by the user ''' </summary> ''' <remarks>Each int refers to an activity. ''' There can be no duplicates or modifications ''' after this application goes live</remarks> Enum LogType As Integer ''' <summary> ''' A new session started ''' </summary> SessionStarted = 1 ''' <summary> ''' A new user is Added/Created ''' </summary> UserAdded = 2 ''' <summary> ''' User has updated their profile ''' </summary> UserUpdated = 3 ''' <summary> ''' User has logged into they system ''' </summary> UserLogin = 4 ''' <summary> ''' User has logged out of the system ''' </summary> UserLogout = 5 ''' <summary> ''' A new event has been added ''' </summary> EventAdded = 6 ''' <summary> ''' An event has been updated ''' </summary> EventUpdated = 7 ''' <summary> ''' An event has been deleted ''' </summary> EventDeleted = 8 ''' <summary> ''' An event has received a Up/Down vote ''' </summary> EventVoted = 9 ''' <summary> ''' An event has been closed ''' </summary> EventCloseVoted = 10 ''' <summary> ''' A comment has been added to an event ''' </summary> CommentAdded = 11 ''' <summary> ''' A comment has been updated ''' </summary> CommentUpdated = 12 ''' <summary> ''' A comment has been deleted ''' </summary> CommentDeleted = 13 ''' <summary> ''' An event or comment has been reported as spam ''' </summary> SpamReported = 14 End Enum End Interface And the repository is equally straight forward Public Sub Create(ByVal activity As ActivityLog) Implements IActivityLogRepository.Create dc.ActivityLogs.InsertOnSubmit(activity) End Sub The stack trace is as follows [NullReferenceException: Object reference not set to an instance of an object.] MyApp.Core.Domain.ActivityLogService.AddActivity(Int32 userid, Int32 activity, String ip) in E:\Projects\MyApp\MyApp.Core\Domain\Services\ActivityLogService.vb:49 MyApp.Core.Controllers.UsersController.Authenticate(String go) in E:\Projects\MyApp\MyApp.Core\Controllers\UsersController.vb:258 lambda_method(Closure , ControllerBase , Object[] ) +163 System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters) +51 System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary2 parameters) +409 System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary2 parameters) +52 System.Web.Mvc.<c_DisplayClass15.b_12() +127 System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func1 continuation) +436 System.Web.Mvc.<>c__DisplayClass17.<InvokeActionMethodWithFilters>b__14() +61 System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList1 filters, ActionDescriptor actionDescriptor, IDictionary2 parameters) +305 System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +830 System.Web.Mvc.Controller.ExecuteCore() +136 System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +232 System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +39 System.Web.Mvc.<>c__DisplayClassb.<BeginProcessRequest>b__5() +68 System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +44 System.Web.Mvc.Async.<>c__DisplayClass81.b__7(IAsyncResult ) +42 System.Web.Mvc.Async.WrappedAsyncResult`1.End() +141 System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +54 System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +40 System.Web.Mvc.<c_DisplayClasse.b_d() +61 System.Web.Mvc.SecurityUtil.b_0(Action f) +31 System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action) +56 System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +110 System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +38 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +690 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +194 here's an image of the error when attached to the debugger. And here's an image of the DB schema in question Can anyone shed some light on what I might be missing here?

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Parallelism in .NET – Part 10, Cancellation in PLINQ and the Parallel class

- by Reed

Many routines are parallelized because they are long running processes. When writing an algorithm that will run for a long period of time, its typically a good practice to allow that routine to be cancelled. I previously discussed terminating a parallel loop from within, but have not demonstrated how a routine can be cancelled from the caller’s perspective. Cancellation in PLINQ and the Task Parallel Library is handled through a new, unified cooperative cancellation model introduced with .NET 4.0. Cancellation in .NET 4 is based around a new, lightweight struct called CancellationToken. A CancellationToken is a small, thread-safe value type which is generated via a CancellationTokenSource. There are many goals which led to this design. For our purposes, we will focus on a couple of specific design decisions: Cancellation is cooperative. A calling method can request a cancellation, but it’s up to the processing routine to terminate – it is not forced. Cancellation is consistent. A single method call requests a cancellation on every copied CancellationToken in the routine. Let’s begin by looking at how we can cancel a PLINQ query. Supposed we wanted to provide the option to cancel our query from Part 6: double min = collection .AsParallel() .Min(item => item.PerformComputation()); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } We would rewrite this to allow for cancellation by adding a call to ParallelEnumerable.WithCancellation as follows: var cts = new CancellationTokenSource(); // Pass cts here to a routine that could, // in parallel, request a cancellation try { double min = collection .AsParallel() .WithCancellation(cts.Token) .Min(item => item.PerformComputation()); } catch (OperationCanceledException e) { // Query was cancelled before it finished } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Here, if the user calls cts.Cancel() before the PLINQ query completes, the query will stop processing, and an OperationCanceledException will be raised. Be aware, however, that cancellation will not be instantaneous. When cts.Cancel() is called, the query will only stop after the current item.PerformComputation() elements all finish processing. cts.Cancel() will prevent PLINQ from scheduling a new task for a new element, but will not stop items which are currently being processed. This goes back to the first goal I mentioned – Cancellation is cooperative. Here, we’re requesting the cancellation, but it’s up to PLINQ to terminate. If we wanted to allow cancellation to occur within our routine, we would need to change our routine to accept a CancellationToken, and modify it to handle this specific case: public void PerformComputation(CancellationToken token) { for (int i=0; i<this.iterations; ++i) { // Add a check to see if we've been canceled // If a cancel was requested, we'll throw here token.ThrowIfCancellationRequested(); // Do our processing now this.RunIteration(i); } } With this overload of PerformComputation, each internal iteration checks to see if a cancellation request was made, and will throw an OperationCanceledException at that point, instead of waiting until the method returns. This is good, since it allows us, as developers, to plan for cancellation, and terminate our routine in a clean, safe state. This is handled by changing our PLINQ query to: try { double min = collection .AsParallel() .WithCancellation(cts.Token) .Min(item => item.PerformComputation(cts.Token)); } catch (OperationCanceledException e) { // Query was cancelled before it finished } PLINQ is very good about handling this exception, as well. There is a very good chance that multiple items will raise this exception, since the entire purpose of PLINQ is to have multiple items be processed concurrently. PLINQ will take all of the OperationCanceledException instances raised within these methods, and merge them into a single OperationCanceledException in the call stack. This is done internally because we added the call to ParallelEnumerable.WithCancellation. If, however, a different exception is raised by any of the elements, the OperationCanceledException as well as the other Exception will be merged into a single AggregateException. The Task Parallel Library uses the same cancellation model, as well. Here, we supply our CancellationToken as part of the configuration. The ParallelOptions class contains a property for the CancellationToken. This allows us to cancel a Parallel.For or Parallel.ForEach routine in a very similar manner to our PLINQ query. As an example, we could rewrite our Parallel.ForEach loop from Part 2 to support cancellation by changing it to: try { var cts = new CancellationTokenSource(); var options = new ParallelOptions() { CancellationToken = cts.Token }; Parallel.ForEach(customers, options, customer => { // Run some process that takes some time... DateTime lastContact = theStore.GetLastContact(customer); TimeSpan timeSinceContact = DateTime.Now - lastContact; // Check for cancellation here options.CancellationToken.ThrowIfCancellationRequested(); // If it's been more than two weeks, send an email, and update... if (timeSinceContact.Days > 14) { theStore.EmailCustomer(customer); customer.LastEmailContact = DateTime.Now; } }); } catch (OperationCanceledException e) { // The loop was cancelled } Notice that here we use the same approach taken in PLINQ. The Task Parallel Library will automatically handle our cancellation in the same manner as PLINQ, providing a clean, unified model for cancellation of any parallel routine. The TPL performs the same aggregation of the cancellation exceptions as PLINQ, as well, which is why a single exception handler for OperationCanceledException will cleanly handle this scenario. This works because we’re using the same CancellationToken provided in the ParallelOptions. If a different exception was thrown by one thread, or a CancellationToken from a different CancellationTokenSource was used to raise our exception, we would instead receive all of our individual exceptions merged into one AggregateException.

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Parallelism in .NET – Part 15, Making Tasks Run: The TaskScheduler

- by Reed

In my introduction to the Task class, I specifically made mention that the Task class does not directly provide it’s own execution. In addition, I made a strong point that the Task class itself is not directly related to threads or multithreading. Rather, the Task class is used to implement our decomposition of tasks. Once we’ve implemented our tasks, we need to execute them. In the Task Parallel Library, the execution of Tasks is handled via an instance of the TaskScheduler class. The TaskScheduler class is an abstract class which provides a single function: it schedules the tasks and executes them within an appropriate context. This class is the class which actually runs individual Task instances. The .NET Framework provides two (internal) implementations of the TaskScheduler class. Since a Task, based on our decomposition, should be a self-contained piece of code, parallel execution makes sense when executing tasks. The default implementation of the TaskScheduler class, and the one most often used, is based on the ThreadPool. This can be retrieved via the TaskScheduler.Default property, and is, by default, what is used when we just start a Task instance with Task.Start(). Normally, when a Task is started by the default TaskScheduler, the task will be treated as a single work item, and run on a ThreadPool thread. This pools tasks, and provides Task instances all of the advantages of the ThreadPool, including thread pooling for reduced resource usage, and an upper cap on the number of work items. In addition, .NET 4 brings us a much improved thread pool, providing work stealing and reduced locking within the thread pool queues. By using the default TaskScheduler, our Tasks are run asynchronously on the ThreadPool. There is one notable exception to my above statements when using the default TaskScheduler. If a Task is created with the TaskCreationOptions set to TaskCreationOptions.LongRunning, the default TaskScheduler will generate a new thread for that Task, at least in the current implementation. This is useful for Tasks which will persist for most of the lifetime of your application, since it prevents your Task from starving the ThreadPool of one of it’s work threads. The Task Parallel Library provides one other implementation of the TaskScheduler class. In addition to providing a way to schedule tasks on the ThreadPool, the framework allows you to create a TaskScheduler which works within a specified SynchronizationContext. This scheduler can be retrieved within a thread that provides a valid SynchronizationContext by calling the TaskScheduler.FromCurrentSynchronizationContext() method. This implementation of TaskScheduler is intended for use with user interface development. Windows Forms and Windows Presentation Foundation both require any access to user interface controls to occur on the same thread that created the control. For example, if you want to set the text within a Windows Forms TextBox, and you’re working on a background thread, that UI call must be marshaled back onto the UI thread. The most common way this is handled depends on the framework being used. In Windows Forms, Control.Invoke or Control.BeginInvoke is most often used. In WPF, the equivelent calls are Dispatcher.Invoke or Dispatcher.BeginInvoke. As an example, say we’re working on a background thread, and we want to update a TextBlock in our user interface with a status label. The code would typically look something like: // Within background thread work... string status = GetUpdatedStatus(); Dispatcher.BeginInvoke(DispatcherPriority.Normal, new Action( () => { statusLabel.Text = status; })); // Continue on in background method .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This works fine, but forces your method to take a dependency on WPF or Windows Forms. There is an alternative option, however. Both Windows Forms and WPF, when initialized, setup a SynchronizationContext in their thread, which is available on the UI thread via the SynchronizationContext.Current property. This context is used by classes such as BackgroundWorker to marshal calls back onto the UI thread in a framework-agnostic manner. The Task Parallel Library provides the same functionality via the TaskScheduler.FromCurrentSynchronizationContext() method. When setting up our Tasks, as long as we’re working on the UI thread, we can construct a TaskScheduler via: TaskScheduler uiScheduler = TaskScheduler.FromCurrentSynchronizationContext(); We then can use this scheduler on any thread to marshal data back onto the UI thread. For example, our code above can then be rewritten as: string status = GetUpdatedStatus(); (new Task(() => { statusLabel.Text = status; })) .Start(uiScheduler); // Continue on in background method This is nice since it allows us to write code that isn’t tied to Windows Forms or WPF, but is still fully functional with those technologies. I’ll discuss even more uses for the SynchronizationContext based TaskScheduler when I demonstrate task continuations, but even without continuations, this is a very useful construct. In addition to the two implementations provided by the Task Parallel Library, it is possible to implement your own TaskScheduler. The ParallelExtensionsExtras project within the Samples for Parallel Programming provides nine sample TaskScheduler implementations. These include schedulers which restrict the maximum number of concurrent tasks, run tasks on a single threaded apartment thread, use a new thread per task, and more.

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Parallelism in .NET – Part 18, Task Continuations with Multiple Tasks

- by Reed

In my introduction to Task continuations I demonstrated how the Task class provides a more expressive alternative to traditional callbacks. Task continuations provide a much cleaner syntax to traditional callbacks, but there are other reasons to switch to using continuations… Task continuations provide a clean syntax, and a very simple, elegant means of synchronizing asynchronous method results with the user interface. In addition, continuations provide a very simple, elegant means of working with collections of tasks. Prior to .NET 4, working with multiple related asynchronous method calls was very tricky. If, for example, we wanted to run two asynchronous operations, followed by a single method call which we wanted to run when the first two methods completed, we’d have to program all of the handling ourselves. We would likely need to take some approach such as using a shared callback which synchronized against a common variable, or using a WaitHandle shared within the callbacks to allow one to wait for the second. Although this could be accomplished easily enough, it requires manually placing this handling into every algorithm which requires this form of blocking. This is error prone, difficult, and can easily lead to subtle bugs. Similar to how the Task class static methods providing a way to block until multiple tasks have completed, TaskFactory contains static methods which allow a continuation to be scheduled upon the completion of multiple tasks: TaskFactory.ContinueWhenAll. This allows you to easily specify a single delegate to run when a collection of tasks has completed. For example, suppose we have a class which fetches data from the network. This can be a long running operation, and potentially fail in certain situations, such as a server being down. As a result, we have three separate servers which we will “query” for our information. Now, suppose we want to grab data from all three servers, and verify that the results are the same from all three. With traditional asynchronous programming in .NET, this would require using three separate callbacks, and managing the synchronization between the various operations ourselves. The Task and TaskFactory classes simplify this for us, allowing us to write: var server1 = Task.Factory.StartNew( () => networkClass.GetResults(firstServer) ); var server2 = Task.Factory.StartNew( () => networkClass.GetResults(secondServer) ); var server3 = Task.Factory.StartNew( () => networkClass.GetResults(thirdServer) ); var result = Task.Factory.ContinueWhenAll( new[] {server1, server2, server3 }, (tasks) => { // Propogate exceptions (see below) Task.WaitAll(tasks); return this.CompareTaskResults( tasks[0].Result, tasks[1].Result, tasks[2].Result); }); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This is clean, simple, and elegant. The one complication is the Task.WaitAll(tasks); statement. Although the continuation will not complete until all three tasks (server1, server2, and server3) have completed, there is a potential snag. If the networkClass.GetResults method fails, and raises an exception, we want to make sure to handle it cleanly. By using Task.WaitAll, any exceptions raised within any of our original tasks will get wrapped into a single AggregateException by the WaitAll method, providing us a simplified means of handling the exceptions. If we wait on the continuation, we can trap this AggregateException, and handle it cleanly. Without this line, it’s possible that an exception could remain uncaught and unhandled by a task, which later might trigger a nasty UnobservedTaskException. This would happen any time two of our original tasks failed. Just as we can schedule a continuation to occur when an entire collection of tasks has completed, we can just as easily setup a continuation to run when any single task within a collection completes. If, for example, we didn’t need to compare the results of all three network locations, but only use one, we could still schedule three tasks. We could then have our completion logic work on the first task which completed, and ignore the others. This is done via TaskFactory.ContinueWhenAny: var server1 = Task.Factory.StartNew( () => networkClass.GetResults(firstServer) ); var server2 = Task.Factory.StartNew( () => networkClass.GetResults(secondServer) ); var server3 = Task.Factory.StartNew( () => networkClass.GetResults(thirdServer) ); var result = Task.Factory.ContinueWhenAny( new[] {server1, server2, server3 }, (firstTask) => { return this.ProcessTaskResult(firstTask.Result); }); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Here, instead of working with all three tasks, we’re just using the first task which finishes. This is very useful, as it allows us to easily work with results of multiple operations, and “throw away” the others. However, you must take care when using ContinueWhenAny to properly handle exceptions. At some point, you should always wait on each task (or use the Task.Result property) in order to propogate any exceptions raised from within the task. Failing to do so can lead to an UnobservedTaskException.

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