ASP.NET MVC 4 can be installed side by side with ASP.NET MVC 3 on the same computer, which gives you flexibility in choosing when to upgrade an ASP.NET MVC 3 application to ASP.NET MVC 4.
The simplest way to upgrade is to create a new ASP.NET MVC 4 project and copy all the views, controllers, code, and content files from the existing MVC 3 project to the new project and then to update the assembly references in the new project to match the old project. If you have made changes to the Web.config file in the MVC 3 project, you must also merge those changes into the Web.config file in the MVC 4 project.
To manually upgrade an existing ASP.NET MVC 3 application to version 4, do the following:

In all Web.config files in the project (there is one in the root of the project, one in the Views folder, and one in the Views folder for each area in your project), replace every instance of the following text:

  
System.Web.Mvc, Version=3.0.0.0 
System.Web.WebPages, Version=1.0.0.0 
System.Web.Helpers, Version=1.0.0.0 
System.Web.WebPages.Razor, Version=1.0.0.0

  
System.Web.Mvc, Version=4.0.0.0 
System.Web.WebPages, Version=2.0.0.0 
System.Web.Helpers, Version=2.0.0.0, 
 System.Web.WebPages.Razor, Version=2.0.0.0,

In the root Web.config file, update the webPages:Version element to "2.0.0.0" and add a new PreserveLoginUrl key that has the value "true":

<appSettings> 
  <add key="webpages:Version" value="2.0.0.0" /> 
  <add key="PreserveLoginUrl" value="true" /> 
<appSettings>

In Solution Explorer, delete the reference to System.Web.Mvc (which points to the version 3 DLL). Then add a reference to System.Web.Mvc (v4.0.0.0). In particular, make the following changes to update the assembly references. Here are the details:
1. In Solution Explorer, delete the references to the following assemblies:
  - System.Web.Mvc (v3.0.0.0)
  - System.Web.WebPages (v1.0.0.0)
  - System.Web.Razor (v1.0.0.0)
  - System.Web.WebPages.Deployment (v1.0.0.0)
  - System.Web.WebPages.Razor (v1.0.0.0)
2. Add a references to the following assemblies:
  - System.Web.Mvc (v4.0.0.0)
  - System.Web.WebPages (v2.0.0.0)
  - System.Web.Razor (v2.0.0.0)
  - System.Web.WebPages.Deployment (v2.0.0.0)
  - System.Web.WebPages.Razor (v2.0.0.0)
In Solution Explorer, right-click the project name and then select Unload Project. Then right-click the name again and select Edit ProjectName.csproj.
Locate the ProjectTypeGuids element and replace {E53F8FEA-EAE0-44A6-8774-FFD645390401} with {E3E379DF-F4C6-4180-9B81-6769533ABE47}.
Save the changes, close the project (.csproj) file you were editing, right-click the project, and then select Reload Project.

If the project references any third-party libraries that are compiled using previous versions of ASP.NET MVC, open the root Web.config file and add the following three bindingRedirect elements under the configuration section:

<configuration> 
  <!--... elements deleted for clarity ...--> 
  
  <runtime> 
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1"> 
      <dependentAssembly> 
        <assemblyIdentity name="System.Web.Helpers"  
             publicKeyToken="31bf3856ad364e35" /> 
        <bindingRedirect oldVersion="1.0.0.0" newVersion="2.0.0.0"/> 
      </dependentAssembly> 
      <dependentAssembly> 
        <assemblyIdentity name="System.Web.Mvc"  
             publicKeyToken="31bf3856ad364e35" /> 
        <bindingRedirect oldVersion="1.0.0.0-3.0.0.0" newVersion="4.0.0.0"/> 
      </dependentAssembly> 
      <dependentAssembly> 
        <assemblyIdentity name="System.Web.WebPages"  
             publicKeyToken="31bf3856ad364e35" /> 
        <bindingRedirect oldVersion="1.0.0.0" newVersion="2.0.0.0"/> 
      </dependentAssembly> 
    </assemblyBinding> 
  </runtime> 
</configuration>

New Features in ASP.NET MVC 4 Developer Preview

This section describes features that have been introduced in the ASP.NET MVC 4 Developer Preview release.

Enhancements to Default Project Templates

The template that is used to create new ASP.NET MVC 4 projects has been updated to create a more modern-looking website:

In addition to cosmetic improvements, there’s improved functionality in the new template. The template employs a technique called adaptive rendering to look good in both desktop browsers and mobile browsers without any customization.

To see adaptive rendering in action, you can use a mobile emulator or just try resizing the desktop browser window to be smaller. When the browser window gets small enough, the layout of the page will change.
Another enhancement to the default project template is the use of JavaScript to provide a richer UI. The Login and Register links that are used in the template are examples of how to use the jQuery UI Dialog to present a rich login screen:

Mobile Project Template

If you’re starting a new project and want to create a site specifically for mobile and tablet browsers, you can use the new Mobile Application project template. This is based on jQuery Mobile, an open-source library for building touch-optimized UI:

This template contains the same application structure as the Internet Application template (and the controller code is virtually identical), but it's styled using jQuery Mobile to look good and behave well on touch-based mobile devices. To learn more about how to structure and style mobile UI, see the jQuery Mobile project website.
If you already have a desktop-oriented site that you want to add mobile-optimized views to, or if you want to create a single site that serves differently styled views to desktop and mobile browsers, you can use the new Display Modes feature. (See the next section.)

Display Modes

The new Display Modes feature lets an application select views depending on the browser that's making the request. For example, if a desktop browser requests the Home page, the application might use the Views\Home\Index.cshtml template. If a mobile browser requests the Home page, the application might return the Views\Home\Index.mobile.cshtml template.
Layouts and partials can also be overridden for particular browser types. For example:

If your Views\Shared folder contains both the _Layout.cshtml and _Layout.mobile.cshtml templates, by default the application will use _Layout.mobile.cshtml during requests from mobile browsers and _Layout.cshtml during other requests.

If a folder contains both _MyPartial.cshtml and _MyPartial.mobile.cshtml, the instruction @Html.Partial("_MyPartial") will render _MyPartial.mobile.cshtml during requests from mobile browsers, and _MyPartial.cshtml during other requests.

If you want to create more specific views, layouts, or partial views for other devices, you can register a new DefaultDisplayMode instance to specify which name to search for when a request satisfies particular conditions. For example, you could add the following code to the Application_Start method in the Global.asax file to register the string "iPhone" as a display mode that applies when the Apple iPhone browser makes a request:

DisplayModes.Modes.Insert(0, new DefaultDisplayMode("iPhone") 
{ 
    ContextCondition = (context => context.Request.UserAgent.IndexOf 
        ("iPhone", StringComparison.OrdinalIgnoreCase) >= 0) 
 });

After this code runs, when an Apple iPhone browser makes a request, your application will use the Views\Shared\_Layout.iPhone.cshtml layout (if it exists).

jQuery Mobile, the View Switcher, and Browser Overriding

jQuery Mobile is an open source library for building touch-optimized web UI. If you want to use jQuery Mobile with an ASP.NET MVC 4 application, you can download and install a NuGet package that helps you get started. To install it from the Visual Studio Package Manager Console, type the following command:

Install-Package jQuery.Mobile.MVC

This installs jQuery Mobile and some helper files, including the following:

Views/Shared/_Layout.Mobile.cshtml, which is a jQuery Mobile-based layout.

A view-switcher component, which consists of the Views/Shared/_ViewSwitcher.cshtml partial view and the ViewSwitcherController.cs controller.

After you install the package, run your application using a mobile browser (or equivalent, like the Firefox User Agent Switcher add-on). You'll see that your pages look quite different, because jQuery Mobile handles layout and styling. To take advantage of this, you can do the following:

Create mobile-specific view overrides as described under Display Modes earlier (for example, create Views\Home\Index.mobile.cshtml to override Views\Home\Index.cshtml for mobile browsers).

Read the jQuery Mobile documentation to learn more about how to add touch-optimized UI elements in mobile views.

A convention for mobile-optimized web pages is to add a link whose text is something like Desktop view or Full site mode that lets users switch to a desktop version of the page. The jQuery.Mobile.MVC package includes a sample view-switcher component for this purpose. It's used in the default Views\Shared\_Layout.Mobile.cshtml view, and it looks like this when the page is rendered:

If visitors click the link, they’re switched to the desktop version of the same page.
Because your desktop layout will not include a view switcher by default, visitors won't have a way to get to mobile mode. To enable this, add the following reference to _ViewSwitcher to your desktop layout, just inside the <body> element:

<body> 
    @Html.Partial("_ViewSwitcher") 
    ...

The view switcher uses a new feature called Browser Overriding. This feature lets your application treat requests as if they were coming from a different browser (user agent) than the one they're actually from. The following table lists the methods that Browser Overriding provides.

`HttpContext.SetOverriddenBrowser(userAgentString)`	Overrides the request's actual user agent value using the specified user agent.
`HttpContext.GetOverriddenUserAgent()`	Returns the request's user agent override value, or the actual user agent string if no override has been specified.
`HttpContext.GetOverriddenBrowser()`	Returns an HttpBrowserCapabilitiesBase instance that corresponds to the user agent currently set for the request (actual or overridden). You can use this value to get properties such as IsMobileDevice.
`HttpContext.ClearOverriddenBrowser()`	Removes any overridden user agent for the current request.

Browser Overriding is a core feature of ASP.NET MVC 4 and is available even if you don't install the jQuery.Mobile.MVC package. However, it affects only view, layout, and partial-view selection — it does not affect any other ASP.NET feature that depends on the Request.Browser object.
By default, the user-agent override is stored using a cookie. If you want to store the override elsewhere (for example, in a database), you can replace the default provider (BrowserOverrideStores.Current). Documentation for this provider will be available to accompany a later release of ASP.NET MVC.

Recipes for Code Generation in Visual Studio

The new Recipes feature enables Visual Studio to generate solution-specific code based on packages that you can install using NuGet. The Recipes framework makes it easy for developers to write code-generation plugins, which you can also use to replace the built-in code generators for Add Area, Add Controller, and Add View. Because recipes are deployed as NuGet packages, they can easily be checked into source control and shared with all developers on the project automatically. They are also available on a per-solution basis.

Task Support for Asynchronous Controllers

You can now write asynchronous action methods as single methods that return an object of type Task or Task<ActionResult>.
For example, if you're using Visual C# 5 (or using the Async CTP), you can create an asynchronous action method that looks like the following:

public async Task<ActionResult> Index(string city) { 
    var newsService = new NewsService(); 
    var sportsService = new SportsService(); 
     
    return View("Common", 
        new PortalViewModel { 
        NewsHeadlines = await newsService.GetHeadlinesAsync(), 
        SportsScores = await sportsService.GetScoresAsync() 
    }); 
}

In the previous action method, the calls to newsService.GetHeadlinesAsync and sportsService.GetScoresAsync are called asynchronously and do not block a thread from the thread pool.
Asynchronous action methods that return Task instances can also support timeouts. To make your action method cancellable, add a parameter of type CancellationToken to the action method signature. The following example shows an asynchronous action method that has a timeout of 2500 milliseconds and that displays a TimedOut view to the client if a timeout occurs.

[AsyncTimeout(2500)] 
 [HandleError(ExceptionType = typeof(TaskCanceledException), View = "TimedOut")] 
public async Task<ActionResult> Index(string city, 
    CancellationToken cancellationToken) { 
    var newsService = new NewsService(); 
    var sportsService = new SportsService(); 
    
    return View("Common", 
        new PortalViewModel { 
        NewsHeadlines = await newsService.GetHeadlinesAsync(cancellationToken), 
        SportsScores = await sportsService.GetScoresAsync(cancellationToken) 
    }); 
}

Azure SDK

ASP.NET MVC 4 Developer Preview supports the September 2011 1.5 release of the Windows Azure SDK.

Known Issues and Breaking Changes

The "Add Controller" item template in Visual Basic projects generates an incorrect namespace when invoked from inside an area. When you add a controller to an area in an ASP.NET MVC project that uses Visual Basic, the item template inserts the wrong namespace into the controller. The result is a "file not found" error when you navigate to any action in the controller.
The generated namespace omits everything after the root namespace. For example, the namespace generated is RootNamespace but should be RootNamespace.Areas.AreaName.Controllers.
There are issues when running ASP.NET MVC 3, ASP.NET MVC 4, and Windows Azure Tools for Visual Studio 2010 1.5 side by side. Windows Azure Tools for Visual Studio 2010 1.5 provides ASP.NET MVC 3 and ASP.NET MVC 4 web roles. Installing ASP.NET MVC 4 on a computer that already has ASP.NET MVC 3 installed causes the Azure deployment packages that contain an ASP.NET MVC 3 web role to fail to run after deployment. The workaround is to right-click the project, select Add Deployable Assemblies, and then choose ASP.NET MVC.
Creating an ASP.NET MVC 4 project with unit tests that targets the .NET Framework 4.5 results in a unit test project that won’t compile. The workaround is to change the unit test project to target the .NET Framework 4.5. To retarget the project, right-click the project in Solution Explorer and then select Properties. Make sure the Application tab is selected and then change the Target Framework to .NET Framework 4.5.
There is a compatibility issue when using scaffolding with the .NET Framework 4.5 Developer Preview installed on Windows 8 Developer Preview. The .NET Framework 4.5 Developer Preview on Windows 8 introduces a breaking change into the Visual Basic compiler that affects the Add Controller dialog box for ASP.NET MVC 3 in Visual Studio 2010. If you use the Entity Framework controller scaffolder in an ASP.NET MVC 3 project that uses Visual Basic, you'll see the error message "There is not enough information to call IEnumerable.GetEnumerator on Windows Runtime object …"
Breaking changes in the Razor View Engine. As part of a rewrite of the Razor parser, the following types were removed from System.Web.Mvc.Razor:
- ModelSpan
- MvcVBRazorCodeGenerator
- MvcCSharpRazorCodeGenerator
- MvcVBRazorCodeParser
The following methods were also removed:
- MvcCSharpRazorCodeParser.ParseInheritsStatement(System.Web.Razor.Parser.CodeBlockInfo)
- MvcWebPageRazorHost.DecorateCodeGenerator(System.Web.Razor.Generator.RazorCodeGenerator)
- MvcVBRazorCodeParser.ParseInheritsStatement(System.Web.Razor.Parser.CodeBlockInfo)
When WebMatrix.WebData.dll is included in in the /bin directory of an ASP.NET MVC 4 apps, it takes over the URL for forms authentication. Adding the WebMatrix.WebData.dll assembly to your application (for example, by selecting "ASP.NET Web Pages with Razor Syntax" when using the Add Deployable Dependencies dialog) will override the authentication login redirect to /account/logon rather than /account/login as expected by the default ASP.NET MVC Account Controller. To prevent this behavior and use the URL specified already in the authentication section of web.config, you can add an appSetting called PreserveLoginUrl and set it to true:
```
<appSettings> 
    <add key="PreserveLoginUrl" value="true"/> 
</appSettings>
```
Installing ASP.NET MVC 4 Developer Preview breaks ASP.NET MVC 3 RTM applications. ASP.NET MVC 3 applications that were created with the RTM release (not with the ASP.NET MVC 3 Tools Update release) require the following changes in order to work side-by-side with ASP.NET MVC 4 Developer Preview. Building the project without making these updates results in compilation errors. Required updates
1. In the root Web.config file, add a new <appSettings> entry with the key webPages:Version and the value 1.0.0.0.
2. In Solution Explorer, right-click the project name and then select Unload Project. Then right-click the name again and select Edit ProjectName.csproj.
3. Locate the following assembly references:
```
<Reference Include="System.Web.WebPages"/>  
<Reference Include="System.Web.Helpers" />
```
  Replace them with the following:
```
<Reference Include="System.Web.WebPages, Version=1.0.0.0, 
Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL "/>  
<Reference Include="System.Web.Helpers, Version=1.0.0.0, 
Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL" />
```
4. Save the changes, close the project (.csproj) file you were editing, and then right-click the project and select Reload.
Mobile Project Template support for VB.NET. There is currently no mobile project template for Visual Basic. Changes for Visual Basic project templates will be available in a future release.
View without @model declaration results in a compiler error. A Razor view that does not declare the model type using the @model declaration and that accesses server side code using the @ syntax results in a compiler error. This is a regression from the behavior of ASP.NET MVC 3. As a workaround, use the @model declaration. If you don’t want to specify a type, use @model dynamic.

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Wednesday 19 October 2011

Upgrading an ASP.NET MVC 3 Project to ASP.NET MVC 4