Asp.net-mvc – Session null in ASP.Net MVC Controller Constructors

asp.net-mvcsession

Why is Session null in the constructors of Controllers? It can be accessed from Action methods. Presumably, because the MVC Routing framework is responsible for newing-up a Controller, it just hasn't (re-)instantiated the Session at that point.

Does anyone know if this is by design and, if so, why?

[I have managed to circumvent the problem by using a Lazy Loading Pattern.]

Best Answer

Andrei is right - it is null because when running under the ASP.NET MVC framework, the HttpContext (and therefore HttpContext.Session) is not set when the controller class is contructed as you might expect, but it set ("injected") later by the ControllerBuilder class. If you want a better understanding of the lifecycle you can either pull down the ASP.NET MVC framework (the source is available), or refer to: this page

If you need to access the Session then one way would be to override the "OnActionExecuting" method and access it there, as it will be available by that time.

However, as Andrei is suggesting, if your code is reliant on the Session then it could potentially be difficult to write unit tests, so perhaps you could consider wrapping the Session in a helper class which can then be swapped out for a different, non-web version when running under unit tests, therefore de-coupling your controller from the web.

Related Solutions

Asp.net-mvc – Can an ASP.NET MVC controller return an Image

Use the base controllers File method.

public ActionResult Image(string id)
{
    var dir = Server.MapPath("/Images");
    var path = Path.Combine(dir, id + ".jpg"); //validate the path for security or use other means to generate the path.
    return base.File(path, "image/jpeg");
}

As a note, this seems to be fairly efficient. I did a test where I requested the image through the controller (http://localhost/MyController/Image/MyImage) and through the direct URL (http://localhost/Images/MyImage.jpg) and the results were:

MVC: 7.6 milliseconds per photo
Direct: 6.7 milliseconds per photo

Note: this is the average time of a request. The average was calculated by making thousands of requests on the local machine, so the totals should not include network latency or bandwidth issues.

Asp.net-mvc – Compile Views in ASP.NET MVC

From the readme word doc for RC1 (not indexed by google)

ASP.NET Compiler Post-Build Step

Currently, errors within a view file are not detected until run time. To let you detect these errors at compile time, ASP.NET MVC projects now include an MvcBuildViews property, which is disabled by default. To enable this property, open the project file and set the MvcBuildViews property to true, as shown in the following example:

<Project ToolsVersion="3.5" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <MvcBuildViews>true</MvcBuildViews>
  </PropertyGroup>

Note Enabling this feature adds some overhead to the build time.

You can update projects that were created with previous releases of MVC to include build-time validation of views by performing the following steps:

Open the project file in a text editor.
Add the following element under the top-most <PropertyGroup> element: <MvcBuildViews>true</MvcBuildViews>
At the end of the project file, uncomment the <Target Name="AfterBuild"> element and modify it to match the following:

<Target Name="AfterBuild" Condition="'$(MvcBuildViews)'=='true'">
    <AspNetCompiler VirtualPath="temp" PhysicalPath="$(ProjectDir)\..\$(ProjectName)" />
</Target>

Best Answer

Related Solutions

Asp.net-mvc – Can an ASP.NET MVC controller return an Image

Asp.net-mvc – Compile Views in ASP.NET MVC

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