[英]404 on Controllers in External Assemblies

I am having trouble resolving 404 responses in my Asp.Net MVC 4 project. It's built in VS2012 targeting 4.5.


I have pre-compiled views and controllers built into stand-alone DLLs. I am able to dynamically load the DLLs and inspect them from my core project, even invoke methods on them; however, it seems that the MVC Framework is not aware of the controllers. I am close here, but there is something missing.


Background on the Controllers and Views


Controllers are built in a stand-alone MVC project and inherit from Controller. Nothing too interesting going on there. The views use RazorGenerator and become classes that live in the project.


The output of the project is a DLL which correctly contains the controllers and views.


The DLLs implement a specific interface, we'll call it IPlugin, in a separate class (not part of a controller) in the library.


Loading the DLLs


Running as admin in Visual Studio I compile my app, which is hosted under IIS. With the project built, I drop a plugin DLL into my "Plugins" directory. Without debugging (this becomes important later), I open IE and navigate to the site. Note that at this point the App has been built, but never run, so startup events will fire. Everything here is still consistent if I recycle the app pool.

在Visual Studio中以管理員的身份運行我的應用程序,它托管在IIS下。項目完成后,我將一個插件DLL放到我的“插件”目錄中。無需調試(這在以后會變得很重要),我打開IE並導航到站點。注意,此時應用程序已經構建,但從未運行,因此啟動事件將啟動。如果我回收應用程序池,這里的一切都是一致的。

I have a Startup class with two methods, PreStart and PostStart and invoke the methods using WebActivator.PreApplicationStartMethod and WebActivator.PostApplicationStartMethod respectively.

我有一個包含兩個方法的Startup類,即PreStart和PostStart,並使用WebActivator調用這些方法。PreApplicationStartMethod WebActivator。PostApplicationStartMethod分別。

PreStart is where I do the following:


  • Get a list of all the plugin DLLs in my "Plugins" directory
  • 獲取我的“插件”目錄中所有插件dll的列表
  • Copy all plugins to AppDomain.CurrentDomain.DynamicDirectory
  • 將所有插件復制到AppDomain.CurrentDomain.DynamicDirectory
  • Load the type...if it contains an IPlugin I then
    • Add the assembly to the BuildManager
    • 將程序集添加到BuildManager
    • Call some of the methods on the class that implements IPlugin
    • 調用實現IPlugin類上的一些方法
  • 負載的類型……如果它包含一個IPlugin,那么我將程序集添加到BuildManager調用實現IPlugin的類上的一些方法

In 'PostStart' I do this bit of code (based on code from RazorGenerator.Mvc):


foreach (var assembly in Modules.Select(m=>m.Value))
    var engine = new PrecompiledMvcEngine(assembly)
        UsePhysicalViewsIfNewer = HttpContext.Current.Request.IsLocal

    ViewEngines.Engines.Insert(0, engine);

Modules in this context is a key/value pair where the values are the loaded assemblies. The purpose of this code is to make sure that MVC is aware of the views by adding a view engine for each assembly that knows how to resolve the views (this is part of RazorGenerator).


How I Know I'm Close (but Clearly Lacking the Cigar)


IPlugin defines a method called RegisterRoutes where, you guessed it, routes are to be registered for those who implement the interface. I call this method in PreStart and routes are added - I have verified that these exist in my route table. For instance, on a route defined in my plugin, created through dynamic invocation of the method during the PreStart, I see something like this as a DataToken when examining my routes:


Namespaces = Plugin.Name.Controllers

So, the route is registered, the assembly is loaded, I have verified that the DLL is correctly copied to the DynamicDirectory of the AppDomain. I am able to invoke members of classes that are loaded dynamically at runtime. But when I navigate to the URL that is matched by the route I get a 404. This is not a "could not locate view" YSOD, it's more akin to not finding the controller at all.


Here is the part that confuses the heck out of me: if, at this point, without doing anything, I return to Visual Studio and hit F5...everything works.

下面是讓我迷惑不解的部分:如果,此時,我什么也不做,回到Visual Studio,點擊F5……一切工作。

It's like Visual Studio is becoming aware of the controller in some way that I can't identify, and the MVC Framework is picking up on it.

就好像Visual Studio正在以某種我無法識別的方式意識到控制器,而MVC框架正在利用它。

Finally, A Question


What am I missing, and how do I get the MVC Framework to be aware of my controller?


And hey, at this point, if you're still reading this, thanks. :)


3 个解决方案



Turns out that this is a bug in Asp.Net itself.


After discussing the issue with Eilon Lipton of the Asp.Net team, and thinking this was something amiss in the MVC Framework, Eilon and a couple team members dug into things and found that the error was at a lower level per this conversation: http://aspnetwebstack.codeplex.com/discussions/403529

在與Asp的Eilon Lipton討論這個問題之后。Eilon和幾個團隊成員深入研究后發現,在這個對話中錯誤的級別更低:http://aspnetwebstack.codeplex.com/discussions/403529

They also suggested a workaround that included another call on BuildManager after the call to AddReferencedAssembly, which I implemented via the following code:


    // Add the plugin as a reference to the application

This allows you to add additional controllers/compiled views at startup in your pre-application init stage. What I'm doing now is looping through the list of DLLs in my plugins directory and pushing them to BuildManager as above.


The only limitation here is that you can't remove assemblies or clear the cache dynamically. The only way that I've found to do this is to add a previously unknown assembly to the referenced assemblies and compilation dependencies. I am experimenting with dynamically emitting a new assembly during pre-application initialization so that I can always, effectively, clear the cache and remove previously included plugins by faking a new assembly.


Hope this helps someone else out there.






It looks like this issue:


MVC uses assembly-qualified type name of the view engine to disambiguate view cache entries from different view engines. So it's not possible to have more than one PrecompiledMvcEngine object (as when you have precompiled views in more than one assembly). The problem can be solved by creating a different derived class from PrecompiledMvcEngine for each assembly. Or by creating a single generic derived class parameterized with some type from the assembly.


Article is here.




@MisterJames, take a look at this:


Asp.Net Mvc Pluggable Application

Asp。Net Mvc可插入應用程序

I hope it's useful.




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