blog: MEF and MVC - Limitations and workarounds for partial trust environments

MEFandMVC-Limitations-1-error.txt

Attempt by method 'DynamicClass.lambda_method(System.Runtime.CompilerServices.Closure)' 
to access type 'System.ComponentModel.Composition.Hosting.ComposablePartCatalogCollection' failed.
   

MEFandMVC-Limitations-2-web.config

<trust level="High"/>

MEFandMVC-Limitations-3-global.asax.cs

var cat = new DirectoryCatalog(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "bin"));
var parts = cat.Parts.ToArray();

MEFandMVC-Limitations-4-mefcontrollerfactory.cs

public class MefControllerFactory : IControllerFactory
{
    public IController CreateController(RequestContext requestContext, string controllerName)
    {
        var catalog = new DirectoryCatalog(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "bin"));
        var requestContainer = new CompositionContainer(catalog);
        var controller = requestContainer.GetExportedValue(controllerName);
 
        if (controller == null){ throw new HttpException(404, "Not found");}
         
        return controller;
    }
}

MEFandMVC-Limitations-5-containermanager.cs

public static class ContainerManager
{
    private static CompositionContainer _container;
    public static CompositionContainer ApplicationContainer
    {
        get
        {
            if (_container == null)
            {
                var catalog = new DirectoryCatalog(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "bin"));
                _container = new CompositionContainer(catalog);
            }
            return _container;
        }
    }
}

MEFandMVC-Limitations-6-MefHttpApplication.cs

public class MefHttpApplication : HttpApplication
{
    public static ComposablePartCatalog RootCatalog { get; private set; }
    public static CompositionContainer ApplicationContainer { get; private set; }
    public static ComposablePartCatalog ControllerCatalog { get; private set; }
 
    protected virtual void Application_Start()
    {
        if (RootCatalog == null){ RootCatalog = CreateRootCatalog(); }
        if (ApplicationContainer == null)
        {
            ApplicationContainer = new CompositionContainer(RootCatalog, false);
        }
        if (ControllerCatalog == null)
        {
            var controllerTypes = Assembly.GetExecutingAssembly().GetTypes().Where(t => t.GetInterfaces().Any(i => i == typeof(IController)));
            ControllerCatalog = new TypeCatalog(controllerTypes);
        }
        ControllerBuilder.Current.SetControllerFactory(new MefControllerFactory());
    }
 
    protected virtual void Application_End()
    {
        if (ApplicationContainer != null){ApplicationContainer.Dispose();}
    }
 
    protected virtual ComposablePartCatalog CreateRootCatalog()
    {
        return new DirectoryCatalog(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "bin"));
    }
}

MEFandMVC-Limitations-7-MvcApplication.cs

public class MvcApplication : MefHttpApplication
{
    public static void RegisterRoutes(RouteCollection routes)
    {
       //normal route stuff
    }
 
    protected override void Application_Start()
    {
        base.Application_Start();
        AreaRegistration.RegisterAllAreas();
        RegisterRoutes(RouteTable.Routes);
    }
}

MEFandMVC-Limitations-8-MefControllerFactory.cs

public class MefControllerFactory : IControllerFactory
{
    public IController CreateController(RequestContext requestContext, string controllerName)
    {
        var requestContainer = GetRequestControllerContainer(requestContext.HttpContext.Items);
        var controller = requestContainer.GetExportedValue(controllerName);
 
        if (controller == null){throw new HttpException(404, "Not found");}
 
        return controller;
    }
 
    public void ReleaseController(IController controller){/*nothing to do*/}
 
    public static CompositionContainer GetRequestControllerContainer(IDictionary contextItemsCollection)
    {
        var app = (MefHttpApplication)HttpContext.Current.ApplicationInstance;
 
        if (contextItemsCollection == null) throw new ArgumentNullException("dictionary");
 
        var container = (CompositionContainer)contextItemsCollection["MefRequestControllerContainer"];
 
        if (container == null)
        {
            container = new CompositionContainer(MefHttpApplication.ControllerCatalog, false, MefHttpApplication.ApplicationContainer);
            contextItemsCollection["MefRequestControllerContainer"] = container;
        }
        return container;
    }
}