Why does GetExportedValues ​​<T> () no longer work after using the final .net 4 MEF release?

Over the past few months, I've been developing an extensible infrastructure management app using community preview. I am using the GetExportedValues ​​() method and PartCreationPolicy (CreationPolicy.NonShared) to spoof the factory class (since only the silverlight version supports factory). This works great until I updated the project to use .net 4.0. There is no error, it just doesn't work.

So why does this code stop working? The code follows:

Factory method:

public static IEnumerable<DataActionBase> GetActionsFromDirectory(string PluginsFolder)
{
    IEnumerable<DataActionBase> result = null;

    var catalog = new DirectoryCatalog(PluginsFolder);
    var container = new CompositionContainer(catalog: catalog);

    result = container.GetExportedValues<DataActionBase>();

    return result;
}

      

        
        
        
      

    

Example Export class:

[Export(typeof(DataActionBase))]
[PartCreationPolicy(CreationPolicy.NonShared)]
public class AnAction : DataActionBase
{
    ....
}