Question

I use MAF and I have a problem with activating the addin. Let me explain my plan.

First I create a secondary AppDomain then I try to activate the addin:

MyAddIn = Token.Activate<AddInHostView>(domain);

My AddIn is very simple and referenced only one helper assembly. If this helper assembly is in the directory of the AddIn, all things work like a charm.

AddIns

• MyDemoAddIn.dll
• Helpers.dll

If I delete the Helpers.dll the whole application crash:

A first chance exception of type ‘System.IO.FileNotFoundException’ occurred in MyDemoAddIn.DLL
‘PresentationHost.exe’ (Managed (v4.0.30319)): Loaded ‘C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\mscorlib.resources\v4.0_4.0.0.0_de_b77a5c561934e089\mscorlib.resources.dll’
A first chance exception of type ‘System.Reflection.TargetInvocationException’ occurred in mscorlib.dll
A first chance exception of type ‘System.Reflection.TargetInvocationException’ occurred in System.AddIn.dll
A first chance exception of type ‘System.Reflection.TargetInvocationException’ occurred in System.AddIn.dll

I tested all things with exception handling. I can’t catch the exception from the Host, AddInView or my created AppDomain 🙁

Does anyone have an idea?

Answer 1

The answer is easier than you think… The problem was a error in the Finalizer() Method from the AddInView.dll which is an interlayer of the MAF. Here is my solution.

Demo (Host)

try
{
    MyAddIn = Token.Activate<AddInHostView>(domain);
}
catch (Exception ex)
{
    try
    {
        AppDomain.Unload(domain);
        domain = null;
    }
    catch (ThreadAbortException threadAbortException)
    {
        //ToDo: Logging
    }
    catch (CannotUnloadAppDomainException cannotUnloadAppDomainException)
    {
        //ToDo: Logging
    }
    catch (Exception exception)
    {
        //ToDo: Logging
    }
}

AddInView

[AddInBase]
public class AddInView : UserControl
{
    //Necessary constructor to handle the exception.
    //Normal constructor is not called when an error occurs at startup!!!
    static AddInView()
    {
        AppDomain.CurrentDomain.DomainUnload += CurrentDomain_DomainUnload;
    }

    //Normal constructor
    public AddInView()
    {
        //Do other things...
        //e.g. Dispatcher.UnhandledException += Dispatcher_UnhandledException;
    }

    static void CurrentDomain_DomainUnload(object sender, EventArgs e)
    {
        //To cleanup and stuff
    }
}

Now, if an error occurs (Activate<>) the exception handler catches the error (FileNotFound Helpers.dll not found) and unload the whole AppDomain without crash the main AppDomain 🙂