Using the WPF Dispatcher in unit tests

Question

I\'m having trouble getting the Dispatcher to run a delegate I\'m passing to it when unit testing. Everything works fine when I\'m running the program, but, during a unit te

Answer 1

We've solved this issue by simply mocking out the dispatcher behind an interface, and pulling in the interface from our IOC container. Here's the interface:

public interface IDispatcher
{
    void Dispatch( Delegate method, params object[] args );
}

Here's the concrete implementation registered in the IOC container for the real app

[Export(typeof(IDispatcher))]
public class ApplicationDispatcher : IDispatcher
{
    public void Dispatch( Delegate method, params object[] args )
    { UnderlyingDispatcher.BeginInvoke(method, args); }

    // -----

    Dispatcher UnderlyingDispatcher
    {
        get
        {
            if( App.Current == null )
                throw new InvalidOperationException("You must call this method from within a running WPF application!");

            if( App.Current.Dispatcher == null )
                throw new InvalidOperationException("You must call this method from within a running WPF application with an active dispatcher!");

            return App.Current.Dispatcher;
        }
    }
}

And here's a mock one that we supply to the code during unit tests:

public class MockDispatcher : IDispatcher
{
    public void Dispatch(Delegate method, params object[] args)
    { method.DynamicInvoke(args); }
}

We also have a variant of the MockDispatcher which executes delegates in a background thread, but it's not neccessary most of the time