design-time writer’s block

I discovered, much to my surprise, that Blend 2 has the necessary infrastructure to support rudimentary custom extensions.  The extensions take the form of a class which implements the public interface Microsoft.Expression.Framework.AddIn.IAddIn.

Inline is a very simple HelloWorld sample.

AddInDescription("HelloWorld", AddInCategory.Tool)]
public class HelloWorld : IAddIn
{
    public void Initialize(IApplicationService 
      applicationService) {}

    public void StartupComplete()
    {
        // Show we were here
        System.Windows.MessageBox.Show("Hi");
    }

    public void ShuttingDown() {}

    IDisposable Members
}

AddIns are hooked on startup, specified as command line arguments:
path\to\blend.exe /addin:HelloWorld.dll

When initialized, an Application ServiceProvider object reference is passed, which contains accessors to all the major service provider objects of Blend.  Through this, it’s possible to add custom menus and dialogs, possibly even panels, to Blend.

I expect there are alot of limitations.  The most glaring is loading Addins only by specifying them as commandline arguments. Much of Blend is internal and/or sealed, including Nautilus (Blend’s code editor), Visual Studio abstractions for Projects, Solutions, and the Build system.  Enough remains open to allow for some customization of existing features, and certainly for new features.

More discovery needs to be done.