Finding the Startup Assembly at Design Time in WPF

Question

I have a WPF MarkupExtension that needs to access resources in the default resource assembly. Extension works fine at runtime, but fails in the designer as the extension can't find the default resources in the startup assembly. In order to load up a ResourceManager I need to know what assembly to load the resources from.

At runtime I can handle this easily by passing in an Assembly at Initialization - that works just fine.

However, at Design Time none of this startup code executes so the designer bombs and fails to load the page. So how can I get one of the following generically (without referencing specific application types):

• The Application's startup assembly (ie. the WPF EXE)
• The Current XAML Document the Markup Extension is hosted on

Answer 1

Assembly.GetEntryAssembly.FullName will give you #1. For your other problem, wouldn't Assembly.GetExecutingAssembly do it?

Answer 2

AFAIK, there's no easy and clean way to do that... I use the following method, which looks for an assembly that has an entry-point (i.e. an executable assembly) and contains a class derived from System.Windows.Application :

    public static Assembly GetEntryAssembly()
    {
        // Should work at runtime
        Assembly asm = Assembly.GetEntryAssembly();

        // Design time
        if (asm == null)
        {
            asm = (
                   from a in AppDomain.CurrentDomain.GetAssemblies()
                   where a.EntryPoint != null
                   && a.GetTypes().Any(t => t.IsSubclassOf(typeof(System.Windows.Application)))
                   select a
                  ).FirstOrDefault();
        }

        return asm;
    }

This code needs to be adjusted for specific needs (for instance, it won't work for a WPF control library)

If you prefer to retrieve the XAML root element, you could find some inspiration in the code of a markup extension I wrote some time ago. It finds the root element by using reflection on private/internal fields.

Answer 3

This is exactly what I'm looking for. However, I'm not using the WPF's System.Windows.Application.

Can you help me with the code if I'm trying to get the assembly of the Windows Application in design-time when the code is on a usercontrol that is on one of the forms in the Windows Application?

I've tried the code below, but it "asm" is null:

System.Reflection.Assembly asm = (from a in AppDomain.CurrentDomain.GetAssemblies() where a.EntryPoint != null && a.GetTypes().Any(t => t.IsSubclassOf(typeof(System.Windows.Forms.Application))) select a ).FirstOrDefault();