Question

Basically the problem is that I’d like to invoke a method in an unreferenced assembly, but can’t seem to find the right call for instantiating the class. I’ve tried things like a simple Type t = Type.GetType("MyApp.Helper") which returns null, and Assembly.LoadFrom("MyApp.Helper") which throws a security exception.

In the example below, two projects/assemblies (Helper.dll and Menu.dll) are compiled separately into a common ‘libs’ folder, but do not reference each other. Main.dll references both, and the references are set to ‘Copy local’ in VS. So when the app runs, the Main.xap should contain all three assemblies and they should be loaded into the same application domain. Or so goes my understanding. Is this an impossible quest? I see lots of comments regarding plug-ins but so far I haven’t seen examples for this specific design. For example, I suppose I could do something like Jeff Prosise describes here, but I’d rather have everything in one package.

Here’s a sketch of my code:

In one project/assembly, I have a worker class:

namespace MyApp.Helper {  
    public class Helper {  
        public void ShowHelp() {  
            Console.Write("Help!");  
        }  
    }  
}  

In another project/assembly, I have a menu class which tries to invoke the helper:

namespace MyApp.Menu {
    public class Selector {
        public void InvokeSelection(string className, string functionName) {

            // fails: t will be null
            Type t = Type.GetType(className);  

            // fails: t will be null
            t = Type.GetType(string.Format("{0}.{1}, {0}, Version=1.0.0.0, Culture=\"\", PublicTokenKey=null", "MyApp.Helper", "Helper"));

            // however, this works (reference to main assembly?)
            t = Type.GetType(string.Format("{0}.{1}, {0}, Version=1.0.0.0, Culture=\"\", PublicTokenKey=null", "MyApp.Main", "Worker"));

            // and, I'd like to do something like the following
            // t.InvokeMember(functionName, ...);
        }
    }
}

Finally, I have the main app assembly:

namespace MyApp.Main {
    public class Main {
        public static void Main() {
            MyApp.Menu.Selector sel = new Menu.Selector();
            sel.InvokeSelection("MyApp.Help.Helper", "ShowHelp");  // fails
            sel.InvokeSelection("MyApp.Main.Main", "Worker"); // works in some cases
        }
        public void Worker() {
            Console.Write("Work!");
        }
    }
}

Thanks for any ideas!

-Chris.

Answer 1

You need to get the Assembly object, then call its GetType method.

However, I don’t see why you’re using Reflection at all.
You can call the method normally from your main project.