Call C# dll library methods from Silverlight 5 via PInvoke

Question

I know I cannot add reference to c# dll library in Silverlight application if it's not Silverlight library. But I've a question - can I treat this dll like unmanaged code and use PInvoke like with C/C++ libraries ? I had try with sample project dll library:

namespace TestLib
{
    public class TestClass
    {
        public static int Add(int x, int y)
        {
            return x + y;
        }
    }
}

And in my silverlight application:

[System.Runtime.InteropServices.DllImport("TestLib.dll", EntryPoint = "TestLib.Add", CallingConvention = System.Runtime.InteropServices.CallingConvention.StdCall)]
        public static extern int Add(int x, int y);

but I'm getting an error while trying to invoke method:

Unable to find an entry point named 'TestLib.Add' in DLL

and if I try without namespace:

Unable to find an entry point named 'Add' in DLL

Can You point me with some hits ? Note, I've also tried to compile this dll as Silverlight application but there are some methods unsupported by Silverlight.

Answer 1

I think this MSDN Article is relevant to your problem. It seems to be possible, but your DLL isn't in C#, is it ? Because if it is then a PInvoke might not works.

Answer 2

I'd use COM for interop with your C# dll rather than trying Pinvoke. Expose some classes in you dll as COM objects, then use JavaScript to create those COM objects, and call their functions.

  var progid = "TestLib.MyObject";
  var TestLibObject = new ActiveXObject(progid);
  var result = TestLibObject.Add(1, 2);

Once I had the JavaScript calls working with the COM object I wrapped them in a class to represent the COM object in Silverlight.

public class MyObject
{
  string varName = "myObject";
  public MyObject()
  {
    string js = "var " + varName + " = new ActiveXObject(\"TestLib.MyObject\");"
    HtmlPage.Window.Eval(js);
  }
  public int Add(int x, int y)
  {
    string js = string.Format("{0}.Add({1},{3});", varName, x, y);
    return (int)HtmlPage.Window.Eval(js);
  }
}

You may want to refer to http://msdn.microsoft.com/en-us/library/cc645031(v=vs.95).aspx to see how manages types are passed to/from JavaScript.

If you still want to use Pinvoke you could try UnmanagedExports . It adds a DllExport attribute that you can use to expose a function to native code. You should then be able to Pinvoke this function.

In my own project I had success with using COM/JavaScript for interop in Silverlight. I haven't tried UnmanagedExports/Pinvoke in Silverlight.