WinForm not receiving messages except right after creation

Question

I've got some unmanaged code sitting in a DLL. It publishes some methods that my calling (managed) code uses to hook into some COM notifications. Rather than deal with unmanaged code calling back into managed code, I've created a hidden Control derived object and am passing its handle property which the unmanaged code then uses as a parameter to SendMessage.

My Control derived class:

class InteropWindow : Control
{
  //delegate 
  private Handler m_callback;
  //window message
  private uint m_message;

  public InteropWindow(Handler callback, uint message)
    : base() 
  {
    m_callback = callback;
    m_message = message;
  }

  protected override void WndProc(ref Message m)
  {
    if (m.Msg == m_message)
    {
      m_callback(new IntPtr((int)m.WParam));
    }

    base.WndProc(ref m);
  }
}

Relevant line in unmanaged code:

SendMessage(m_notify, m_window_message, (WPARAM)pData, 0);

m_window_message & m_message are the same (both from RegisterWindowMessage), and m_notify == InteropWindow.Handle (pData varies, but is used as an opaque handle in the managed code). The unmanaged code is being invoked. These facts have been confirmed via debugging.

Shortly after I create the InteropWindow, the calls to SendMessage succeed. Afterwards (seconds later) the messages stop getting to WndProc, though there is no indication of any error.

The question is, what am I doing wrong here?

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I've ruled out lifecycle issues (to the best of knowledge anyway), and played with HandleRef to no avail.

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Edit the second.

I've re-written this to use function calls instead, which while fraught with its own perils, works a bit more like I'd expect. I've come to suspect this is a COM threading issue, but that's just a gut feeling.

Answer 1

Did you try passing your managed window's handle as a HandleRef? C# can marshal a HandleRef as an IntPtr and vice versa, I've seen Microsoft use that trick quite a bit when decompiling some of their stuff.

You can also load up a .Net profiler and watch the GC. It would be nice to know if your app is breaking right after a collect.