Alternatives to NativeWindow for subclassing

Question

I am subclassing a Win32 window in managed code using NativeWindow. However, I'm encountering a bug in either my code or with NativeWindow that throws an exception when the parent is closed. The code I'm using is this:

public partial class ThisAddIn

{

private VisioWindow visioWindow;

private void ThisAddIn_Startup(object sender, System.EventArgs e)

{

    visioWindow = new VisioWindow();

    visioWindow.AssignHandle(new IntPtr(this.Application.Window.WindowHandle32));

}

private void ThisAddIn_Shutdown(object sender, System.EventArgs e)

{

    visioWindow.ReleaseHandle();

}

#region VSTO generated code

/// <summary>

/// Required method for Designer support - do not modify

/// the contents of this method with the code editor.

/// </summary>

private void InternalStartup()

{

    this.Startup += new System.EventHandler(ThisAddIn_Startup);

    this.Shutdown += new System.EventHandler(ThisAddIn_Shutdown);

}

#endregion

public class VisioWindow : NativeWindow

{

    protected override void WndProc(ref Message m)

    {

        base.WndProc(ref m);

    }

}

}

On exit of the main program, I get this error:

A first chance exception of type 'System.Threading.ThreadAbortException' occurred in System.Windows.Forms.dll A first chance exception of type 'System.Threading.ThreadAbortException' occurred in System.Windows.Forms.dll

And the "This program has encountered an error" shows up saying the parent encountered an error.

Is there a different way to override the parent's WndProc than using NativeWindow? Or is there a bug in this code that could be worked out?

Thanks.

Answer 1

It isn't exactly clear to me why it would crash. Use Debug + Exception, Thrown flag to find out where the ThreadAbort exception is coming from. One thing is definitely wrong, you should detach the handle when the window is destroyed. You could do this by watching for the WM_NCDESTROY message:

protected override void WndProc(ref Message m) {
  base.WndProc(ref m);
  if (m.Msg == 0x82) this.ReleaseHandle();
}