WPF: How do I make a custom modal dialog flash?

Question

Normally when you open a Modal Dialog and try to click on it's parent window the Modal Dialog's titlebar flashes. When creating a custom, borderless, chromeless, window in WPF you lose all that functionality and must rebuild it yourself. I've looked high and low and for the life of me cannot figure out how to get my Modal window to flash. Though it still beeps...

I figure I'm going to have to watch for some event(s) in WndProc that I'll have to handle, but I can't figure out which event or how to do it. I've tried watching the window changed and window changing event as well as the WM_ACTIVATE event to no avail. I'm sure I'm just missing something simple, but I would appreciate any help on this. Thanks!

Answer 1

private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
    {
        var retVal = IntPtr.Zero;

        switch (msg)
        {
            case UnsafeNativeConstants.WM_NCACTIVATE:
                retVal = UnsafeNativeMethods.DefWindowProc(hwnd, UnsafeNativeConstants.WM_NCACTIVATE, new IntPtr(1), new IntPtr(-1));
                AssociatedObject.UpdateTitlebar((int)wParam == 1 ? true : false);
                handled = true;
                break;
        }

        return retVal;
    }

The WndProc I have hooked up in a custom behavior that's attached to my window. It calls an internal method on my window that will update the color of the Titlebar appropriately.

Thanks to @Hans Passant for pointing me in the right direction.