Hooking into Windows message loop in WPF window adds white border on the inside

Question

I am trying to create a WPF window with WindowStyle=\"None\" (for custom buttons and no title) that cannot be resized. Setting ResizeMode to

Answer 1

When you add your hook, you should only handle the messages you need to, and ignore the others. I believe you are handling certain messages twice, since you call DefWindowProc, but never set the handled parameter to true.

So in your case, you'd use:

private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled) {

    if (msg == (uint)WM.NCHITTEST) {
        handled = true;
        var htLocation = DefWindowProc(hwnd, msg, wParam, lParam).ToInt32();
        switch (htLocation) {
            case (int)HitTestResult.HTBOTTOM:
            case (int)HitTestResult.HTBOTTOMLEFT:
            case (int)HitTestResult.HTBOTTOMRIGHT:
            case (int)HitTestResult.HTLEFT:
            case (int)HitTestResult.HTRIGHT:
            case (int)HitTestResult.HTTOP:
            case (int)HitTestResult.HTTOPLEFT:
            case (int)HitTestResult.HTTOPRIGHT:
                htLocation = (int)HitTestResult.HTBORDER;
                break;
        }
        return new IntPtr(htLocation);
    }

    return IntPtr.Zero;
}

Also, I'd probably add the hook in an OnSourceInitialized override, like so:

protected override void OnSourceInitialized(EventArgs e) {
    base.OnSourceInitialized(e);

    IntPtr mainWindowPtr = new WindowInteropHelper(this).Handle;
    HwndSource mainWindowSrc = HwndSource.FromHwnd(mainWindowPtr);
    mainWindowSrc.AddHook(WndProc);
}