The animation on window closing does not appear after SetWindowRgn - wpf

Question

I want to show a window with a custom region and a custom appearance. I hook a window proc and set the custom region on WM_SIZE message by SetWindowRgn function. Also i process a WM_NCCALCSIZE to remove standard window frame.
[SecuritySafeCritical]
protected virtual IntPtr HwndSourceHookHandler(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled) {
if(msg == WinApi.WM_NCCALCSIZE) {
handled = true;
return IntPtr.Zero;
}
if(msg == WinApi.WM_SIZE) {
if(region != IntPtr.Zero)
WinApi.DeleteObject(region);
int width = lParam.ToInt32() & 0xFFFF;
int height = lParam.ToInt32() >> 16;
region = WinApi.CreateRoundRectRgn(0, 0, width, height, 40, 40);
WinApi.SetWindowRgn(new WindowInteropHelper(this).Handle, region, true);
}
return IntPtr.Zero;
}
The window is appeared on my Windows 8.1 OS with a round corners as expected and without border and window buttons. But i notice that in this case window is closed immediately without performing the close animation. If i comment SetWindowRgn, all works fine. Anyone knows what i am doing wrong?

Answer 1

The animation is being performed in the Window. Therefore, you need to stop the Window from actually closing when the close Button is pressed and start the animation then instead. When the animation is complete, then you should close the Window. This can be achieved as follows:
Handle the Window.Closing and Window.Close events:
private void AnimationWindow_Closing(object sender, CancelEventArgs e)
{
if (!isCloseAnimationComplete)
{
e.Cancel = true;
CloseWindow();
}
}
private void AnimationWindow_Close(object sender, RoutedEventArgs e)
{
CloseWindow();
}
public void CloseWindow()
{
// Set up animation
animation.Completed += CloseAnimation_Completed;
// Start animation
}
private void CloseAnimation_Completed(object sender, EventArgs e)
{
isCloseAnimationComplete = true;
// Actually close Window here
Close();
}