Loading a WPF Window without showing it

Question

I create a global hot key to show a window by PInvoking RegisterHotKey(). But to do this I need that window\'s HWND, which doesn\'t exist until the

Answer 1

You can also change the window into a so called message-only window. As this window type does not support graphical elements it will never be shown. Basically it comes down to calling:

    SetParent(hwnd, (IntPtr)HWND_MESSAGE);

Either create a dedicated message window which will always be hidden, or use the real GUI window and change it back to a normal window when you want to display it. See the code below for a more complete example.

    [DllImport("user32.dll")]
    static extern IntPtr SetParent(IntPtr hwnd, IntPtr hwndNewParent);

    private const int HWND_MESSAGE = -3;

    private IntPtr hwnd;
    private IntPtr oldParent;

    protected override void OnSourceInitialized(EventArgs e)
    {
        base.OnSourceInitialized(e);
        HwndSource hwndSource = PresentationSource.FromVisual(this) as HwndSource;

        if (hwndSource != null)
        {
            hwnd = hwndSource.Handle;
            oldParent = SetParent(hwnd, (IntPtr)HWND_MESSAGE);
            Visibility = Visibility.Hidden;
        }
    }

    private void OpenWindowMenuItem_Click(object sender, RoutedEventArgs e)
    {
        SetParent(hwnd, oldParent);
        Show();
        Activate();
    }

For me the solution of setting the width, height to zero and style to none didn't work out, as it still showed a tiny window, with an annoying shadow of what seems to be the border around a 0x0 window (tested on Windows 7). Therefore I'm providing this alternative option.