Question

When mouse is rapidly dragged out of the window with left button pressed Mouse.DirectlyOver returns System.Windows.Controls.Grid instead of null.

Window.IsMouseOver returns true

new Rect(window.RenderSize).Contains(Mouse.GetPosition(window)) returns true

To reproduce that, simply add checking timer to MainWindow() in a blank wpf project like that:

    public MainWindow()
    {
        InitializeComponent();
        var timer = new System.Threading.Timer(state =>
            Dispatcher.BeginInvoke(new Action(
                () => Debug.WriteLine("Mouse.DirectlyOver = {0}", Mouse.DirectlyOver)
                )),null,0,10);
    }

When i drag out slowly, the values are correct.

Is there a workaround for that? What is the coorect way to determine mouse is out of the application?

Answer 1

Found a workaround.
On every tick I retrieve the mouse position with WinAPI’s

 [DllImport("user32.dll")]
 [return: MarshalAs(UnmanagedType.Bool)]
 internal static extern bool GetCursorPos(ref Win32Point pt);

And then check in within borders of the window manually.