Windows Forms FAQ resources

11. Windows Forms Mouse Handling

11.8 Why am I not receiving MouseLeave messages in a Control in my Form?

This usually happens when a Control doesn't know that the mouse has left its bounds following a mouse enter. This results in the Control not throwing a MouseLeave event for subsequent mouse moves over it.

This is possible if you performed some operation when the mouse was within a Control that made it lose its mouse capture, for example, opening a top-level window over the Control such that the mouse is now over this new window.

To work around this problem send a WM_MOUSELEAVE manually to the original Control before the offending operation.

class NativeMethods

{

[DllImport("user32.dll", CharSet=CharSet.Auto)]

extern public static IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wParam, IntPtr lParam) ;

}

// Send a WM_MOUSELEAVE manually to a window.

NativeMethods.SendMessage(control.Handle, NativeMethods.WM_MOUSELEAVE, IntPtr.Zero, IntPtr.Zero);