protected override void WndProc(ref Message m)
{
switch (m.Msg)
{
case PI.WM_MOUSEACTIVATE:
// Prevent the popup window becoming active just because the user has
// pressed the mouse over the window, so return NOACTIVATE as result.
m.Result = (IntPtr)PI.MA_NOACTIVATE;
return;
}
base.WndProc(ref m);
}