How do I get Mouse Messages on my Control during design-time?

The design-time will forward the MouseEnter and MouseLeave messages to your Control by default. The MouseMove message are blocked by the designer. You can get MouseDown and Up messages in your Control if you override GetHitTest method in your designer and return true, as follows:

protected override /*ControlDesigner*/ bool GetHitTest(Point point)
{
	if(this.NeedMouseDown(point))
		return true;
	else
		return false;
}