没有使用TransparencyKey触发MouseMove事件

Question

I'm creating a simple application that draws a horizontal and a vertical line following the mouse.

The form is transparent using TransparencyKey, and the lines are drawn using the Paint event:

private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Pen pen = new Pen(Color.Lime);
            e.Graphics.DrawLine(pen, 0, py, this.Size.Width, py);
            e.Graphics.DrawLine(pen, px, 0, px, this.Size.Height);
        }

private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            px = e.X; // get cursor X pos
            py = e.Y; // get cursor Y pos
            Invalidate(); // fire Paint event
        }

But the MouseMove event only is fired when the mouse is over the lines drawn. How to make the form catch mouse events when transparent? (Only the mouse move, I want the form still click-through)

Answer 1

As you can read here: http://msdn.microsoft.com/en-us/library/system.windows.forms.form.transparencykey%28v=vs.110%29.aspx - "Any mouse actions, such as the click of the mouse, that are performed on the transparent areas of the form will be transferred to the windows below the transparent area". One way to accomplish your goal is to write your own method, that will check the cursor relative position to the form in a loop, here's what I mean (it worked for me with TransparencyKey, resizing and moving the form):

private void MouseMovedWithTransparency()
{
   Point lastCursorPos = new Point(-1, -1); // Starting point.
   while (this.Visible)
   {
        Point currentCursorPos = Cursor.Position;
        if (this.ContainsFocus && currentCursorPos.X > this.Left && currentCursorPos.X < this.Left + this.Width &&
            currentCursorPos.Y > this.Top && currentCursorPos.Y < this.Top + this.Height)
        {
            if ((currentCursorPos.X != lastCursorPos.X) || (currentCursorPos.Y != lastCursorPos.Y))
            {
                // Do actions as in MouseMoved event.

                // Save the new position, so it won't be triggered, when user doesn't move the cursor.
                lastCursorPos = currentCursorPos;
            }
        }

        Application.DoEvents(); // UI must be kept responsive.
        Thread.Sleep(1);
    }
}

All you have to do now is to invoke this method from the Shown event - this.Visible has to be true, so it's the easiest way to make it work.