How to clear graphics on a transparent control in windows forms

Question

So, I am pretty unfamiliar with windows forms development.

I'm trying to create a "hey I'm busy doing stuff" component that just spins a shape around. I want this control to be transient and draw on top of any other controls. The class inherits directly from Control.

So I have this in the constructor:

SetStyle(ControlStyles.Opaque, true);

and this:

protected override CreateParams CreateParams
{
    get
    {
        CreateParams parms = base.CreateParams;
        parms.ExStyle |= 0x20; 
        return parms;
    }
}

Which gets me a control that will draw on top of other controls.

Now my problem is this. I repaint the control a few times a second to give the appearane of a smooth animation. However, I can't figure out how to clear what was drawn in the previous frame. Using e.Graphics.Clear(Color.Transparent) in OnPaint turns the whole control black.

Is there a way to just clear the drawn contents of a control?

I've noticed that Resizing the the control will clear the background.

Things that Don't Work

1. Overriding OnPaintBackground to do nothing. Or just calling base.OnPaintBackground. Same results.

Answer 1

Okay, I found the solution here: http://www.bobpowell.net/transcontrols.htm

The Parent controls actually must be invalidated in order to retain the transparent background.

Answer 2

You may have to override OnPaintBackground that this article presents: http://saftsack.fs.uni-bayreuth.de/~dun3/archives/creating-a-transparent-panel-in-net/108.html

You may also need to Invalidate the control when it needs to be cleared to force OnPaintBackground to be called.