Hi!

I'm writing a custom control and have a problem when the controls needs to redraw itself. Specifically, it's when you drag, for example, another window over my application's form containing the control. The redrawing of the control doesn't happen or the redrawing is incomplete.

I already set the ControlStyles AllPaintingInWmPaint, DoubleBuffer, ResizeRedraw and UserPaint.

I'm overriding the OnPaintBackground to draw a series of lines, like the following

protected override void OnPaintBackground(PaintEventArgs e) {     base.OnPaintBackground(e);     DrawGrid(e.ClipRectangle, e.Graphics); }

The DrawGrid method calls DrawLine on the Graphics objects in a for-loop - and only draws horizontal lines as it's supposed to. But when I drag a window over it, the redrawing is bad. Shouldn't be anything complicated though. I also call Invalidate(true) in the last line of DrawGrid, to invalidate and repaint the control and its children.

Can you see what I'm doing wrong?

Regards,
Patrick

Ok, I found the solution. It seemed, that I mistakenly thought that I needed to switch on the ControlStyles mentioned in the first post. That, combined with calling invalidate all the time, was the source of my problem.

Thanks for your help guys!

Sorry you are right. The AllPaintingInWmPaint control styles causes the framework to skip the OnPaintBackground and just call OnPaint.

you should call your control Invalidate() method I think...

When I call invalidate after having drawn the grid in the OnPaintBackground, the CPU usage goes to ~100%. This can't be the solution.

You are putting the invalidation in an infinite loop. If you are calling DrawGrid from the PaintBackground event, there is no need to call Invalidate from DrawGrid as the control is already Invalidating:

Your code path looks like the following:

1.) OnPaintBackground
2.) DrawGrid
3.) DrawGrid calls Invalidate which raises OnPaintBackground
4.) OnPaintBackground
5.) DrawGrid
6.) DrawGrid calls Invalidate which raises OnPaintBackground

and so on....

Remove the Invalidate() method from DrawGrid and see how it works. This is the best I can offer you without seeing any code.

You are drawing the grid only on the ClipRectangle. This rectangle represents the portion of the control that needs to be redrawn and does not represent the true size of the grid.

Try replace e.ClipRectangle with ClientRectangle.

Ok, I found the solution. It seemed, that I mistakenly thought that I needed to switch on the ControlStyles mentioned in the first post. That, combined with calling invalidate all the time, was the source of my problem.

Thanks for your help guys!

Well, as far as it looks now, the repainting is done appropriately. I'm not setting any control styles at all now, and it works when I drag a window over it. It updates automatically - I guess because of the invalidation that happens when dragging the window over.

What is the difference between painting in OnPaintBackground and OnPaint? Does it have anything to do with that, since I'm not painting anything (yet) in OnPaint?

Sorry you are right. The AllPaintingInWmPaint control styles causes the framework to skip the OnPaintBackground and just call OnPaint.

I believe calling Invalidate without any parameters causes ClipRectangle to equal ClientRectangle.

However you can't guarantee that as moving a window over a small portion of a the control will cause the ClipRectangle to equal the portion that was covered.

No, that is true, however I was referring to when he is calling Invalidate explicitly. Sorry for not being more clear in what I was saying.