Help: Ownerdraw TabControl

Question

Hi, nildo,
I want to create a MyTabControl based on TabControl. By rewriting OnPaint() I draw tabarea and tad head, all works but I can not make background transparent. The background is alway be filled by grey color. I can only fill it by other color but can not make it transparent. TabControl can make background transparent itself.

I tried the way as below.
SetStyle(ControlStyles.SupportsTransparentBackColor, true);
this.BackColor = Color.Transparent;
But it does not work. It looks like that the background is filled with grey by some code before my OnPaint() is called.

Thanks.
David.

Zoran Horvat · Answer

I have played with owner-drawn TabControl once and found it full of limitations. I think it does not support transparent background because it conveniently draws background for you, right before it gives you opportunity to draw in a Paint event. Even if you do something about this, borders will be drawn by the base class and you won't have opportunity to change that (I think). One work-around for transparency is to find all controls below tab control and then use their DrawToBitmap method to capture their image. Then combine those images to draw background. Note that you should use double-buffered tab control in that case to avoid flickering (inheirt tab control and set its DoubleBuffered property to true in the constructor). This workaround may become simple if you know what lays under the tab control, but general case seems difficult. That is one lesson in controls programming - do not help inheritors too much, don't try to read their minds. But most of the built-in Windows forms controls act against that guideline.