Question

I have a control (derived from System.Windows.Forms.Control) which needs to be transparent in some areas. I have implemented this by using SetStyle():

public TransparentControl() {     SetStyle(ControlStyles.SupportsTransparentBackColor, true);     this.BackColor = Color.Transparent. } 

Now, this works if there are no controls between the form and the transparent control. However, if there happens to be another control below the transparent control (which is the use case here), it does not work. The intermediate control is not draw, but the form below does show through. I can get the effect that I need by overriding CreateParams and setting the WS_EX_TRANSPARENT flasg like so:

protected override CreateParams CreateParams {     get     {         CreateParams cp = base.CreateParams;         cp.ExStyle |= 0x20; // WS_EX_TRANSPARENT         return cp;     } } 

The problem here is that it really slows down the painting of the control. The control is already double buffered, so nothing to do there. The performance hit is so bad that it is unacceptable. Has anyone else encountered this problem? All of the resources that I can find suggest using method #1, but again, that does not work in my case.

EDIT: I should note that I do have a workaround. The child (transparent) controls could simply draw themselves onto the parent’s Graphics object, but it is really ungly and I don’t like the solution at all (though it may be all I have).

EDIT2: So, following the advice that I got on how transparency works in .NET, I have implemented the IContainer interface in my user control which contains the transparent controls. I have created a class which implements ISite, I add my child controls to the Components collection of the UserControl, the Container property lines up correctly in the debugger, but I still do not get a transparency effect. Does anyone have any ideas?

Answer 1

I decided to simply paint the parent under my child controls manually. Here is a good article.