How can I find out if there are windows above a control?

If I have a Winforms control, is it possible to tell if ther开发者_如何转开发e are windows (from any application) above it? Basically, I need to know what parts of my control are actually visible on screen.

If you're happy to P/Invoke, the EnumWindows function enumerates all top-level windows on the screen giving a HWND; from that you can get the non-client rectangle (GetWindowRect) to compare against your form bounds.

This won't account for windows with non-rectangular opaque areas (fancy skins for media players and the like), so you may get false positives for such a window occluding your control.

In the Win32 API, you can use WindowFromPoint to determine the topmost window at any given point. This won't tell you if your whole control is visible, but if you test all 4 corners it gives you pretty good odds.

Why do you want this information? Typically when people ask this question it's because they want to ensure that their UI is in the foreground if it's not. And that usually is what happens just before they try to steal the focus away from the application which does have the foreground.

And foreground stealing is very, very, very bad. People get REALLY upset when applications steal focus.

Having said that, either of the two techniques above would work - I think I'd prefer the EnumWindows/GetWindowRect/IntersectRect technique in Steve Gilham's answer.