Find which MDI child just got focus Win32 API

I have a program that has a MDI host and I would like to be able to get which of it children just got focus, bassiclly I would like to make a window focus changed event for this application.

The application is a 3rd party and I 开发者_如何学Pythondon't have the source, I have the window handle to the main program and the MDI host part.

I know I'll have to use Win32 API just not sure which ones.

I am writing my application in C#

Thanks.

I guess what you're looking for is intercepting WM_SETFOCUS and WM_KILLFOCUS messages

The real problem is how are you going to do this. I guess the easiet way is to install a hook which is a subroutine to monitor the message traffic in the system and process certain types of messages before they reach the target window procedure. You're doing it by using SetWindowsHookEx winapi function with WH_CALLWNDPROC or WH_CALLWNDPROCRET types of hooks. There some are examples posted on codeproject; also there is one on msdn: How to set a Windows hook in Visual C# .NET

What is not really clear in your post is where your code running: in the same process with the MDI windows or is it a separate application\service? In case it is you would also need to inject your code into the remote process. Check this link for details on how you can do it: Three Ways to Inject Your Code into Another Process

hope this helps, regards