Windows/C++: detect when focus has changed between windows (globally)

Question

I'm trying to find a way to detect when focus is changed to another window (without having to poll every X ms).

I've already figured out a way to detect when focus is switched between applications using WH_SHELL and HSHELL_ACTIVATESHELLWINDOW.

The problem is I want to detect when focus is switched between dialog/windows within the same app.

ie. In Notepad, I can determine when the app switches to Notepad, but I cannot detect when the "Open" or "Save" dialogs appear because the focus is still within the same application.

Answer 1

You can use SetWindowsHookEx with a WH_CBT hook type. If you just want to detect focus changes within an application, pass GetCurrentThreadId() as the last parameter, otherwise the hook will be for all threads on the current desktop.

Note that using windows hooks can have an adverse effect on system performance, so the hook should only be installed when necessary and you should do a minimum amount of work in the hook procedure.

Answer 2

How about the "Computer Based Training API"; SetWindowsHookEx with WH_CBT which will enable you to receive HCBT_SETFOCUS (among others)