Why does the SendMessage() function not work?

Question

I try to send a WM_LBUTTONDOWN and WM_LBUTTONUP messages to a window( simulating mouse clicks without moving the cursor ).

My program is working very good on many windows, but there are a few that don't work :( Like Registry Editor, Yahoo Messenger, some Firefox sites, etc...

How can I make to work with those from above ??

NOTE#1: I use Win7

NOTE#2: My code is just calling the api and functions and aply them on the specific window handle. Its working ok but not on all windows :(

Answer 1

It is another aspect of UAC, called UIPI or User Interface Privacy Isolation that could cause this trouble. Designed to prevent a program that run un-elevated from hijacking the capabilities of an elevated one. That certainly explains the trouble with Regedit.exe, clearly UAC would be ineffective if a program could commandeer it to poke stuff into the registry. You'd have to run your program elevated to bypass this restriction.

Another one is that SendMessage() doesn't properly simulate mouse input. The messages you are sending are normally posted to the message queue. You need to use PostMessage() instead. You should also emulate WM_MOUSEMOVE.

The proper way to simulate mouse input is through SendInput(). That one exactly emulates the mouse driver behavior, there's no way for a program to tell the difference. But with the added requirement that you have to make sure that whatever program you are trying to automate runs in the foreground. That's very difficult, SetForegroundWindow() isn't reliable enough. So only consider SendInput() if you actually only want to send mouse messages to the foreground window, whatever it might be.