get current focused window id using objective c

Question

hi developers, how can i get current focused window id using objective c, the return value should be an int, help is highly appreciated! I just need to get the following line working

CGImageRef windowImage = CGWindowListCreateImage(CGRectNull, kCGWindowListOptionIncludingWindow, winNum, kCGWindowImageBoundsIgnoreFraming);

but no matter which window that i focus at, winNum is always 0.

Answer 1

NSWindow *keyTarget = [[NSApplication sharedApplication] keyWindow];
NSInteger winNum = [keyTarget windowNumber];

or in one line:

[[[NSApplication sharedApplication] keyWindow] windowNumber];

Answer 2

i have tried it out, but no matter which window that i focus at, winNum is always 0, any idea or am i missing anything? I just need to get the following line working

CGImageRef windowImage = CGWindowListCreateImage(CGRectNull, kCGWindowListOptionIncludingWindow, winNum, kCGWindowImageBoundsIgnoreFraming);

*please note that i'm not trying to get the window id of my own application. it should be an application that i'm focusing at