Is it possible to monitor other application using Cocoa on Mac? - objective-c

Question

For example, get the notification that another Application is becoming Active on the screen, or resign active state.

Answer 1

Sure. In your app delegate class, you can use NSWorkspace to get notified when an app becomes active (NSWorkspaceDidActivateApplicationNotification) or resigns active (NSWorkspaceDidDeactivateApplicationNotification). See the documentation on NSWorkspace for more info.
In your controller class, you'd do something like this:
- (id)init {
if ((self = [super init])) {
[[[NSWorkspace sharedWorkspace] notificationCenter] addObserver:self
selector:#selector(appDidActivate:)
name:NSWorkspaceDidActivateApplicationNotification
object:nil];
}
return self;
}
- (void)dealloc {
[[[NSWorkspace sharedWorkspace] notificationCenter] removeObserver:self];
[super dealloc];
}
- (void)appDidActivate:(NSNotification *)notification {
NSDictionary *userInfo = [notification userInfo];
NSLog(#"userInfo == %#", userInfo);
}
The key points are basically that you need to register to receive the notifications like shown in -init. You'd repeat the code to add another observer for each additional notification name that you want (e.g NSWorkspaceDidDeactivateApplicationNotification).
Another important thing to remember is to remove yourself as an observer in -dealloc (or elsewhere), so that NSWorkspace doesn't try to notify your controller object after it's been released+dealloc'd (and would no longer be valid).
In the specified -appDidActivate: method, do whatever you need to with the info about the app in question.

Answer 2

If you want something simpler than distributed objects, you could use distributed notifications from the distributed notification center. However, these are not posted unless you built the application. For monitoring when applications start or quit, you can use NSWorkspace and its notification center (suggested by NSGod)