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Global hotkeys in Cocoa on Snow Leopard

So I got this new MacBook Pro with Snow Leopard. One granny said that carbon won’t be supported on 64 bit platforms on Snow Leopard. So I was really interested how do I implement global hotkeys on 64 bit platform without using carbon.

NSEvent class addGlobalMonitorForEventsMatchingMask:handler: method provides this functionality. General declaration for this method looks like this:

+ (id)addGlobalMonitorForEventsMatchingMask:(NSEventMask)mask handler:(void (^)(NSEvent*))block

Since we’re monitoring the global event, block passed to method as event handler returns void (i.e. it can’t modify passed in event). But we can do anything we please inside the block. Most common usage pattern would be to activate an app and show it’s key window. It’s possible implement it in two ways: via window controller object or notifications.

Here how it’d look using window controller object (assuming MainWindowController is created before adding event monitor):

// AppDelegate.m
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
  ...
  [NSEvent addGlobalMonitorForEventsMatchingMask:NSKeyDownMask 
                                         handler:^{
    [NSApp activateIgnoringOtherApps:YES];
    [mainWindowController showWindow:self];
  }];
  ...
}

In example above – any key down while your app is inactive will activate your app and show window mainWindowController is responsible for.

The second one IMHO is cleaner and has wider application: using NSNotification. It requires code in application controller and application delegate. Both code pieces are independent.

// AppDelegate.m
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
  [NSEvent addGlobalMonitorForEventsMatchingMask:NSKeyDownMask 
                                         handler:^{
    ...
    int flags = [event modifierFlags];
    int altDown = flags & NSOptionKeyMask;
    if (([event keyCode] == 7) && altDown) {
      [[NSNotificationCenter defaultCenter] postNotificationName:@"OpenMainWindow" object:nil];
    };
    ...
  }];
};
 
// AppController.m
- (void)awakeFromNib {
  // Let's register for "OpenMainWindow" notification in AppController.
  NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
  [nc addObserver:self 
         selector:@selector(showMainWindow:) 
             name:@"OpenMainWindow"
           object:nil];
}
 
- (void)showMainWindow:(id)sender {
  // Open main window. Simple.
  [mainWindowController showWindow:sender];
}

UPDATE: as Antonio stated in the comments you need enable access for assistive devices via System Preferences app.

Reference: addGlobalMonitorForEventsMatchingMask:handler: @ Mac Dev Center