In your application’s controller add the following:

   1  - (void)awakeFromNib
   2  {
   3  	[self registerHotKeys];
   4  }

And the following code which registers the hot keys:

   1  -(void)registerHotKeys
   2  {	
   3      EventHotKeyRef gMyHotKeyRef;
   4      EventHotKeyID gMyHotKeyID;
   5      EventTypeSpec eventType;
   6      eventType.eventClass=kEventClassKeyboard;
   7      eventType.eventKind=kEventHotKeyPressed;	
   8  	
   9      InstallApplicationEventHandler(&OnHotKeyEvent, 1, &eventType, (void *)self, NULL);
  10  	
  11      gMyHotKeyID.signature='htk1';
  12      gMyHotKeyID.id=1;
  13      RegisterEventHotKey(20, cmdKey+optionKey, gMyHotKeyID, GetApplicationEventTarget(), 0, &gMyHotKeyRef);	
  14  	
  15      gMyHotKeyID.signature='htk2';
  16      gMyHotKeyID.id=2;	
  17      RegisterEventHotKey(21, cmdKey+optionKey, gMyHotKeyID, GetApplicationEventTarget(), 0, &gMyHotKeyRef);	
  18  	
  19      gMyHotKeyID.signature='htk3';
  20      gMyHotKeyID.id=3;	
  21      RegisterEventHotKey(23, cmdKey+optionKey, gMyHotKeyID, GetApplicationEventTarget(), 0, &gMyHotKeyRef);	
  22  }
  23  
  24  OSStatus OnHotKeyEvent(EventHandlerCallRef nextHandler,EventRef theEvent,void *userData)
  25  {
  26      EventHotKeyID hkCom;
  27  	
  28      GetEventParameter(theEvent, kEventParamDirectObject, typeEventHotKeyID, NULL, sizeof(hkCom), NULL, &hkCom);
  29      AppController *controller = (AppController *)userData;	
  30  	
  31      int l = hkCom.id;
  32  	
  33      switch (l) {
  34          case 1: 		
  35  			NSLog(@"Capture area");	
  36  			[ScreenCapture captureArea:controller];
  37  			break;
  38          case 2: 
  39  			NSLog(@"Capture screen");	
  40  			[ScreenCapture captureScreen:controller];
  41  			break;
  42          case 3: 
  43  			NSLog(@"Capture window");	
  44  			[ScreenCapture captureWindow:controller];
  45  			break;  
  46      }
  47  
  48      return noErr;
  49  }

The code used in this snippet was inspired by this blog post http://dbachrach.com/blog/2005/11/28/program-global-hotkeys-in-cocoa-easily/

Alternatives

If you need a more complete solution you can use one of these open-source alternatives:

• NDHotKeyEvent
• HotKeysLib3

Showing the application window

Usually you want to show the application window when the hot key is pressed. This can be done as explained in this snippet