Issue with NSWorkspace and NSNotificationCentre's block-based API in Snow Leopard

Question

I've been having some trouble with Snow Leopard's new block-based API for observing notifications from NSWorkspace's NSNotificationCenter.

If I register for notifications using the traditional selector-based method, then I am able to observe the desired notification. If I try using the new method that takes a block, then it doesn't work.

In the code block below, setting usingBlockNotifications to either YES or NO should produce the same result, i.e. "didReceiveNoticationTest: called" printed to the console when an app launches, but I don't get the message when it's set to YES.

Any suggestions on what I'm doing wrong?

-(void)awakeFromNib

{

 BOOL usingBlockNotifications = YES;

 _notifcationObserver = nil;
 NSNotificationCenter *nc = [[NSWorkspace sharedWorkspace] notificationCenter];

 if (usingBlockNotifications)
 { 
  _notifcationObserver = 
  [nc addObserverForName:NSWorkspaceDidLaunchApplicationNotification
      object:[NSWorkspace sharedWorkspace]
       queue:nil
     usingBlock:^(NSNotification *arg1) {
      [self didReceiveNoticationTest:arg1];
     }];
  [_notifcationObserver retain];
 } else {
  [nc addObserver:self
      selector:@selector(didReceiveNoticationTest:)
       name:NSWorkspaceDidLaunchApplicationNotification
     object:[NSWorkspace sharedWorkspace]];
 }

}

-(void)didReceiveNoticationTest:(NSNotification *)notification
{
 NSLog(@"didReceiveNoticationTest: called");
}

Answer 1

I daresay this is a bug.

The following code prints both notifications. If you remove the selector version, nothing is printed. If you remove the block version the selector version still prints.

-(void)didReceiveNoticationTest1:(NSNotification *)notification
{
    NSLog(@"1: didReceiveNoticationTest: called");
}
-(void)didReceiveNoticationTest2:(NSNotification *)notification
{
    NSLog(@"2: didReceiveNoticationTest: called");
}

-(void)awakeFromNib

{
    NSNotificationCenter *nc = [[NSWorkspace sharedWorkspace] notificationCenter];

    [nc addObserver:self
           selector:@selector(didReceiveNoticationTest1:)
               name:NSWorkspaceDidLaunchApplicationNotification
             object:[NSWorkspace sharedWorkspace]];

    [[nc addObserverForName:NSWorkspaceDidLaunchApplicationNotification
                     object:[NSWorkspace sharedWorkspace]
                      queue:nil
                 usingBlock:^(NSNotification* arg1)
                            {
                                [self didReceiveNoticationTest2:arg1];
                            }] retain]; // this will leak.
}

Answer 2

Re-read the documentation for that method, specifically the part:

Return Value

An object or conforming to the NSObject protocol.

You must retain the returned value as long as you want the registration to exist in the notification center.