如何在if语句中检查NSNotification

Question

I'm trying to run the following code, unless a NSNotification is sent. I can't figure out how to put the NSNotification in the if statement:

if (!self.subViewControllerProv) {
    self.subViewControllerProv = [[ProvViewController alloc] init];
}


[[NSNotificationCenter defaultCenter] addObserver:self
    selector:@selector(handleNotification:) name:@"SomeNotification" object:nil];

to recap: if the NSNotification message is observed then alloc and init the ProvViewController if not then don't.

Answer 1

Try adding an instance variable holding a flag for whether the notification has fired or not, set the flag in -handleNotification:, and then check for if when appropriate.

- (void)handleNotification:(NSNotification*)notification {
    _notificationWasPosted = YES;
}

...

if (!_notificationWasPosted && !self.subViewControllerProv) {
    self.subViewControllerProv = [[ProvViewController alloc] init];
}

Answer 2

Well what about doing something like this:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleNotification) name:@"SomeNotification" object:nil];

and then

-(void) handleNotification {
    //BOOL _hasBeenSent in your interface
    _hasBeenSent = YES;
}

And then in your code

if(_hasBeenSent) {
    NSLog(@"The notification has been sent!");
}