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¿Enviar y recibir mensajes a través de NSNotificationCenter en Objective-C?

Question

Estoy intentando enviar y recibir mensajes a través de NSNotificationCenter en Objective-C. Sin embargo, no he podido encontrar ningún ejemplo sobre cómo hacer esto. ¿Cómo se envían y reciben mensajes a través de NSNotificationCenter ?

Answer 1

Este me ayudó

// Add an observer that will respond to loginComplete
[[NSNotificationCenter defaultCenter] addObserver:self 
                                             selector:@selector(showMainMenu:) 
                                                 name:@"loginComplete" object:nil];


// Post a notification to loginComplete
[[NSNotificationCenter defaultCenter] postNotificationName:@"loginComplete" object:nil];


// the function specified in the same class where we defined the addObserver
- (void)showMainMenu:(NSNotification *)note {
    NSLog(@"Received Notification - Someone seems to have logged in"); 
}

Fuente: http://www.smipple.net/snippet/Sounden/Simple%20NSNotificationCenter%20example

Answer 2

Para ampliar el ejemplo de Dreamlax ... Si desea enviar datos junto con la notificación

En el código de publicación:

NSDictionary *userInfo = 
[NSDictionary dictionaryWithObject:myObject forKey:@"someKey"];
[[NSNotificationCenter defaultCenter] postNotificationName: 
                       @"TestNotification" object:nil userInfo:userInfo];

En el código de observación:

- (void) receiveTestNotification:(NSNotification *) notification {

    NSDictionary *userInfo = notification.userInfo;
    MyObject *myObject = [userInfo objectForKey:@"someKey"];
}

Answer 3

Si está utilizando NSNotificationCenter para actualizar su vista, no olvide enviarlo desde el hilo principal llamando a dispatch_async :

dispatch_async(dispatch_get_main_queue(),^{
    [[NSNotificationCenter defaultCenter] postNotificationName:@"my_notification" object:nil];
});

Answer 4

También existe la posibilidad de utilizar bloques:

NSOperationQueue *mainQueue = [NSOperationQueue mainQueue];
[[NSNotificationCenter defaultCenter] 
     addObserverForName:@"notificationName" 
     object:nil
     queue:mainQueue
     usingBlock:^(NSNotification *notification)
     {
          NSLog(@"Notification received!");
          NSDictionary *userInfo = notification.userInfo;

          // ...
     }];

La documentación de apple

Answer 5

@implementation TestClass

- (void) dealloc
{
    // If you don''t remove yourself as an observer, the Notification Center
    // will continue to try and send notification objects to the deallocated
    // object.
    [[NSNotificationCenter defaultCenter] removeObserver:self];
    [super dealloc];
}

- (id) init
{
    self = [super init];
    if (!self) return nil;

    // Add this instance of TestClass as an observer of the TestNotification.
    // We tell the notification center to inform us of "TestNotification"
    // notifications using the receiveTestNotification: selector. By
    // specifying object:nil, we tell the notification center that we are not
    // interested in who posted the notification. If you provided an actual
    // object rather than nil, the notification center will only notify you
    // when the notification was posted by that particular object.

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

    return self;
}

- (void) receiveTestNotification:(NSNotification *) notification
{
    // [notification name] should always be @"TestNotification"
    // unless you use this method for observation of other notifications
    // as well.

    if ([[notification name] isEqualToString:@"TestNotification"])
        NSLog (@"Successfully received the test notification!");
}

@end

... en otro lugar en otra clase ...

- (void) someMethod
{

    // All instances of TestClass will be notified
    [[NSNotificationCenter defaultCenter] 
        postNotificationName:@"TestNotification" 
        object:self];

}