metodo non chiamato con dispatch_async e ripetendo NSTimer

Question

Sto sviluppando un'applicazione in cui voglio chiamare il metodo in coda separata usando dispatch_async. Voglio chiamare quel metodo ripetutamente dopo un certo intervallo di tempo. Ma il metodo non viene chiamato.

Non so cosa c'è di sbagliato. Ecco il mio codice:

dispatch_async(NotificationQueue, ^{ 

     NSLog(@"inside queue"); 
     timer = [NSTimer scheduledTimerWithTimeInterval: 20.0 
               target: self 
               selector: @selector(gettingNotification) 
               userInfo: nil 
               repeats: YES]; 

     dispatch_async(dispatch_get_main_queue(), ^{ 
      // Add code here to update the UI/send notifications based on the 
      // results of the background processing 

     }); 
    }); 

-(void)gettingNotification { 
    NSLog(@"calling method "); 
} 

Answer 1

Se si desidera un timer ripetuto da richiamare su un dispatch_queue_t, utilizzare dispatch_source_create con un DISPATCH_SOURCE_TYPE_TIMER:

dispatch_queue_t queue = dispatch_queue_create("com.firm.app.timer", 0); 
dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue); 
dispatch_source_set_timer(timer, dispatch_walltime(NULL, 0), 20ull * NSEC_PER_SEC, 1ull * NSEC_PER_SEC); 

dispatch_source_set_event_handler(timer, ^{ 

    // stuff performed on background queue goes here 

    NSLog(@"done on custom background queue"); 

    // if you need to also do any UI updates, synchronize model updates, 
    // or the like, dispatch that back to the main queue: 

    dispatch_async(dispatch_get_main_queue(), ^{ 
     NSLog(@"done on main queue"); 
    }); 
}); 

dispatch_resume(timer); 

che crea un timer che viene eseguito una volta ogni 20 secondi (3 ° parametro dispatch_source_set_timer), con un margine di manovra di un un secondo (4 ° parametro dispatch_source_set_timer).

Per annullare questo timer, utilizzare dispatch_source_cancel:

dispatch_source_cancel(timer); 

Answer 2

int parameter1 = 12; 
float parameter2 = 144.1; 

// Delay execution of my block for 10 seconds. 
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 10 * NSEC_PER_SEC), dispatch_get_current_queue(), ^{ 
    NSLog(@"parameter1: %d parameter2: %f", parameter1, parameter2); 
}); 

sguardo per più

How do you trigger a block after a delay, like -performSelector:withObject:afterDelay:?

Answer 3

Prova questo codice

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ 

    dispatch_async(dispatch_get_main_queue(), ^{ 

     timer = [NSTimer scheduledTimerWithTimeInterval: 1.0 target: self 
               selector: @selector(gettingNotification) userInfo: nil repeats: YES]; 
     // Add code here to update the UI/send notifications based on the 
     // results of the background processing 

    }); 
}); 

-(void)gettingNotification { 

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ 
     //background task here 
    dispatch_async(dispatch_get_main_queue(), ^{ 
     // update UI here 
     ); 
}); 
}