Method not called with dispatch_async and repeating NSTimer

Question

I am developing an application in which I want to call a method in a separate queue using dispatch_async . I want to call this method again after a certain period of time. But the method is not called.

I do not know what happened. Here is my code:

 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

If you want a repeating timer to be called on dispatch_queue_t , use dispatch_source_create with 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); 

This creates a timer that starts once every 20 seconds (the third parameter is dispatch_source_set_timer ) with a delay of one second (the fourth parameter is before dispatch_source_set_timer ).

To cancel this timer, use dispatch_source_cancel :

 dispatch_source_cancel(timer); 

Answer 2

Try this code

  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 ); }); } 

Answer 3

 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); }); 

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