Two Ways to Realize Countdown in ios

Method 1: Use NSTimer to implement

The scheduledTimerWithTimeInterval method of NSTimer is mainly used to execute the timeFireMethod function once every 1 second, and timeFireMethod carries out some operations of countdown. When it is completed, timer is given to invalidate and ok is dropped. The code is as follows:

 secondsCountDown = 60;//60 Seconds countdown  
 countDownTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(timeFireMethod) userInfo:nil repeats:YES]; 
-(void)timeFireMethod{ 
  secondsCountDown--; 
  if(secondsCountDown==0){ 
   [countDownTimer invalidate]; 
  } 
} 

Method 2: Use GCD to implement

The code is as follows:

__block int timeout=300; // Countdown time  
 dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); 
 dispatch_source_t _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,queue); 
 dispatch_source_set_timer(_timer,dispatch_walltime(NULL, 0),1.0*NSEC_PER_SEC, 0); // Execute per second  
 dispatch_source_set_event_handler(_timer, ^{ 
   if(timeout<=0){ // End of countdown, close  
     dispatch_source_cancel(_timer); 
     dispatch_release(_timer); 
     dispatch_async(dispatch_get_main_queue(), ^{ 
// Set the button display of the interface   Set according to your own needs  
        . . . . . . . .  
     }); 
   }else{ 
     int minutes = timeout / 60; 
     int seconds = timeout % 60; 
     NSString *strTime = [NSString stringWithFormat:@"%d Points %.2d Retrieve the verification code after seconds ",minutes, seconds]; 
     dispatch_async(dispatch_get_main_queue(), ^{ 
       // Set the button display of the interface   Set according to your own needs  
 . . . . . . . .  
     }); 
     timeout--; 
   } 
 }); 
 dispatch_resume(_timer); 

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