iOS实现短信验证码倒计时

//启动一个定时器
self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(operatePerSecond) userInfo:nil repeats:YES];
 
//实现定时器中的方法
- (void)operatePerSecond {
    if (time == 1) {
      [self.timer invalidate];
      time = 60;
      [self.codeButton setTitle:@"重新获取" forState:UIControlStateNORMal];
      self.codeButton.tintColor = [UIColor blackColor];
      self.codeButton.enabled = YES;
    }else {
      time --;
      [self.codeButton setTitle:[NSString stringWithFormat:@"%ds" ,time] forState:UIControlStateNormal];
    }
}

  //倒计时时间
  __block int timeout = 60;
  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_TIME_NOW, 1.0 * NSEC_PER_SEC, 0 * NSEC_PER_SEC);
  dispatch_source_set_event_handler(timer, ^{
    if(timeout == 1){
      //倒计时结束，关闭
      dispatch_source_cancel(timer);
      dispatch_async(dispatch_get_main_queue(), ^{
      timeout = 60;
      [self.codeButton setTitle:@"重新获取" forState:UIControlStateNormal];
      self.codeButton.tintColor = [UIColor blackColor];
      self.codeButton.enabled = YES;
      });
    }else{
      NSString *strTime = [NSString stringWithFormat:@"%ds",timeout];
      dispatch_async(dispatch_get_main_queue(), ^{
        [self.codeButton setTitle:strTime forState:UIControlStateNormal];
      });
      timeout--;
    }
  });
dispatch_resume(timer);