- (IBAction)sendMes:(UIButton *)sender 
{ 
 __block int timeout = 10 ; //倒计时时间 
 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); //每秒执行 
 dispatch_source_set_event_handler(_timer, ^{ //每秒钟回调的方法 跟NSTimer 一样的的执行方法 
  if(timeout<=0){ //倒计时结束，关闭 
   dispatch_source_cancel(_timer); 
    
   dispatch_async(dispatch_get_main_queue(), ^{ 
    //设置界面的按钮显示 
    [sender setTitle:@"发送验证码" forState:UIControlStateNormal]; 
    sender.enabled = YES; 
   }); 
    
  }else{ 
   int seconds = timeout % 60; 
   NSString *strTime = [NSString stringWithFormat:@"%d", seconds]; 
   dispatch_async(dispatch_get_main_queue(), ^{ 
    NSLog(@"----%@", [NSThread currentThread]); 
    //设置界面的按钮显示 
    [sender setTitle:[NSString stringWithFormat:@"(%@)重新获取",strTime] forState:UIControlStateDisabled]; 
    sender.enabled = NO; 
   }); 
   timeout--; 
  } 
 }); 
 //一定要调用resume 开启定时器的功能 
}