iOS发送验证码倒计时应用

- (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 }