/**

 *  倒计时GCD通用方法

 *  通常用的计时器都是用NSTimer，但是NSTimer在线程很吃紧的时候效果不佳，使用GCD计时相对更好

 *

 *  @param seconds   倒计时间 单位：秒

 *  @param showLable 需要显示的文本框

 *  @param endBlock  倒计时结束后，回调的Block

 */

- (void)startTimerWithSeconds:(long)seconds showLable:(UILabel *)showLable endBlock:(void (^)())endBlock

{

    __block long timeout = seconds; // 倒计时时间

    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, );

    dispatch_source_t _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, , ,queue);

    dispatch_source_set_timer(_timer,dispatch_walltime(NULL, ),1.0 * NSEC_PER_SEC, ); //每秒执行

    dispatch_source_set_event_handler(_timer, ^{

        if(timeout < ){ // 倒计时结束，回调block

            dispatch_source_cancel(_timer);

            dispatch_async(dispatch_get_main_queue(), ^{

                if (endBlock) {

                    endBlock();

                }

            });

        } else{

            NSString *strTime = [NSString stringWithFormat:@"%02ld分%02ld秒",(long)(timeout %  / ), (long)(timeout  % )];

            // 回到主界面,显示倒计时

            dispatch_async(dispatch_get_main_queue(), ^{

                showLable.text = strTime;

            });

            timeout--;

        }

    });

    dispatch_resume(_timer);

}

[self startTimerWithSeconds: showLable:self.timerLabel endBlock:nil];