iOS -计数器的实现 计数精度秒

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-(UILabel *)timeLable{
    if(!_timeLable){
        _timeLable=[[UILabel alloc]init];
        __block NSInteger second = 0;
        __block NSInteger min = 0;
        __block NSInteger hour = 0;
        //全局队列    默认优先级
        dispatch_queue_t quene = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
        //定时器模式  事件源
        dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, quene);
        //_timer = timer;
        //NSEC_PER_SEC是秒，＊1是每秒
        dispatch_source_set_timer(timer, dispatch_walltime(NULL, 0), NSEC_PER_SEC * 1, 0);
        //设置响应dispatch源事件的block，在dispatch源指定的队列上运行
        dispatch_source_set_event_handler(timer, ^{
            //回调主线程，在主线程中操作UI
            dispatch_async(dispatch_get_main_queue(), ^{
                if (second >= 0) {
                    if(second == 60){
                        second =0;
                        min++;
                        if (min == 60) {
                            min =0;
                            hour++;
                        }
                    }
                    _timeLable.text = [NSString stringWithFormat:@"正在看房中:%.2ld:%.2ld:%.2ld",hour,min,second];
                    second++;
                }
                else
                {
                    //这句话必须写否则会出问题
                    dispatch_source_cancel(timer);
                    _timeLable.text = @"正在看房中*****";
                }
            });
        });
        //启动源
        dispatch_resume(timer);
        if (@available(iOS 8.2, *)) {
            _timeLable.font = [UIFont systemFontOfSize:18 weight:0.2];
        }
        [_timeLable setTextColor:[UIColor redColor]];
    }
    return _timeLable;
}