ios GCD中的倒计时与延时函数

///倒计时
    __block NSInteger time = 7; //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, ^{
        if(time <= 0){ //倒计时结束，关闭
            dispatch_source_cancel(_timer);
            dispatch_async(dispatch_get_main_queue(), ^{
                //设置按钮的样式
                NSLog(@"延迟到七秒才出来");
            });
        } else {
            NSInteger seconds = time % 60;
            dispatch_async(dispatch_get_main_queue(), ^{
                //设置按钮显示读秒效果
                NSLog(@"倒计时---(%.2ld)秒",(long)seconds);
            });
            time--;
        }
    });
    dispatch_resume(_timer);
   
///延时执行
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(8 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        NSLog(@"延迟到八秒才出来");
    });