倒计时

一个方法搞定！上代码~

#define kCoolDownTime 60
+ (void)countDownStart:(UIButton *)btn {
    __block int timeout = kCoolDownTime; //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(timeout <= 0){
            //倒计时结束，关闭
            dispatch_source_cancel(_timer);
            dispatch_async(dispatch_get_main_queue(), ^{
                //UI更新
                btn.userInteractionEnabled = YES;
                btn.titleLabel.font = [UIFont systemFontOfSize:17];
                [btn setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
                [btn setBackgroundColor:[UIColor orangeColor]];
                [btn setTitle:@"获取验证码" forState:UIControlStateNormal];
            });
        }
        else {
            dispatch_async(dispatch_get_main_queue(), ^{
                btn.userInteractionEnabled = NO;
                btn.titleLabel.font = [UIFont systemFontOfSize:15];
                NSString *title = [NSString stringWithFormat:@"重新获取（%ds）",timeout];
                [btn setBackgroundColor:[UIColor lightGrayColor]];
                [btn setTitle:title forState:UIControlStateNormal];
                
            });
            timeout--;
            
        }
    });
    dispatch_resume(_timer);
}