倒计时方法

    //ButtonCountDown.h
    +(void)countDownButton:(UIButton *)sender withTitle:(NSString *)title withBackgroundColor:(UIColor* )color withCountDownTime:(NSInteger)timeNum;

---

    //ButtonCountDown.m
    +(void)countDownButton:(UIButton *)sender withTitle:(NSString *)title withBackgroundColor:(UIColor* )color withCountDownTime:(NSInteger)timeNum{
__block NSInteger time = timeNum; //倒计时时间

//    [sender setTitle:@"重新发送" forState:UIControlStateNormal];
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
//设置按钮的样式
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(), ^{
            [sender setTitleColor:color forState:UIControlStateNormal];
            [sender setTitle:title forState:UIControlStateNormal];
            sender.userInteractionEnabled = YES;
        });
    }else{
        int seconds = time % 60;
        dispatch_async(dispatch_get_main_queue(), ^{
            //设置按钮显示读秒效果
            [sender setTitle:[NSString stringWithFormat:@"%.2dS", seconds] forState:UIControlStateNormal];
            [sender setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
            sender.userInteractionEnabled = NO;
        });
        time--;
    }
});
dispatch_resume(_timer);
}