ios 验证码倒计时

实际开发中，我们需要用到验证码这个功能，那么问题就来了，怎么实现Button的动态显示倒计时呢？效果图如下：

示意图.png

实现代码如下：

//获取验证码
-(void)getVerifyCode:(UIButton *)sender{
    __block int timeout = 60; //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(), ^{
                sender.userInteractionEnabled = YES;
                sender.backgroundColor = [UIColor whiteColor];
                [sender setTitle:@"再次获取验证码" forState:UIControlStateNormal];
            });
        }
        else
        {
            dispatch_async(dispatch_get_main_queue(), ^{
                sender.userInteractionEnabled = NO;
                sender.backgroundColor = [UIColor lightGrayColor];
                [sender setTitle:[NSString stringWithFormat:@"%ds",timeout] forState:UIControlStateNormal];
            });
            
            timeout--;
            
        }
    });
    dispatch_resume(timer);
}