//开始倒计时
-(void)openCountdown{
    __block NSInteger time = 59; //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
                [_authCodeBtn setTitle:@"重新发送" forState:UIControlStateNormal];
                [_authCodeBtn setTitleColor:[UIColor lightGrayColor] forState:UIControlStateNormal];
                [_authCodeBtn setAlpha:1.0];
                 _authCodeBtn.userInteractionEnabled = YES;
            });
        }else{
            int seconds = time % 60;
            dispatch_async(dispatch_get_main_queue(), ^{
                //设置按钮显示读秒效果
                [_authCodeBtn setBackgroundImage:[UIImage imageNamed:@"btn_blue"] forState:UIControlStateNormal];
                [_authCodeBtn setTitle:[NSString stringWithFormat:@"%.2d", seconds] forState:UIControlStateNormal];
                [_authCodeBtn setAlpha:0.5];
                 _authCodeBtn.userInteractionEnabled = NO;
            });
            time--;
        }
    });
    dispatch_resume(_timer);
}