【iOS学步】点击获取验证码倒计时功能

先记一下踩的弱智坑：
倒计时事件中，计时结束，按钮的状态应设置为 UIControlStateNormal，竟然错写成了 UIControlStateDisable，还调试了半天，只能说无地自容了。

- (void)secondChangeAction {
    NSLog(@"倒计时开始");
    if (self.secondsCount > 0) {
        _getCaptchaBtn.layer.borderColor = [UIColor colorWithHexString:@"979797"].CGColor;
        self.getCaptchaBtn.enabled = NO;
        [self.getCaptchaBtn setTitle:[NSString stringWithFormat:@"%lds",self.secondsCount] forState:UIControlStateNormal];
        self.secondsCount--;
    }
    else {
        _getCaptchaBtn.layer.borderColor = kAppBaseGreenColor.CGColor;
        self.getCaptchaBtn.enabled = YES;
        [_getCaptchaBtn setTitle:[NSString stringWithFormat:@"重新获取验证码"] forState:UIControlStateNormal]; //错写为Disable了
        self.secondsCount = 0;
        [self.getCodetimer invalidate];
        self.getCodetimer = nil;
    }
}