UIAlert故障

如果用户点击按钮并且标签文本为0,我将尝试显示UIAlert。单击按钮后,我希望按钮将标签文本更改为0。当我尝试这样做时,UIAlert会在我不想的时候出现。下面是我的按钮代码:

@IBAction func checkButton(sender: UIButton) {

    if (currentCountLabel == "0"){

        let alert = UIAlertView()
        alert.title = "Alert"
        alert.message = "You must type in an answer in order to check it"
        alert.addButtonWithTitle("Understood")
        alert.show()

    }

    currentCount *= 0
    currentCountLabel.text = "\(currentCount)"

}

如何使用按钮将标签的文本更改为0,但在文本更改时不显示错误?

提前感谢。