swift - 警报消息无法出现

Question

当用户触摸“开始”以启动计时器且 3 个必需的文本字段中的任何一个或全部为空时，我一直在尝试弹出警报消息。模拟器中没有弹出任何警报消息。

@IBAction func start(_ sender: Any) {
//the following code produces an alert if any of the specified text fields are blank when the "start" button is pressed
if medName.text == nil || dose.text == nil || freq.text == nil {

    let alertController = UIAlertController(title: "Field(s) must be filled in!", message: "Please complete all fields.", preferredStyle: UIAlertControllerStyle.alert)

    alertController.addAction(UIAlertAction(title: "OK", style: .default, handler: { (action)
        in
        self.dismiss(animated: true, completion: nil)}))

    self.present(alertController, animated: true, completion: nil)

    } else {

        timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(SecondViewController.decreaseTimer), userInfo: nil, repeats: true)

    let itemsObject = UserDefaults.standard.object(forKey: "cellContent")

    var cellContent:[String]

    if let tempItems = itemsObject as? [String] {

        cellContent = tempItems

        cellContent.append(medName.text!)

    } else {

        cellContent = [medName.text!]

    }

    UserDefaults.standard.set(cellContent, forKey: "cellContent")
    //the following code clears the text within each of the specified text fields when start is pressed
    medName.text = ""
    dose.text = ""
    freq.text = ""
    }
}

Answer 1

当文本字段为空并且没有文本时，它不是 nil，这就是您不输入 if 语句的原因。执行此检查，而不是检查文本是否为 "":

if medName.text == "" || dose.text == "" || freq.text == ""