如何使警报中的取消按钮取消操作？

Question

如您所见，我发出了警报，但无论我在弹出警报时是否单击“否”按钮或“是的，我确定”按钮，应用程序都会添加该项目。

我的目标是做出“否”动作，取消动作，这样输入就不会被添加。你能告诉我怎么做吗？

import UIKit

class SecondViewController: UIViewController, UITextFieldDelegate {
    @IBOutlet weak var input: UITextField!

    @IBAction func addItem(_ sender: Any)
    {
        createAlert(title: "That's a good grail!", message: "Are you sure you want to add this grail?")

        if (input.text != "")
        {
            list.append(input.text!)
            input.text = ""
        }
    }

    override func viewDidLoad()
    {
        super.viewDidLoad()

        self.input.delegate = self
    }

    //HIDE KEYBOARD:
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        self.view.endEditing(true)
    }

    //PRESSES RETURN KEY:
    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        input.resignFirstResponder()
        return true
    }

    func createAlert (title:String, message:String)
    {
        let alertController = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.alert)

        //CREATING OK BUTTON

        let OKAction = UIAlertAction(title: "Yes, I'm sure!", style: .default) { (action:UIAlertAction!) in

            // Code in this block will trigger when OK button tapped.
            print("Ok button tapped");

        }
        alertController.addAction(OKAction)

        // Create Cancel button
        let cancelAction = UIAlertAction(title: "No!", style: .cancel) { (action:UIAlertAction!) in
            print("Cancel button tapped");
        }
        alertController.addAction(cancelAction)

        // Present Dialog message
        self.present(alertController, animated: true, completion:nil)
    }
}

编辑：

现在的代码是这样的，谢谢：

导入 UIKit

类 SecondViewController: UIViewController, UITextFieldDelegate {

@IBOutlet weak var input: UITextField!

@IBAction func addItem(_ sender: Any)
{
    createAlert(title: "That's a good grail!", message: "Are you sure you want to add this grail?")

}



override func viewDidLoad()
{
    super.viewDidLoad()

    self.input.delegate = self
}



override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}


//HIDE KEYBOARD:
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    self.view.endEditing(true)
}

//PRESSES RETURN KEY:
func textFieldShouldReturn(_ textField: UITextField) -> Bool {
    input.resignFirstResponder()
    return true
}


func createAlert (title:String, message:String)
{
    let alertController = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.alert)

    //CREATING OK BUTTON

    let OKAction = UIAlertAction(title: "Yes, I'm sure!", style: .default) { (action:UIAlertAction!) in

        // Code in this block will trigger when OK button tapped.
        print("Ok button tapped");
        if (self.self.input.text != "")
        {
            list.append(self.input.text!)
            self.input.text = ""
        }

    }
    alertController.addAction(OKAction)

    // Create Cancel button
    let cancelAction = UIAlertAction(title: "No!", style: .cancel) { (action:UIAlertAction!) in
        print("Cancel button tapped");
    }
    alertController.addAction(cancelAction)

    // Present Dialog message
    self.present(alertController, animated: true, completion:nil)
}

}

Answer 1

只需将添加项目的代码放到 OK 闭包中即可：

class SecondViewController: UIViewController, UITextFieldDelegate {

@IBOutlet weak var input: UITextField!

@IBAction func addItem(_ sender: Any)
{
    createAlert(title: "That's a good grail!", message: "Are you sure you want to add this grail?")
}

override func viewDidLoad()
{
    super.viewDidLoad()

    self.input.delegate = self
}



override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}


//HIDE KEYBOARD:
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    self.view.endEditing(true)
}

//PRESSES RETURN KEY:
func textFieldShouldReturn(_ textField: UITextField) -> Bool {
    input.resignFirstResponder()
    return true
}


func createAlert (title:String, message:String)
{
    let alertController = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.alert)

    //CREATING OK BUTTON

    let OKAction = UIAlertAction(title: "Yes, I'm sure!", style: .default) { (action:UIAlertAction!) in

        // Code in this block will trigger when OK button tapped.
     if (input.text != "")
     {
        list.append(input.text!)
        input.text = ""
     }
        print("Ok button tapped");

    }
    alertController.addAction(OKAction)

    // Create Cancel button
    let cancelAction = UIAlertAction(title: "No!", style: .cancel) { (action:UIAlertAction!) in
        print("Cancel button tapped");
    }
    alertController.addAction(cancelAction)

    // Present Dialog message
    self.present(alertController, animated: true, completion:nil)
}
}

Answer 2

在显示UIAlertController 之后，无论如何您都在addItem(_ :) 方法中添加input.text。

因此，如果您想避免始终添加 input.text，并且仅在点击 OK 按钮时，您应该在创建它时将其包含在该操作的关闭中，并在呈现 UIAlertController 后将其删除

let OKAction = UIAlertAction(title: "Yes, I'm sure!", style: .default) { [weak self] _ in

        guard let selfStrong = self else {
            return
        }

        // Code in this block will trigger when OK button tapped.
        if (selfStrong.input.text != "") {
           selfStrong.list.append(input.text!)
           selfStrong.input.text = ""
        }
}

对于取消按钮，您不需要任何操作关闭，除非您也想在点击取消按钮时执行某些操作。

希望对你有帮助。

Answer 3

您没有在单击“是的，我确定”按钮时附加该项目。删除 @IBAction func addItem(_ sender: Any) 方法中的以下代码并将其放入 OKAction 处理程序块中。

if (input.text != "")
    {
        list.append(input.text!)
        input.text = ""
    }

这样做：

@IBAction func addItem(_ sender: Any)
    {
        createAlert(title: "That's a good grail!", message: "Are you sure you want to add this grail?")


}

Inside 方法：func createAlert(title:String, message:String)（在此处添加附加代码）

let OKAction = UIAlertAction(title: "Yes, I'm sure!", style: .default) { (action:UIAlertAction!) in
        // Code in this block will trigger when OK button tapped.
        print("Ok button tapped");
    if (input.text != "")
    {
        list.append(input.text!)
        input.text = ""
    }
}