在转到View Controller之前为Nav Bar后退操作添加警报

Question

因此，我有一个添加项vc，对于后退按钮，我希望弹出警报以询问用户是否要继续，因为他们的信息将丢失。我已经阅读并发现可以使用此功能，但无法正常使用。在加载视图时以及返回主vc之后，将出现警报。这是代码和一些图片。谢谢。

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Answer 1

您必须以这种方式在viewDidload中添加自定义后退按钮

   override func viewDidLoad() {
            super.viewDidLoad()
            let newBackButton = UIBarButtonItem(title: "Back", style: UIBarButtonItem.Style.plain, target: self, action: #selector(self.backAction(sender:)))
            self.navigationItem.leftBarButtonItem = newBackButton

        }

这是后退按钮的操作方法，因此您可以在此处添加警报，并按以下方式添加所需的操作：

@objc func backAction(sender: UIBarButtonItem) {

    let alertController = UIAlertController(title: "Are You Sure?", message: "If You Proceed, All Data On This Page Will Be Lost", preferredStyle: .alert)
    let okAction = UIAlertAction(title: "Ok", style: .default) { (result : UIAlertAction) -> Void in
        self.navigationController?.popViewController(animated: true)
    }

    let cancelAction = UIAlertAction(title: "Cancel", style: .default, handler: nil)
    alertController.addAction(cancelAction)
    alertController.addAction(okAction)
    self.present(alertController, animated: true)
}

Answer 2

override func viewDidLoad {
        super.viewDidLoad()
        self.navigationItem.hidesBackButton = true
        let newBackButton = UIBarButtonItem(title: "Back", style: UIBarButtonItemStyle.plain, target: self, action: #selector(YourViewController.back(sender:)))
        self.navigationItem.leftBarButtonItem = newBackButton
    }

    func back(sender: UIBarButtonItem) {
        let alertController = UIAlertController(title: "Are You Sure?", message: "If You Proceed, All Data On This Page Will Be Lost", preferredStyle: .alert)
        let stayAction = UIAlertAction(title: "Stay", style: UIAlertAction.Style.default) { (result : UIAlertAction) -> Void in
          print("Stay")
        }
        let leaveAction = UIAlertAction(title: "GO Back", style: UIAlertAction.Style.default) { (result : UIAlertAction) -> Void in
           self.navigationController?.popViewController(animated: true)
        }
        self.present(alertController, animated: true)
    }