将数据从一个视图控制器发送到另一个不起作用

Question

我正在尝试将一些数据从一个视图控制器发送到另一个视图控制器。但我似乎无法让这段代码工作！它应该将标签更改为传递给它的变量，但不会更改任何内容。

ViewController.swift

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "SVCSegue" {
        let controller = segue.destination as! SecondViewController
        if let user = FIRAuth.auth()?.currentUser {
            controller.email = user.email
        }
    }
}

SecondViewController.swift

@IBOutlet weak var usernameLabel: UILabel!

    var email:String!

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.

        self.usernameLabel.text = self.email

    }

编辑我在override func prepare之后也有这个代码

@IBAction func loginAction(_ sender: Any) {

        if self.emailField.text == "" || self.passwordField.text == "" {
            let alertController = UIAlertController(title: "Oops!", message: "Please put in an email and password.", preferredStyle: .alert)
            let defaultAction = UIAlertAction(title: "Ok", style: .cancel, handler: nil)

            alertController.addAction(defaultAction)

            self.present(alertController, animated: true, completion: nil)
        } else {
            FIRAuth.auth()?.signIn(withEmail: self.emailField.text!, password: self.passwordField.text!, completion: { (user, error) in
                if error == nil {
                    self.emailField.text = ""
                    self.passwordField.text = ""
                } else {
                    let alertController = UIAlertController(title: "Oops!", message: error?.localizedDescription, preferredStyle: .alert)
                    let defaultAction = UIAlertAction(title: "Ok", style: .cancel, handler: nil)

                    alertController.addAction(defaultAction)
                }
            })
        }
    }

Answer 1

我不确定，但是根据在序列期间调用 SecondViewController 的不同生命周期函数的时间，可能在执行准备代码之前调用了 viewDidLoad。

尝试为电子邮件设置一个默认值，以便您可以使用该值。另外，在 prepare 方法的 else 部分中将 email 值设置为其他值，以查看是否是 if 条件失败。

Answer 2

@IBAction func loginAction(_ sender: Any) {

        if self.emailField.text == "" || self.passwordField.text == "" {
            let alertController = UIAlertController(title: "Oops!", message: "Please put in an email and password.", preferredStyle: .alert)
            let defaultAction = UIAlertAction(title: "Ok", style: .cancel, handler: nil)

            alertController.addAction(defaultAction)

            self.present(alertController, animated: true, completion: nil)
        } else {
            FIRAuth.auth()?.signIn(withEmail: self.emailField.text!, password: self.passwordField.text!, completion: { (user, error) in
                if error == nil {
               let sb = UIStoryboard(name: "StoryBoardName", bundle: nil)
    let secVC = sb.instantiateViewController(withIdentifier: "ViewControllerIdentifier") as! SecondViewController
                 if let userValue = FIRAuth.auth()?.currentUser {
                        secVC.email = userValue.email!
                    }
       self.navigationController?.pushViewController(secVC, animated: true)
                } else {
                    let alertController = UIAlertController(title: "Oops!", message: error?.localizedDescription, preferredStyle: .alert)
                    let defaultAction = UIAlertAction(title: "Ok", style: .cancel, handler: nil)

                    alertController.addAction(defaultAction)
                }
            })
        }
    }

I have made change in loginAction() that is navigate to SecondViewController and pass data of user

Try above code , Hope this help you and solved your issue.