Ios 在视图控制器之间传递数据会产生零

我是一名新的程序员，在控制器之间传递数据时遇到了困难，我知道这些论坛会问这个问题，但上传的代码比我的复杂得多，我很难理解，所以我会上传我写的几行代码。我想允许两名玩家在我的应用程序中输入他们的名字，然后单击开始游戏。当按下“开始游戏”按钮时，会将他们带到一个新的视图控制器，该控制器的名称类似于Joe Bloggs vs John Doe，如果我将变量设置为全局变量，我可以实现这一点，但我的理解是，这是一种糟糕的做法，因此当我尝试编写相同的代码，将变量保留在视图控制器中时，每次都会通过nil，我不确定我做错了什么？这是我的几行代码，我希望有人能回答我做错了什么

视图控制器：

import UIKit

class ViewController: UIViewController {

    var playerOneName: String!
    var playerTwoName: String!

    @IBOutlet weak var playerOneTextField: UITextField!
    @IBOutlet weak var playerTwoTextField: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    @IBAction func startGameButton(_ sender: Any) {

        playerOneName = playerOneTextField.text!
        playerTwoName = playerTwoTextField.text!

    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "segue" {

            let destinationVC = segue.destination as! GameViewController
            destinationVC.playerOne.text = playerOneName
            destinationVC.playerTwo.text = playerTwoName
        }
    }

}

import UIKit

class GameViewController: UIViewController {

    @IBOutlet weak var playerOne: UILabel!
    @IBOutlet weak var playerTwo: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.

    }

}

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "segue" {

            let destinationVC = segue.destination as! GameViewController
            destinationVC.playerOneName = playerOneName
            destinationVC.playerTwoName = playerTwoName
        }
    }

GameViewController：

import UIKit

class ViewController: UIViewController {

    var playerOneName: String!
    var playerTwoName: String!

    @IBOutlet weak var playerOneTextField: UITextField!
    @IBOutlet weak var playerTwoTextField: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    @IBAction func startGameButton(_ sender: Any) {

        playerOneName = playerOneTextField.text!
        playerTwoName = playerTwoTextField.text!

    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "segue" {

            let destinationVC = segue.destination as! GameViewController
            destinationVC.playerOne.text = playerOneName
            destinationVC.playerTwo.text = playerTwoName
        }
    }

}

import UIKit

class GameViewController: UIViewController {

    @IBOutlet weak var playerOne: UILabel!
    @IBOutlet weak var playerTwo: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.

    }

}

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "segue" {

            let destinationVC = segue.destination as! GameViewController
            destinationVC.playerOneName = playerOneName
            destinationVC.playerTwoName = playerTwoName
        }
    }

---

在加载控制器的视图之前，您的插座不会初始化。然而，赛格发生在这之前

---

最好的解决方案是将两个字符串属性放入

GameViewController

中，并使用这些属性从第一个控制器接收数据。然后，在

viewdiload

中更新标签文本。您不应该直接从另一个视图控制器设置标签文本，而是在

gameviewdiload

中创建变量来存储标签文本，在segue中更改这些变量，然后在目标控制器的

viewdiload

方法中更改标签。请参阅下面的代码

class GameViewController: UIViewController {

    @IBOutlet weak var playerOne: UILabel!
    @IBOutlet weak var playerTwo: UILabel!

    var playerOneName:String?
    var playerTwoName:String?

    override func viewDidLoad() {
        super.viewDidLoad()
        playerOne.text = playerOneName
        playerTwo.text = playerTwoName
        // Do any additional setup after loading the view.

    }

}

在ViewController中：

import UIKit

class ViewController: UIViewController {

    var playerOneName: String!
    var playerTwoName: String!

    @IBOutlet weak var playerOneTextField: UITextField!
    @IBOutlet weak var playerTwoTextField: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    @IBAction func startGameButton(_ sender: Any) {

        playerOneName = playerOneTextField.text!
        playerTwoName = playerTwoTextField.text!

    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "segue" {

            let destinationVC = segue.destination as! GameViewController
            destinationVC.playerOne.text = playerOneName
            destinationVC.playerTwo.text = playerTwoName
        }
    }

}

import UIKit

class GameViewController: UIViewController {

    @IBOutlet weak var playerOne: UILabel!
    @IBOutlet weak var playerTwo: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.

    }

}

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "segue" {

            let destinationVC = segue.destination as! GameViewController
            destinationVC.playerOneName = playerOneName
            destinationVC.playerTwoName = playerTwoName
        }
    }

---

在初始化控制器之前，不能设置

@IBOutlets

的属性。 您需要存储像

String这样的值在第二视图控制器中。和init
@IBOutlets
，例如在
viewDidLoad
方法中使用它们

将
GameViewController
代码更改为：

import UIKit

class GameViewController: UIViewController {
    @IBOutlet weak var playerOne: UILabel!
    var playerOneName: String!     

    @IBOutlet weak var playerTwo: UILabel!
    var playerTwoName: String!

    override func viewDidLoad() {
        super.viewDidLoad()

        playerOne.text = playerOneName
        playerTwo.text = playerTextName
        // Do any additional setup after loading the view.
    }
}

和
ViewController
中的
prepare
：

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "segue" {
        let destinationVC = segue.destination as! GameViewController
        destinationVC.playerOneName = playerOneName
        destinationVC.playerTwoName = playerTwoName
    }
}

希望有帮助
您检查过文本字段是否正确映射到变量了吗？如果在按钮回调之前调用了
prepare（for:sender:）
，怎么办？因为执行
destinationVC.playeron.text=playeroname
时
playeron
是
nil
。换句话说，
IBOulet
尚未加载。创建一个
String
属性，该属性将保存
playername
值。在
viewdiload（）
上，在Objective-C中将
playerne.text
设置为它。但原因相同：或