Ios 尝试开始从一个viewcontroller向另一个viewcontroller传输数据时出现断点错误

我正在尝试将此数据“用户名”传输到另一个视图控制器。我的大部分工作正常，但在

displayViewController.usernameintered=username.text上有一个断点错误

以下是我的其他视图控制器的代码：

import UIKit

class ViewController: UIViewController {

@IBOutlet weak var username: UITextField!

@IBAction func loginPressed(_ sender: Any) {

    print("Username entered is  \(username.text)")

    let displayViewController = storyboard?.instantiateViewController(withIdentifier: "DisplayViewController") as! DisplayViewController

    displayViewController.usernameEntered = username.text

    self.navigationController?.pushViewController(displayViewController, animated: true)

}

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

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

任何关于为什么会发生这种情况的见解都将不胜感激
 检查
username.text
不应为
nil

&确保您已连接
username并从情节提要中输入了
标签插座。
您的
username.text
可能为零。你先检查过它的值吗？尝试在此处放置可选绑定是否已将
usernamelab
连接到情节提要中的文本字段？
import UIKit

class DisplayViewController: UIViewController {

var usernameEntered:String?

@IBOutlet weak var usernameLabel: UILabel!


override func viewDidLoad() {
    super.viewDidLoad()

    // Do any additional setup after loading the view.
}

override func viewDidAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    if let usernameToDisplay = usernameEntered
    {
        self.usernameLabel.text = usernameToDisplay
    }

}

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

}