ios - 准备 segue 函数无法将数据传递给另一个 VC Swift，

Question

我正在尝试将警报文本字段中的数据传递给另一个 VC 的变量。
这是我的警报 Controller 。

let alert = UIAlertController(title: "Download URL", message: "", preferredStyle: .alert)
    
    let action = UIAlertAction(title: "Download", style: .default) { (action) in
        
        guard let textField = alert.textFields?.first else {return}
        
        self.ayb = textField.text ?? "Blank"
        
        UserDefaults.standard.set(self.ayb, forKey: "urlString")
        
        self.performSegue(withIdentifier: "segAdd", sender: self)
    }
    let secondAction = UIAlertAction(title: "Cancel", style: .cancel, handler: nil)
    
    alert.addTextField { (actionTextField) in
        actionTextField.placeholder = "Paste link here"
    }
    
    alert.addAction(action)
    alert.addAction(secondAction)
    present(alert, animated: true, completion: nil)
}

这是我用于传递数据的准备函数。

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "segAdd" {
        let destinationVC = tabBarController?.viewControllers?[0] as? BrowserWebViewController
        destinationVC?.urlFromDownloads = self.ayb
        print("The value of destinationVC?.urlFromDownloads is \(destinationVC?.urlFromDownloads)")
    }
}

在控制台中，它会写“destinationVC?.urlFromDownloads 的值是\Optional("Text I typed in textField")”。
但在 BrowserWebViewController 我的 "urlFromDownloads" is = ""(which is default) .
注意:Segue 的名字是真实的。

Answer 1

首先，不要声明额外的属性或将值保存到 UserDefaults您可以在 sender 中传递字符串范围

let action = UIAlertAction(title: "Download", style: .default) { (action) in
    guard let textField = alert.textFields?.first else {return}
    self.performSegue(withIdentifier: "segAdd", sender: textField.text!)
}

您确定目标 View Controller 的方法是错误的。询问 segue对于destination .你可以强制向下转换类型。如果 segue 设计正确，则代码不得崩溃。

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "segAdd" {
        let destinationVC = segue.destination as! BrowserWebViewController
        destinationVC.urlFromDownloads = sender as! String
        print("The value of destinationVC?.urlFromDownloads is \(destinationVC.urlFromDownloads)")
    }
}