如何使用segues在视图控制器之间传输数据

我试图使用prepare(for segue:)函数传递数据，但它在第二个VC中显示为零。我做错了什么？如何使用segues在视图控制器之间传输数据

class ViewController: UIViewController { 

    var first : [String] = [] 

    @IBOutlet weak var passField: UITextField! 
    @IBOutlet weak var userID: UITextField! 

    override func viewDidLoad() { 
     super.viewDidLoad() 
    } 

    @IBAction func login(_ sender: Any) { 
     let user : String = self.userID.text! 
     let password : String = self.passField.text! 

     if user != "" && password != "" { 
      let postString = ["username":user, “password”: password] 
      var request = URLRequest(url:URL(string:"http://mydomainhere.com/api/login")!) 
      request.httpMethod = "POST" 
      request.httpBody = try! JSONSerialization.data(withJSONObject: postString, options:.prettyPrinted) 
      let task = URLSession.shared.dataTask(with: request) { (data: Data?, response: URLResponse?, error: Error?) in 
       if error != nil { 
        print("error=\(error)") 
        return 
       } 

       do { 
        if let json = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? [String: Any] { 
         let firstName = json["first_name"] as? String 
         let lastName = json["last_name"] as? String 
         self.first.append(firstName!) //putting into Array 
         self.performSegue(withIdentifier: "loginSegue", sender: self) 
        } 
       } catch { 
        print(error) 
       } 
      } 
     } 
    } 

    // data transfer to another controller 
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) { 
     if segue.identifier == "loginSegue" { 
      let secondController = segue.destination as? SecondVC 
      secondController?.name = first //passing to next VC //* here having the issue its not passing the data to next VC 
      print(first) // here first is printing perfectly 
     } 
    } 
} 


// second View Controller 
class SecondVC: UIViewController { 

    var menu_vc : MenuViewController! 
    var name : [String]? // passing to this Array 

    override func viewDidLoad() { 
     super.viewDidLoad() 
     print(name) // here printing nil 
    } 
}

来源

2017-06-04 Akash Savediya

在prepareForSegue中设置一个断点，然后逐步查看发生了什么。视图控制器downcast可能失败。 – Paulw11

@ Paulw11感谢您的回复，但我没有得到你。你能不能给我一些建议我实际需要做的事情。 –

我不能建议代码。你所看到的代码通常是正确的。了解如何使用内置于Xcode中的功能强大的调试器来浏览您的应用，并了解它在做什么。 – Paulw11

正如@Sweeper建议，它很可能是你的目的地视图控制器嵌入UINavigationViewController，因此你segue.destination是实际上是一个UINavigationViewController，而不是SecondVC。

你可以试试这个代码：

override func prepare(for segue: UIStoryboardSegue, sender: Any?) { 
    var destinationViewController = segue.destination 
    if let navigationController = destinationViewController as? UINavigationController { 
     destinationViewController = navigationController.visibleViewController ?? destinationViewController 
    } 
    if let secondController = destinationViewController as? SecondVC { 
     secondController?.name = first 
    } 
}

当然代码的前四行可以在适当的功能（如果UIViewController中的延伸甚至更好）进行重构。

如果解决了这个问题，您可以观看cs193p Stanford iOS课程以获取更多详细信息。特别是手表https://www.youtube.com/watch?v=HQrXM2zUPvY&index=6&list=PLPA-ayBrweUz32NSgNZdl0_QISw-f12Ai从30:20开始。

来源

2017-06-04 09:04:48 ciamic

很棒。完美地工作。谢谢！ –

一切似乎完美与下面的代码片段

var first : [String] = [] 

@IBAction func btnTapped(_ sender: Any) { 
    let firstName = "iOS Geek" 
    self.first.append(firstName) 

    self.performSegue(withIdentifier: "MovetoSecVC", sender: self) 
} 


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

     let secVC = segue.destination as! SecondVC 
     secVC.name = first 
     print(first) // it'll print here ["iOS Geek"] 
    } 
} 

// Your Second View Controller 

class SecondVC: UIViewController { 

var menu_vc : MenuViewController! 
var name : [String]? // passing to this Array 

override func viewDidLoad() { 
    super.viewDidLoad() 

    print(name!) // it'll print here ["iOS Geek"] 
    } 
}

来源

2017-06-04 06:49:28

如何使用segues在视图控制器之间传输数据

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