通过在多个控制器之间准备segue传递特定键/值

Question

我尝试通过准备（for segue）方法传递数据，但无法在ReceiverViewController中传递数据。我不知道我会更好地通过整个事件，不知道是否有可能。 我是Swift的新手，这是我的第一次尝试，任何建议都会受到欢迎。

我想使用的类如下 - UserClass.swift：

class User { 
    var firstname: String 
    var lastname: String 
    var role: Int 

    init(firstname: String, lastname: String, role: Int) { 
     self.firstname = firstname 
     self.lastname = lastname 
     self.role = role 
    } 

} 

我对FirstViewController.swift

准备方法

override func prepare(for segue: UIStoryboardSegue, sender: Any?) { 
    if segue.identifier == "loadBoard" { 
     if let dVC = segue.destination as? ReceiverViewController { 
      dVC.code?.firstname = anotherValue 

      //Following show me nil 
      print("Sent data \(dVC.code?.firstname)") 
     } 
    } 
} 

这里是我试图让数据 - ReceiverViewController .swift：

var code: User? 

if let test = self.code?.firstname { 
    self.categoryLabel.text = code?.firstname 
    print(code) 
} else { 
    print("Something wrong") 
} 

Answer 1

prepareForSegue在目标viewControll之前被调用呃的viewDidLoad。如果您在ReceiverViewController的viewDidLoad期间依赖于将代码属性设置为用户，那么您的方法将无法工作。

因此，您需要在prepareForSegue期间设置ReceiverViewController的code属性，或者使用firstname设置ReceiverViewController的另一个属性，然后在ReceiverViewController的viewDidLoad期间获取分配给代码的firstname。

Answer 2

在prepareForSegue中，您试图在code: User?上设置一个属性，该属性是未初始化的对象。你可以做的反而是通过在调用performSegue初始化的User对象，然后执行以下操作：

override func prepare(for segue: UIStoryboardSegue, sender: Any?) { 
    if segue.identifier == "loadBoard" { 
     if let dVC = segue.destination as? ReceiverViewController, 
      let user = sender as? User { 
       dVC.code = user 

     } 
    } 
} 

Answer 3

这是如何从一个控制器发送和接收数据到其他的例子。

prepareForSegue在加载目标控制器之前调用。 因此，目标控制器上的元素无法在发送控制器内设置。 这里的方法是设置一些其他变量与要发送的数据。 在目标视图控制器中，处理viewWillAppear中的数据。

发送控制器：

// https://github.com/ryantxr/legendary-potato 
// ViewController.swift 
// data-share 
// 
// Created by ryan teixeira on 3/21/16. 
// Copyright © 2016 Ryan Teixeira. All rights reserved. 
// 
import UIKit 

class ViewController: UIViewController { 

    @IBOutlet weak var helloTextField: UITextField! 
    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. 
    } 
    // In a storyboard-based application, you will often want to do a little preparation before navigation 
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) { 
     // Get the new view controller using segue.destinationViewController. 
     // Pass the selected object to the new view controller. 
     if segue.identifier == "showDetail" { 
      print("detail segue") 
      let destinationController = segue.destinationViewController as! DetailViewController 
      destinationController.helloText = helloTextField.text 
     } 
    } 
} 

接收视图控制器：

// https://github.com/ryantxr/legendary-potato 
// DetailViewController.swift 
// data-share 
// 
// Created by ryan teixeira on 3/21/16. 
// Copyright © 2016 Ryan Teixeira. All rights reserved. 
// 
import UIKit 

class DetailViewController: UIViewController { 

    var helloText: String? 
    @IBOutlet weak var helloLabel: UILabel! 
    override func viewDidLoad() { 
     super.viewDidLoad() 

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

    override func viewWillAppear(animated: Bool) { 
     helloLabel.text = helloText 
    } 

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


    /* 
    // MARK: - Navigation 
    // In a storyboard-based application, you will often want to do a little preparation before navigation 
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) { 
     // Get the new view controller using segue.destinationViewController. 
     // Pass the selected object to the new view controller. 
    } 
    */ 

}