如何将值从 SceneDelegate 文件传输到 ViewController (Swift 5)答案

【问题标题】：How to transfer a value from a SceneDelegate file to a ViewController (Swift 5)如何将值从 SceneDelegate 文件传输到 ViewController (Swift 5)
【发布时间】：2020-08-18 14:20:42
【问题描述】：

在其中一个 SceneDelegate 方法中，我想为另一个 ViewController 中的变量赋值。我怎样才能做到这一点？总是为零。我尝试了不同的方法，但由于某种原因它们不起作用，我想使用完成处理程序，但似乎我无法在 SceneDelegate 方法中做到这一点

class SceneDelegate: UIResponder, UIWindowSceneDelegate {
        
var viewController: ViewController?
   ...
   //This method works when I click on a cell
   func scene(_ scene: UIScene, openURLContexts URLContexts: Set<UIOpenURLContext>) {
   if let url = URLContexts.first?.url {

      let oauthCompletion: DropboxOAuthCompletion = {
      if let authResult = $0 {
      switch authResult {
      case .success:
         self.dropboxManager.fetchFiles()
         UserDefaults.standard.set(true, forKey:"userAuthorizedInDropbox")
    
         //I want to assign a value here
         self.viewController?.someString = "Some Text"
    
         print("Success! User is logged into Dropbox.")
      case .cancel:
          print("Authorization flow was manually canceled by user!")
      case .error(_, let description):
          print("Error: \(String(describing: description))")
          }
      }
   }
   DropboxClientsManager.handleRedirectURL(url, completion: oauthCompletion)
  }
} 

...
class ViewController: UIViewController {
   ...
   //But it's still nil
   var someString: String?
   ...
   func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
   dropboxManager.openDropboxAutorization(controller: self)
   }
}

.....
class MainTabBarController: UITabBarController {
let viewController: ViewController = ViewController.loadFromStoryboard()
   override func viewDidLoad() {
        super.viewDidLoad()
    viewControllers = [
            generateVC(rootViewController: viewController, image:           nil, title: "Import")
            ...
        ]

private func generateVC(rootViewController: UIViewController, image: UIImage?, title: String) -> UIViewController {
        let navigationVC = UINavigationController(rootViewController: rootViewController)
        navigationVC.tabBarItem.image = image
        navigationVC.tabBarItem.title = NSLocalizedString(title, comment: "")
        rootViewController.navigationItem.title = NSLocalizedString(title, comment: "")
        return navigationVC
    }
   }
...
}

【问题讨论】：

显示分配viewController: ViewController?的时间和地点。
我在标签栏控制器中执行此操作。我在问题中添加了代码

标签： ios swift uiscenedelegate

【解决方案1】：

您可以从场景委托中的rootViewController 访问您想要的ViewController。在以下示例中，我正在考虑您所需的视图控制器位于标签栏控制器的第一个标签中。

if let tabbarController = self.window?.rootViewController as? UITabBarController,
   let navigationController = tabbarController.viewControllers?.first as? UINavigationController,
   let desiredController = navigationController.viewControllers.first as? ViewController {
       desiredController.someString = "some value"
}

但在我看来，这不是推荐的方法，因为可能有很多情况可能取决于应用程序或导航堆栈的状态。

你可以做的是在你想要的ViewController 中添加一个观察者，然后像这样从SceneDelegate 发布通知：

NotificationCenter.default.post(name: Notification.Name(rawValue: "someeventname"), object: "some value")

你可以像这样添加和监听观察者：

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
        NotificationCenter.default.addObserver(self, selector: #selector(someEventNotificationReceived(notification:)), name: Notification.Name(rawValue: "someeventname"), object: nil)
    }
    
    deinit {
        NotificationCenter.default.removeObserver(self, name: Notification.Name(rawValue: "someeventname"), object: nil)
    }

    @objc func someEventNotificationReceived(notification: Notification) {
        if let value = notification.object as? String {
            //handle the event here
        }
    }
}

【讨论】：