SceneDelegate中出现‘couldn't find window in scope’错误，求解决方案

问题场景 #

通常couldn't find window in scope错误多出现于AppDelegate.swift中，原因是新增的Scene Delegate，但我却在Scene Delegate中遇到了该问题。以下是我的代码：

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
        // If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
        // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).
        guard let _ = (scene as? UIWindowScene) else { return }
        
        let storyboard = UIStoryboard(name: "Main", bundle: nil)

        if (UserDefaults.standard.bool(forKey: "ISRemember")) {
            print(UserDefaults.standard.bool(forKey: "ISRemember"))
            let mainTabBarController = storyboard.instantiateViewController(identifier: "tabbar")
            window?.rootViewController = mainTabBarController
        }
        else {
            
        }
    }

已尝试清理Xcode的构建文件夹、重启Xcode甚至重启Mac，但问题仍未解决。

可行解决思路 #

• 确认SceneDelegate类中存在window属性
  默认Xcode生成的SceneDelegate会自带var window: UIWindow?属性，如果你的类里缺失，手动添加到类声明中：

  class SceneDelegate: UIResponder, UIWindowSceneDelegate {
      var window: UIWindow? // 必须存在该属性
      
      // 其他方法实现...
  }
  

• 正确初始化并绑定window到UIWindowScene
  原代码仅判断了scene类型，未初始化window并关联到当前场景，修改代码如下：

  guard let windowScene = scene as? UIWindowScene else { return }
  // 初始化window并关联到当前windowScene
  window = UIWindow(windowScene: windowScene)
  
  let storyboard = UIStoryboard(name: "Main", bundle: nil)
  if UserDefaults.standard.bool(forKey: "ISRemember") {
      let mainTabBarController = storyboard.instantiateViewController(identifier: "tabbar")
      window?.rootViewController = mainTabBarController
      // 让window成为可见状态
      window?.makeKeyAndVisible()
  }
  

• 检查Storyboard与Info.plist配置
  确认Main.storyboard中已设置正确的初始ViewController，同时检查Info.plist里的Scene Manifest配置，确保SceneDelegate被正确关联到应用场景，避免因配置错误导致window无法自动初始化。

• 补全UserDefaults默认值（辅助优化）
  为避免ISRemember键未初始化导致的逻辑异常，可在应用启动时默认设置该键值：

  // 可放在AppDelegate的application(_:didFinishLaunchingWithOptions:)方法中
  if UserDefaults.standard.object(forKey: "ISRemember") == nil {
      UserDefaults.standard.set(false, forKey: "ISRemember")
  }
  

内容的提问来源于stack exchange，提问作者Youssef Yasser