Swift 5添加SceneDelegate后根视图切换失效，登出功能异常

添加SceneDelegate并迁移AppDelegate代码后，登出功能出现异常：点击登出按钮无即时反应，但关闭并重新打开应用后，用户会被正常登出。怀疑问题出在登出函数中使用的共享代理逻辑上。

相关代码 #

首页登出按钮代码 #

@IBAction func signOutButtonTapped(_ sender: Any) {
    KeychainWrapper.standard.removeObject(forKey: "accessToken")
    KeychainWrapper.standard.removeObject(forKey: "userID")
    
    // send user to splash page
    let signInPage = self.storyboard?.instantiateViewController(withIdentifier: "splashController") as! splashViewController
    let appDelegate = UIApplication.shared.delegate
    appDelegate?.window??.rootViewController = signInPage
    
}

SceneDelegate.swift代码 #

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        
        guard let _ = (scene as? UIWindowScene) else { return }

        let accessToken: String? = KeychainWrapper.standard.string(forKey: "accessToken")
        
        // If access token exists, skip login page
        if accessToken != nil {            
            if let windowScene = scene as? UIWindowScene {
                self.window = UIWindow(windowScene: windowScene)
                let mainStoryboard:UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
                let vc = mainStoryboard.instantiateViewController(withIdentifier: "homeTabController") as! TabBarController
                self.window!.rootViewController = vc
            }        
        }    

    }
  }

问题核心：iOS 13+ 采用多场景架构后，AppDelegate不再负责窗口管理，实际窗口控制权已移交SceneDelegate。你当前的登出代码仍在尝试通过UIApplication.shared.delegate获取窗口，导致修改根控制器的操作无法作用到当前活跃窗口。

修复登出函数（单场景应用） #

直接获取当前活跃场景的SceneDelegate，更新其窗口的根控制器：

@IBAction func signOutButtonTapped(_ sender: Any) {
    KeychainWrapper.standard.removeObject(forKey: "accessToken")
    KeychainWrapper.standard.removeObject(forKey: "userID")
    
    // 获取当前活跃场景的SceneDelegate及窗口
    guard let windowScene = UIApplication.shared.connectedScenes.first as? UIWindowScene,
          let sceneDelegate = windowScene.delegate as? SceneDelegate,
          let window = sceneDelegate.window else {
        return
    }
    
    // 跳转至启动页
    let signInPage = self.storyboard?.instantiateViewController(withIdentifier: "splashController") as! splashViewController
    window.rootViewController = signInPage
    window.makeKeyAndVisible() // 确保窗口切换后可见
}

多场景支持优化（如iPad分屏） #

如果应用支持多场景，遍历所有活跃场景并统一更新根控制器：

@IBAction func signOutButtonTapped(_ sender: Any) {
    KeychainWrapper.standard.removeObject(forKey: "accessToken")
    KeychainWrapper.standard.removeObject(forKey: "userID")
    
    let signInPage = self.storyboard?.instantiateViewController(withIdentifier: "splashController") as! splashViewController
    
    // 遍历所有活跃场景，统一切换登录页面
    for scene in UIApplication.shared.connectedScenes {
        guard let windowScene = scene as? UIWindowScene,
              let sceneDelegate = windowScene.delegate as? SceneDelegate,
              let window = sceneDelegate.window else {
            continue
        }
        window.rootViewController = signInPage
        window.makeKeyAndVisible()
    }
}

内容的提问来源于stack exchange，提问作者Two Chains