使用UISceneDelegate将旧的Xcode项目迁移到新的项目 编辑1：原始答案：步骤1：在Info.plist中添加场景清单步骤2：创建包含以下内容的SceneDelegate.swift文件步骤3：更新AppDelegate

问题描述

我有一个旧的Xcode项目，没有UISceneDelegate方法。是否可以使用UISceneDelegate方法将旧的Xcode项目迁移到新的项目，但仍保持与iOS 12的兼容性？

如果是，怎么办？因为我在iOS 14中看到了很多错误，所以唯一的解决方法是使用UISceneDelegate方法。

解决方法

编辑1：

在呈现View Controller的视图之后，请确保查询windowOrientation。通常在viewDidLoad()和viewWillAppear(_:)中，view.window是nil，请选中此answer。只需检查windowOrientation中viewDidAppear(_:)的值即可。

如果您在尝试使用以下定义之前仍遇到访问此值的问题

private var windowOrientation: UIInterfaceOrientation {
    if #available(iOS 13.0,*) {
        return UIApplication.shared.windows.first?.windowScene?.interfaceOrientation ?? .unknown
    } else {
        // Fallback on earlier versions
        return UIApplication.shared.statusBarOrientation
    }
}

我不确定您的应用程序是否使用多个窗口，但是不确定是否只有一个（由于您没有以编程方式创建任何窗口），因此以下定义应该可以正常工作。

var hasTopNotch: Bool {
    return UIApplication.shared.windows.first?.safeAreaInsets.top ?? 0 > 20
}

原始答案：

UISceneDelegate已在iOS 13.0中引入，因此无法与iOS 12兼容，您需要完全依赖UIApplicationDelegate。要为UISceneDelegate支持iOS 13.x，您需要添加显式可用性检查以避免编译错误。

步骤1：在Info.plist中添加场景清单

以Info.plist的身份打开Source Code并添加以下内容

<key>UIApplicationSceneManifest</key>
<dict>
    <key>UIApplicationSupportsMultipleScenes</key>
    <false/>
    <key>UISceneConfigurations</key>
    <dict>
        <key>UIWindowSceneSessionRoleApplication</key>
        <array>
            <dict>
                <key>UISceneConfigurationName</key>
                <string>Default Configuration</string>
                <key>UISceneDelegateClassName</key>
                <string>$(PRODUCT_MODULE_NAME).SceneDelegate</string>
                <key>UISceneStoryboardFile</key>
                <string>Main</string>
            </dict>
        </array>
    </dict>
</dict>

步骤2：创建包含以下内容的SceneDelegate.swift文件

import UIKit
@available(iOS 13.0,*)
class SceneDelegate: UIResponder,UIWindowSceneDelegate {

    var window: UIWindow?


    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 }
    }

    func sceneDidDisconnect(_ scene: UIScene) {
        // Called as the scene is being released by the system.
        // This occurs shortly after the scene enters the background,or when its session is discarded.
        // Release any resources associated with this scene that can be re-created the next time the scene connects.
        // The scene may re-connect later,as its session was not neccessarily discarded (see `application:didDiscardSceneSessions` instead).
    }

    func sceneDidBecomeActive(_ scene: UIScene) {
        // Called when the scene has moved from an inactive state to an active state.
        // Use this method to restart any tasks that were paused (or not yet started) when the scene was inactive.
    }

    func sceneWillResignActive(_ scene: UIScene) {
        // Called when the scene will move from an active state to an inactive state.
        // This may occur due to temporary interruptions (ex. an incoming phone call).
    }

    func sceneWillEnterForeground(_ scene: UIScene) {
        // Called as the scene transitions from the background to the foreground.
        // Use this method to undo the changes made on entering the background.
    }

    func sceneDidEnterBackground(_ scene: UIScene) {
        // Called as the scene transitions from the foreground to the background.
        // Use this method to save data,release shared resources,and store enough scene-specific state information
        // to restore the scene back to its current state.
    }


}

步骤3：更新AppDelegate

1. 添加 UISceneSession Lifecycle个方法。

// MARK: UISceneSession Lifecycle
@available(iOS 13.0,*)
func application(_ application: UIApplication,configurationForConnecting connectingSceneSession: UISceneSession,options: UIScene.ConnectionOptions) -> UISceneConfiguration {
    // Called when a new scene session is being created.
    // Use this method to select a configuration to create the new scene with.
    return UISceneConfiguration(name: "Default Configuration",sessionRole: connectingSceneSession.role)
}
@available(iOS 13.0,didDiscardSceneSessions sceneSessions: Set<UISceneSession>) {
    // Called when the user discards a scene session.
    // If any sessions were discarded while the application was not running,this will be called shortly after application:didFinishLaunchingWithOptions.
    // Use this method to release any resources that were specific to the discarded scenes,as they will not return.
}

ii）最后参考Apple Documentation。您可以参考https://dev.to/kevinmaarek/add-a-scene-delegate-to-your-current-project-5on了解其他清理和设置任务。