Mac Catalyst、iOS13

场景只有iPad和macOS下才可用，场景可以理解为窗口（这时候UIWindow将理解为UIView++），一个场景（窗口）对应一个Scene Delegate对象，建议每个Scene Delegate类对应一个UIViewController

默认的info.plist配置（如不需要多场景，建议删除此配置，应用程序的生命周期将变为由AppDelegate管理）

MacCatalyst - Default info plist.png

Enable Multiple Windows：如果需要多场景（窗口），需要把此值设为YES，否则无法使用多场景
Configuration Name：配置名，可理解为场景的标识符（必填项）
Delegate Class Name：场景对应的代理对象类，每新建一个场景，都会创建一个新的代理对象（必填项）
Storyboard Name：场景将自动生成此Storyboard里的Initial View Controller（默认视图控制器），如不设置，则需要在Scene Delegate里创建UIWindow和UIViewController对象（选填项）
Class Name：自定义UIScene子类，默认为UIWindowScene，一般不需要更改（选填项）

多场景配置

MacCatalyst - Custom info plist.png

UIApplicationSceneManifest

    UIApplicationSupportsMultipleScenes
    
    UISceneConfigurations
    
        UIWindowSceneSessionRoleApplication
        
            
                UISceneConfigurationName
                Default Configuration
                UISceneDelegateClassName
                SceneDelegate
                UISceneStoryboardFile
                Main
            
            
                UISceneConfigurationName
                Other Configuration
                UISceneDelegateClassName
                OtherSceneDelegate
                UISceneStoryboardFile
                Other

AppDelegate.m 修改

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // 兼容iOS13之前版本
    if (@available(iOS 13.0, *)) { } else {
        UIStoryboard *storyboard            = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
        UIViewController *viewController    = [storyboard instantiateInitialViewController];
        self.window.rootViewController      = viewController;
    }
    return YES;
}

- (UISceneConfiguration *)application:(UIApplication *)application configurationForConnectingSceneSession:(UISceneSession *)connectingSceneSession options:(UISceneConnectionOptions *)options API_AVAILABLE(ios(13.0)) {
    // 应用程序正常退出/全部的窗口被正常关闭后再启动才会进入此方法
    NSUserActivity *userActivity    = options.userActivities.anyObject;
    NSString *activityType          = userActivity.activityType;
    UISceneSessionRole role         = connectingSceneSession.role;
    // 假如activityType为空，表示是刚启动的，否则是新创建的场景
    if (activityType == nil) {
        activityType                = @"Default Configuration";
        role                        = UIWindowSceneSessionRoleApplication;
    }
    return [[UISceneConfiguration alloc] initWithName:activityType sessionRole:role];
}

OtherSceneDelegate.h 需要遵循协议（OtherSceneDelegate.m的内容和SceneDelegate.m一样）

#import 
@interface OtherSceneDelegate : UIResponder 
@property (strong, nonatomic) UIWindow * window;
@end

Other.storyboard 新增一个视图控制器并设置Is Initial View Controller

MacCatalyst - Initial view controller.png

创建（激活）场景

NSUserActivity *userActivity    = [[NSUserActivity alloc] initWithActivityType:@"Other Configuration"];
UIApplication *app              = [UIApplication sharedApplication];
[app requestSceneSessionActivation:nil
                      userActivity:userActivity
                           options:nil
                      errorHandler:nil];

(Show Other Scene为按钮，点击后执行上面的代码显示右边的窗口)

macOS下效果：

MacCatalyst - Show scene.png

iPadOS下效果：

MacCatalyst - Show scene iPad.png

关闭场景（例如在UIViewController实例里）

UIApplication *app = [UIApplication sharedApplication];
[app requestSceneSessionDestruction:self.view.window.windowScene.session
                            options:nil
                       errorHandler:nil];

激活（前置）已有的场景

UIApplication *app      = [UIApplication sharedApplication];
NSArray *openSessions   = app.openSessions.allObjects;
for (UISceneSession *session in openSessions) {
    if ([session.configuration.name isEqualToString:@"Other Configuration"]) {
        [app requestSceneSessionActivation:session
                              userActivity:nil
                                   options:nil
                              errorHandler:nil];
    }
}

假如info.plist的场景配置不设置Storyboard Name，则需要自行创建窗口和视图控制器

// OtherSceneDelegate.m

- (void)scene:(UIScene *)scene willConnectToSession:(UISceneSession *)session options:(UISceneConnectionOptions *)connectionOptions API_AVAILABLE(ios(13.0)) {
    UIStoryboard *storyboard            = [UIStoryboard storyboardWithName:@"Other" bundle:nil];
    UIViewController *viewController    = [storyboard instantiateInitialViewController];
    UIWindowScene *windowScene          = (UIWindowScene *)scene;
    UIWindow *window                    = [[UIWindow alloc] initWithWindowScene:windowScene];
    self.window                         = window;
    window.rootViewController           = viewController;
    [window makeKeyAndVisible];
}

恢复场景

场景（窗口）在程序意外退出后，重启时会调用Scene Delegate里的 - (void)scene:(UIScene *)scene willConnectToSession:(UISceneSession *)session options:(UISceneConnectionOptions *)connectionOptions 方法以重新连接（恢复）场景，每一个场景都有一个唯一标识符(session.persistentIdentifier)，假如遇到意外退出恢复时会带上旧的标识符，可通过使用此标识符保存或读取数据

macOS上运行的问题

窗口全部关闭后点击程序坞（Dock）上的图标，控制台会出现警告或应用程序Crash

*** Assertion failure in -[UINSApplicationDelegate applicationShouldHandleReopen:hasVisibleWindows:], /AppleInternal/BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKitCore/UIKit-3920.40.401/UIKitMacHelper/App/UINSApplicationDelegate.m:886

[xpc.exceptions] connection to service on pid 6151 named com.apple.uikitsystemapp.services: Exception caught during invocation of reply block to message 'createNewSceneOfSize:background:persistenceIdentifier:completionHandler:'.

Ignored Exception: -[UINSApplicationDelegate applicationShouldHandleReopen:hasVisibleWindows:]_block_invoke: _createNewForegroundSceneWithCompletionHandler Completion handler arrived off the main thread.

解决方法：通过添加AppKit插件解决，详情请参阅《Mac Catalyst - macOS AppKit 插件》

生命周期

-[AppDelegate application:didFinishLaunchingWithOptions:]
-[AppDelegate application:configurationForConnectingSceneSession:options:] 
-[SceneDelegate scene:willConnectToSession:options:]
-[SceneDelegate sceneWillEnterForeground:]
-[SceneDelegate sceneDidBecomeActive:]

// 关闭后...
-[SceneDelegate sceneWillResignActive:]
-[SceneDelegate sceneDidEnterBackground:]
-[SceneDelegate sceneDidDisconnect:]
-[AppDelegate application:didDiscardSceneSessions:]

Mac Catalyst、iOS13 - UIScene