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）
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
<key>UIApplicationSceneManifest</key>
<dict>
<key>UIApplicationSupportsMultipleScenes</key>
<true/>
<key>UISceneConfigurations</key>
<dict>
<key>UIWindowSceneSessionRoleApplication</key>
<array>
<dict>
<key>UISceneConfigurationName</key>
<string>Default Configuration</string>
<key>UISceneDelegateClassName</key>
<string>SceneDelegate</string>
<key>UISceneStoryboardFile</key>
<string>Main</string>
</dict>
<dict>
<key>UISceneConfigurationName</key>
<string>Other Configuration</string>
<key>UISceneDelegateClassName</key>
<string>OtherSceneDelegate</string>
<key>UISceneStoryboardFile</key>
<string>Other</string>
</dict>
</array>
</dict>
</dict>
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<UIWindowSceneDelegate>协议（OtherSceneDelegate.m的内容和SceneDelegate.m一样）
#import <UIKit/UIKit.h>
@interface OtherSceneDelegate : UIResponder <UIWindowSceneDelegate>
@property (strong, nonatomic) UIWindow * window;
@end
Other.storyboard 新增一个视图控制器并设置Is Initial View Controller
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：
iPadOS下效果：
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] <NSXPCConnection: 0x60000300c7e0> 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:]
