xcode11新增SceneDelegate文件
好久之前跟新到Xcode11，跟新完成后打开以前老项目并未有什么太大变化，也就没有在意，今天新建一个项目，创建完成后，发现多了个SceneDelegate的.m和.h文件，这是什么鬼？它有什么用呢？
新创建项目目录
AppDelegate和SceneDelegate是iPadOS带来的新的多窗口支持的结果，并且有效地将应用程序委托的工作分成两部分。 原来在iOS13中，AppDelegate的文件结构发生了变化： iOS13以前：AppDelegate处理App生命周期和UI生命周期； iOS13以后：处理 App 生命周期和新的 Scene Session 生命周期，在AppDelegate.h文件中没有了window属性，而是在SceneDelegate中，可见AppDelegate不管理window而是交给SceneDelegate。
一.初始化window方法需要改变：
现在不再Appdelegate.m：
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
转交给SceneDelegate.m：
- (void)scene:(UIScene *)scene willConnectToSession:(UISceneSession *)session options:(UISceneConnectionOptions *)connectionOptions
- (void)scene:(UIScene *)scene willConnectToSession:(UISceneSession *)session options:(UISceneConnectionOptions *)connectionOptions {
UIWindowScene *windowScene = (UIWindowScene *)scene;
self.window = [[UIWindow alloc] initWithWindowScene:windowScene];
self.window.frame = windowScene.coordinateSpace.bounds;
ViewController *startVC=[[ViewController alloc]init];
UINavigationController *nav = [[UINavigationController alloc]initWithRootViewController:startVC];
self.window.rootViewController = nav;
[self.window makeKeyAndVisible];
}二.SceneDelegate适配 场景一:不需要支持多个scene，需要兼容iOS13以下，按以往的Appdelegate管理window的方式适配：
- 打开info.plist文件，删除Application Scene Manifest选项。
2.删掉SceneDelegate文件，注释以下代码：
- (UISceneConfiguration *)application:(UIApplication *)application configurationForConnectingSceneSession:(UISceneSession *)connectingSceneSession options:(UISceneConnectionOptions *)options {
// Called when a new scene session is being created.
// Use this method to select a configuration to create the new scene with.
return [[UISceneConfiguration alloc] initWithName:@"Default Configuration" sessionRole:connectingSceneSession.role];
}
- (void)application:(UIApplication *)application didDiscardSceneSessions:(NSSet<UISceneSession *> *)sceneSessions {
// 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.
}3.在AppDelegate中新增window属性，代码：
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
ViewController *startVC=[[ViewController alloc]init];
UINavigationController *nav = [[UINavigationController alloc]initWithRootViewController:startVC];
self.window.rootViewController = nav;
[self.window makeKeyAndVisible];
return YES;
}场景2: 支持多个scene，需要兼容iOS13以下：利用@available添加版本判断。 1.SceneDelegate中添加@available(iOS 13, *)； 2.AppDelegate中同样声明window属性，代码：
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
if(@available(iOS 13, *)){
}else
{
ViewController *startVC=[[ViewController alloc]init];
UINavigationController *nav = [[UINavigationController alloc]initWithRootViewController:startVC];
self.window.rootViewController = nav;
[self.window makeKeyAndVisible];
}
return YES;
}- AppDelegate两个关于Scene的方法也添加版本控制；
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