iOS13新增SceneDelegate初始化view

iOS13里APP启动稍作调整。AppDelegate的职责发现了改变：在iOS13之前，AppDelegate的负责处理App生命周期和UI生命周期。iOS13之后，AppDelegate只负责处理App生命周期，新增SceneDelegate负责处理Scene Session生命周期和UI的生命周期。即AppDelegate不再负责UI生命周期，所有UI生命周期交给SceneDelegate处理。

第一步：xcode11创建工程后，删除默认Main.storyboard文件。

第二步：工程配置【General】中清空Main Interface，不再采用Main.storyboard

第三步：Info.plist中, 删除SceneDelegate的StoryboardName

第四步：在SceneDelegate.m文件中willConnectToSession回调中初始化View

- (void)scene:(UIScene *)scene willConnectToSession:(UISceneSession *)session options:(UISceneConnectionOptions *)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).
    UIWindowScene *windowScene = (UIWindowScene *)scene;
    self.window = [[UIWindow alloc] initWithWindowScene:windowScene];
    self.window.backgroundColor = [UIColor purpleColor];
    UIViewController *VC = [[UIViewController alloc]init];
    UINavigationController *NVC = [[UINavigationController alloc]initWithRootViewController:VC];
    [self.window setRootViewController:NVC];
    [self.window makeKeyAndVisible];
}