Xcode11-SceneDelegate

方案一： 如果我们不开发iPadOS多窗口APP，SceneDelegate窗口管理我们可以不需要直接删掉就好了。

1. 删除掉info.plist中Application Scene Manifest选项
2. 删除项目中的Scenedelegate.h和Scenedelegate.m
3. 删除掉APPdelegate.m中的#pragma mark - UISceneSession lifecycle代码
4. 在APPdelegate.h中添加 window属性

@property (strong, nonatomic) UIWindow * window;

方案二：使用iPadOS多窗口，且兼容iOS13以下的

// AppDelegate.h
@interface AppDelegate : UIResponder 
@property (strong, nonatomic) UIWindow *window;
@end

//AppDelegate.m
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    if (@available(iOS 13, *)) {
        return YES;
    } else {
        [self olderSettingFunc];
        return YES;
    }
    return YES;
    
}
//iOS13以前的设置方法
- (void)olderSettingFunc {
    //设置跟视图控制器
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.window.backgroundColor = [UIColor whiteColor];
    self.window.rootViewController = [[MainTabBarController alloc] init];
    [self.window makeKeyAndVisible];
            
}

//SceneDelegate.m
//程序完成启动,和didFinishLaunchingWithOptions相似
- (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).
    
    //设置跟视图控制器
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.window.windowScene = (UIWindowScene *)scene;//Xcode11以后,设置跟视图,要在SceneDelegate中添加这段代码
    self.window.backgroundColor = [UIColor whiteColor];
    self.window.rootViewController = [[MainTabBarController alloc] init];
    [self.window makeKeyAndVisible];
}