iOS13 AppDelegate、SceneDelegate兼

如果不适配就会导致iOS13以前的系统无法正确加载UIWindow而导致APP黑屏问题，如下是保留SceneDelegate且兼容iOS13以前系统的方法

AppDelegate.h

#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>

/// 兼容iOS13之前的版本
@property (strong, nonatomic) UIWindow *window;

@end

AppDelegate.m

#import "AppDelegate.h"

@interface AppDelegate ()

@end

@implementation AppDelegate


- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    
    if (@available(iOS 13.0, *))
    {
        // 在SceneDelegate里创建UIWindow
    }
    else
    {
        self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
        [self.window setBackgroundColor:[UIColor whiteColor]];
        
        NSString *mainStoryboardFileName    =
        [[NSBundle mainBundle].infoDictionary valueForKey:@"UIMainStoryboardFile"];
        
        UIStoryboard *mainStoryboard        =
        [UIStoryboard storyboardWithName:mainStoryboardFileName
                                  bundle:[NSBundle mainBundle]];
        
        [self.window setRootViewController:[mainStoryboard instantiateInitialViewController]];
        [self.window makeKeyAndVisible];
    }
    return YES;
}

#pragma mark - 兼容iOS13之前的版本
- (void)applicationWillResignActive:(UIApplication *)application
{
    
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    
    
}

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    
}

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    
    
}

- (void)applicationWillTerminate:(UIApplication *)application
{
    
    
}

#pragma mark - iOS13 以后 UISceneSession lifecycle
- (UISceneConfiguration *)application:(UIApplication *)application configurationForConnectingSceneSession:(UISceneSession *)connectingSceneSession options:(UISceneConnectionOptions *)options  API_AVAILABLE(ios(13.0)){
    // 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  API_AVAILABLE(ios(13.0)){
    // 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.
}

@end

SceneDelegate.h

#import <UIKit/UIKit.h>

@interface SceneDelegate : UIResponder <UIWindowSceneDelegate>

@property (strong, nonatomic) UIWindow * window;

@end

SceneDelegate.m

#import "SceneDelegate.h"

@interface SceneDelegate ()

@end

@implementation SceneDelegate


- (void)scene:(UIScene *)scene willConnectToSession:(UISceneSession *)session options:(UISceneConnectionOptions *)connectionOptions  API_AVAILABLE(ios(13.0)){
    // 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).
    
    /*
    // 在这里手动创建新的window
    if (@available(iOS 13.0, *))
    {
        UIWindowScene *windowScene = (UIWindowScene *)scene;
        self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
        [self.window setWindowScene:windowScene];
        [self.window setBackgroundColor:[UIColor systemBackgroundColor]];
        
        NSString *mainStoryboardFileName    =
        [[NSBundle mainBundle].infoDictionary valueForKey:@"UIMainStoryboardFile"];
        
        UIStoryboard *mainStoryboard        =
        [UIStoryboard storyboardWithName:mainStoryboardFileName
                                  bundle:[NSBundle mainBundle]];
        
        [self.window setRootViewController:[mainStoryboard instantiateInitialViewController]];
        [self.window makeKeyAndVisible];
    }
    else
    {
        // 在AppDelegate里创建UIWindow
    }
     */
}


- (void)sceneDidDisconnect:(UIScene *)scene  API_AVAILABLE(ios(13.0)){
    // Called as the scene is being released by the system.
    // This occurs shortly after the scene enters the background, or when its session is discarded.
    // Release any resources associated with this scene that can be re-created the next time the scene connects.
    // The scene may re-connect later, as its session was not neccessarily discarded (see `application:didDiscardSceneSessions` instead).
}


- (void)sceneDidBecomeActive:(UIScene *)scene  API_AVAILABLE(ios(13.0)){
    // Called when the scene has moved from an inactive state to an active state.
    // Use this method to restart any tasks that were paused (or not yet started) when the scene was inactive.
}


- (void)sceneWillResignActive:(UIScene *)scene  API_AVAILABLE(ios(13.0)){
    // Called when the scene will move from an active state to an inactive state.
    // This may occur due to temporary interruptions (ex. an incoming phone call).
}


- (void)sceneWillEnterForeground:(UIScene *)scene  API_AVAILABLE(ios(13.0)){
    // Called as the scene transitions from the background to the foreground.
    // Use this method to undo the changes made on entering the background.
}


- (void)sceneDidEnterBackground:(UIScene *)scene  API_AVAILABLE(ios(13.0)){
    // Called as the scene transitions from the foreground to the background.
    // Use this method to save data, release shared resources, and store enough scene-specific state information
    // to restore the scene back to its current state.
}


@end