1.在xcode11 beta上创建新项目,默认版本控制是iOS13,当设置为小于该版本后,会发现低版本手机打开是黑屏

发现iOS13初始文件多了SceneDelegate这个类,而iOS13以前由AppDelegate处理的部分逻辑改由SceneDelegate去处理了,而低版本手机不能正确处理,所以造成黑屏

SceneDelegate.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 {
    // 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).
}


- (void)sceneDidDisconnect:(UIScene *)scene {
    // 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 {
    // 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 {
    // 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 {
    // 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 {
    // 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

此时的AppDelegate内容如下

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@end

我们只需将window属性添加回去即可,修改后如下

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@end

这时运行应该ok了