The app delegate must implement the window property

新建Xcode项目报错：

[Application] The app delegate must implement the window property if it wants to use a main storyboard file.

只需要在 AppDelegate.h 文件中加入 window 属性即可。

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (nonatomic, strong) UIWindow *window;

@end