第四章大宅男牧场：iOS编程第4版教科书中，我们应该在AppDelegate.m**文件的视图中间创建一个红色矩形，并将其显示在模拟器中。
我已经逐字复制了代码，当我运行模拟器时，我得到一个像这样的空白屏幕：

我不知道为什么会这样。我已经将window的属性放在AppDelegate.h文件中，所以我知道这不是原因。
以下是AppDelegate.m文件中的代码：

//
//  AppDelegate.m
//  Hypnosister
//
//
//

#import "AppDelegate.h"
#import "BNRHypnosisView.h"

@interface AppDelegate ()

@end

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    CGRect firstFrame = CGRectMake(160, 240, 100, 150);
    
    BNRHypnosisView *firstView = [[BNRHypnosisView alloc]initWithFrame:firstFrame];
    firstView.backgroundColor = [UIColor redColor];
    [self.window addSubview:firstView];
    
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}

#pragma mark - UISceneSession lifecycle

- (UISceneConfiguration *)application:(UIApplication *)application configurationForConnectingSceneSession:(UISceneSession *)connectingSceneSession options:(UISceneConnectionOptions *)options {
    // 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 {
    // 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