iOS 模拟器在尝试创建框架时显示空白屏幕

Question

在 Big Nerd Ranch：iOS 编程第 4 版 教科书的第 4 章中，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：

我不确定为什么会这样。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。

这是 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

Answer 1

如果你使用应用程序场景，你在应用程序委托中手动创建的窗口将被忽略（准确地说它在很短的时间内保持关键窗口，直到场景使自己的窗口成为关键窗口）。所以你要么应该附加你在场景委托的

-[UISceneDelegate scene:willConnectToSession:options:]

方法中创建的窗口：

- (void)scene:(UIScene *)scene willConnectToSession:(UISceneSession *)session options:(UISceneConnectionOptions *)connectionOptions {
    UIWindow *window = [[UIWindow alloc] initWithWindowScene:(UIWindowScene *)scene];

    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(160, 240, 100, 150)];
    view.backgroundColor = UIColor.redColor;
    [window addSubview:view];

    window.backgroundColor = UIColor.whiteColor;
    [window makeKeyAndVisible];
    self.window = window;
}

.. 或者在您的应用程序中删除场景委托（您可以参考 这个问题 下的讨论以获取有关如何执行此操作的更多详细信息）并使其与旧的良好应用程序委托窗口一起使用。请注意，在这种情况下，如果没有指定

rootViewController

，您将无法使用窗口，因此您至少需要设置一个虚拟控制器：

_window.rootViewController = [UIViewController new];