在启动时在视图控制器上显示模态视图控制器

Question

在我的AppDelegate.m 中，我有以下代码在启动时为用户设置初始视图控制器，具体取决于钥匙串中是否存储了凭据。

如果用户确实存储了凭据，则应用程序将使用故事板 ID balancescreen 实例化主用户界面。这适用于下面的代码。

如果用户没有存储凭据，我想在 balancescreen 的顶部显示带有情节提要 ID loginscreen 的登录视图控制器，modally。 strong> 当输入正确的凭据时，视图控制器将被关闭（我已经处理过这个），用户显示主界面。 这就是我需要帮助的地方，找到解决方案来做到这一点而不会出现应用程序故障。

这是我目前拥有的代码：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    // grabs password for the only account
    // (there shall always only be one set of credentials stored so this will work)

    NSString *password = [SSKeychain passwordForService:@"MyOpal" account:[[SSKeychain accountsForService:@"MyOpal"][0] valueForKey:@"acct"]];


    // if password has a length (aka user has previously used the application with credentials in keychain), direct to the app
    // if password has no length (aka does not exist because user has not used the application before), direct to login screen

    if (password.length > 0) {

        self.window = [[UIWindow alloc] initWithFrame:UIScreen.mainScreen.bounds];
        UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
        UIViewController *viewController = [storyboard instantiateViewControllerWithIdentifier:@"balancescreen"];

        self.window.rootViewController = viewController;
        [self.window makeKeyAndVisible];


    } else {

        // do something here to present login view controller modally over the top of the main interface (with storyboard id, 'balance screen')
        // therefore, when the user logs in, the login view controller will dismiss, with the user greeted at the main interface


    }

    return YES;
}

编辑：这是我的故事板设置：

Answer 1

不要更改应用程序中的 rootViewController。使 rootViewController 接收导航到登录或应用程序的请求。

更改窗口的 rootViewController 是不好的做法，因为您需要手动执行动画。故事板流程如下所示：

Answer 2

试试这个：

if (password.length > 0) {

    self.window = [[UIWindow alloc] initWithFrame:UIScreen.mainScreen.bounds];
    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
    UIViewController *viewController = [storyboard instantiateViewControllerWithIdentifier:@"balancescreen"];

    self.window.rootViewController = viewController;
    [self.window makeKeyAndVisible];


} else {

    // go on as before
    self.window = [[UIWindow alloc] initWithFrame:UIScreen.mainScreen.bounds];
    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
    UIViewController *viewController = [storyboard instantiateViewControllerWithIdentifier:@"balancescreen"];

    // instantiate the LoginViewController
    LoginViewController *loginViewController = [storyboard instantiateViewControllerWithIdentifier:@"LoginViewController"];

    self.window.rootViewController = viewController;
    [self.window makeKeyAndVisible];

    // present the LoginViewController modoally with viewController as presenter
    [viewController presentViewController:loginViewController animated:NO completion:nil];

}

显然，我假设您处理登录的UIViewController 称为LoginViewController。如果不是这种情况，请继续在您的代码中调整其名称:)

无论如何，对于这种情况，我宁愿建议您不要以模态方式显示登录。更好的方法是实际更改应用程序主 UIWindow 的 rootViewController 属性。

在你的情况下可能看起来像这样：

    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];

    if (password.length > 0) {
       UIViewController *viewController = [storyboard instantiateViewControllerWithIdentifier:@"balancescreen"];
       self.window.rootViewController = viewController;
    } 
    else {
       LoginViewController *loginViewController = [storyboard instantiateViewControllerWithIdentifier:@"LoginViewController"];
       self.window.rootViewController = loginViewController;
    }
    [self.window makeKeyAndVisible];