在 UINavigationController 中第一次运行时推送视图

Question

我在我的应用程序中实现了UINavigationController，我想要实现的是以编程方式确定该应用程序是否已启动。我需要这个来确定应该向用户显示哪个视图。如果这是第一次运行，我需要显示与其他任何时候不同的视图。

当我不使用 UINavigationController 时很容易，但在这种情况下，当我使用我的方法时，我将摆脱 UINavigationController 层次结构。

这是我用来确定首次运行的方法：

+ (void)executeBlockAtTheFirstRun:(void (^)())firstRunBlock atAnotherRun:(void (^)())anotherRunBlock
{
    // Checking whether HasAlreadyBeenLaunched key is set to be YES
    if ([[NSUserDefaults standardUserDefaults] boolForKey:@"HasAlreadyBeenLaunched"]) {
        // Running block given by the user when this isn't the first run of the app
        anotherRunBlock();

        // Uncomment this if you want the log
        //NSLog(@"Application has already been launched");
    } else {
        // Seeting the bool value for key HasAlreadyBeenLaunched and synchronising user defaults
        [[NSUserDefaults standardUserDefaults] setBool:YES forKey:@"HasAlreadyBeenLaunched"];
        [[NSUserDefaults standardUserDefaults] synchronize];

        // Running the block with code provided by the user for the first run of the app
        firstRunBlock();

        // Uncommeent this f you want the log
        // NSLog(@"This is the first run");
    }
}

所以当我放入完成块时：

NSString *storyboardID = [self hasEverBeenLaunched]? @"MainView" : @"LoginView";

self.window.rootViewController = [self.window.rootViewController.storyboard instantiateViewControllerWithIdentifier:storyboardID];

并将所有内容放入 AppDelegate.m 我可以管理视图，但正如我所说，我的 UINavigationController 层次结构消失了。我应该怎么做才能让一切正常运行？

Answer 1

如果您想要导航控制器，请制作导航控制器！而不是

self.window.rootViewController = 
    [self.window.rootViewController.storyboard    
        instantiateViewControllerWithIdentifier:storyboardID];

说

UIViewController* root =         
    [self.window.rootViewController.storyboard    
        instantiateViewControllerWithIdentifier:storyboardID];
UINavigationController* nav = 
    [UINavigationController alloc] initWithRootViewController: root];
self.window.rootViewController = nav;

Answer 2

在storyboard 中直观地将您的根视图控制器设置为UINavigationController。
试试下面的方法：

if ([[NSUserDefaults standardUserDefaults] boolForKey:@"HasAlreadyBeenLaunched"]) {

MainViewController *mainViewController = [[UIStoryboard storyboardWithName:@"Main" bundle:[NSBundle mainBundle]] instantiateViewControllerWithIdentifier:@"MainViewController"];

    [self.navigationController setViewControllers:[NSArray arrayWithObject:mainViewController] animated:YES];

    } else {

LoginViewController *loginViewController = [[UIStoryboard storyboardWithName:@"Main" bundle:[NSBundle mainBundle]] instantiateViewControllerWithIdentifier:@"loginViewController"];

    [self.navigationController setViewControllers:[NSArray arrayWithObject:loginViewController] animated:YES];

    } 

或者你可以像@matt 回答描述的那样直接设置你的根视图控制器。

Answer 3

您必须先创建一个导航控制器并设置为根视图控制器：

NSString *storyboardID = [self hasEverBeenLaunched]? @"MainView" : @"LoginView";
UIViewController *vc = [self.window.rootViewController.storyboard instantiateViewControllerWithIdentifier:storyboardID];

UINavigationController *nc = [[UINavigationController alloc] initWithRootViewController:vc];
self.window.rootViewController = nc;
[self.window makeKeyAndVisible];

Answer 4

在情节提要中从 MainViewController segue 中创建名称为“ShowLoginView”的推送 LoginViewController。和代码：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    if (!self.hasEverBeenLaunched) dispatch_async(dispatch_get_main_queue(), ^(){
       [[(UINavigationController*)self.window.rootViewController visibleViewController] performSegueWithIdentifier:@"ShowLoginView" sender:nil];
    });
    return YES;
}