self.navigationController为null [英] self.navigationController is null

问题描述

在我的viewcontroller中，我有一个按钮，按下按钮，输入navigationController，我的代码如下：

in my viewcontroller,I have a button,when press the button,entry the navigationController,my code like:

-(IBAction)ShangHaiButtonPressed:(id)sender{
    marketviewcontroller = [[MarketViewController alloc]initWithNibName:@"MarketViewController" bundle:nil];
    NSLog(@"%@",self.navigationController);
    [self.navigationController pushViewController:marketviewcontroller animated:YES];
    [marketviewcontroller release];   
}

但我可以看到self.navigationController为null，如何解决这个问题？谢谢。

but I can see the self.navigationController is null,how to solve this problem?thank you.

更新：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    _switchviewcontroller = [[SwitchViewController alloc]initWithNibName:@"SwitchViewController" bundle:nil];
    [self.window addSubview:_switchviewcontroller.view];
    [self.window makeKeyAndVisible];
    return YES;
}

推荐答案

navigationController <仅当视图控制器位于导航控制器的导航堆栈中时，视图控制器的/ em>属性才会返回有效的导航控制器对象。可以通过以下方式将视图控制器添加到导航堆栈。

The navigationController property of a view controller will return a valid navigation controller object only if the view controller is in a navigation controller's navigation stack. A view controller can be added to a navigation stack in the following ways.

1. 使用 initWithRootViewController：方法将视图控制器作为导航控制器的rootViewController > UINavigationController

1. By making the view controller the rootViewController of a navigation controller using initWithRootViewController: method of UINavigationController

使用 UINavigationController 的 pushViewController：方法推送视图控制器。

By pushing the view controller using pushViewController: method of UINavigationController.

确保以上述任何方式将视图控制器添加到导航堆栈。

Make sure your view controller is added to the navigation stack in any of the above ways.

编辑：（在didFinishLaunchingWithOptions：代码添加到问题后）：

(After the didFinishLaunchingWithOptions: code added to the question):

将 didFinishLaunchingWithOptions：方法更改为此，

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    _switchviewcontroller = [[SwitchViewController alloc]initWithNibName:@"SwitchViewController" bundle:nil];
    UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:_switchviewcontroller];
    [self.window addSubview:navController.view];
    [navController release];
    [self.window makeKeyAndVisible];
    return YES;
}

Swift 4（版本）：

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey : Any]? = nil) -> Bool {
    switchviewcontroller = SwitchViewController(nibName: "SwitchViewController", bundle: nil)
    let navController = UINavigationController(rootViewController: switchviewcontroller)
    window.addSubview(navController.view)
    window.makeKeyAndVisible()
    return true
}

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