C# Xamarin iOS NavigationController返回null

我仍在学习Xamarin ios的诀窍，并基于以下示例实现了一个侧抽屉。在本教程中，有一个主视图控制器类，该类随后分配一个主导航控制器和一个侧菜单

抽屉菜单选项被输入菜单类，“主屏幕/第一个屏幕”被传递到主导航控制器类，主导航控制器类是UINavigationController类的子类

我的主屏幕是一个tabcontroller类，我试图引用该类中的导航控制器，但它总是返回null

以下是我面临的两大挑战：

• 选项卡控制器和单选项卡视图控制器中的导航控制器始终为空
• 导航栏上不显示我的各个选项卡控制器类的标题

下面是AppDelegate类的

[Register ("AppDelegate")]
public class AppDelegate : UIApplicationDelegate
{
        public SlideoutNavigationController Menu { get; private set; }

 public override bool FinishedLaunching (UIApplication application, NSDictionary launchOptions)
    {
                Menu = new SlideoutNavigationController ();

 var tabBarController = GetViewController (Main, "MainTabBarController");

                Menu.MainViewController = new MainNavigationController (tabBarController, Menu);
                Menu.MenuViewController = new MenuNavigationController (new MenuControllerLeft (), Menu) { NavigationBarHidden = true };
                SetRootViewController (Menu, false);

        return true;
    }
}

主选项卡控制器类

 public partial class MainTabBarController : UITabBarController
{
        UINavigationItem titleRequest,titleHome,titleSell;

  public MainTabBarController (IntPtr handle) : base (handle)
    {
  //Create an instance of our AppDelegate
         appDelegate = UIApplication.SharedApplication.Delegate as AppDelegate;

        //Get an instance of our Main.Storyboard
        var mainStoryboard = appDelegate.Main;

        var tab1 = appDelegate.GetViewController (mainStoryboard, "Tab1");

        var tab2 = appDelegate.GetViewController (mainStoryboard, "Tab2");

        var tab3 = appDelegate.GetViewController (mainStoryboard, "Tab3");


        var tabs = new UIViewController[] {
            tab1, tab2, tab3
        };

        this.SelectedIndex = 1;
        ViewControllers = tabs;
  }

  public override void ViewDidLoad ()
    {
        base.ViewDidLoad ();


            if(this.SelectedIndex == 0)
            {

                titleRequest = new UINavigationItem ("TAB 1");
                this.NavigationController.NavigationBar.PushNavigationItem (titleRequest, true); // NavigationController here is null

            }else if(this.SelectedIndex == 1)
            {
                titleHome = new UINavigationItem ("TAB 2");
                this.NavigationController.NavigationBar.PushNavigationItem (titleHome, true);


            }else{

                titleSell = new UINavigationItem ("TAB 3");
                this.NavigationController.NavigationBar.PushNavigationItem (titleSell, true);
            }

  }
 }

 public class MainNavigationController : UINavigationController
{

 public MainNavigationController(UIViewController rootViewController, SlideoutNavigationController slideoutNavigationController)
        : this(rootViewController, slideoutNavigationController, 

            new UIBarButtonItem(UIImage.FromBundle("icon_sidemenu.png"), UIBarButtonItemStyle.Plain, (s, e) => {}))
    {
    }
  public MainNavigationController(UIViewController rootViewController, SlideoutNavigationController slideoutNavigationController, UIBarButtonItem openMenuButton)
        : base(rootViewController)
    {
        openMenuButton.Clicked += (s, e) => slideoutNavigationController.Open(true);
        rootViewController.NavigationItem.LeftBarButtonItem = openMenuButton;
    }

   public override void ViewDidLoad()
    {
        base.ViewDidLoad();
        this.Delegate = new NavigationControllerDelegate();
        InteractivePopGestureRecognizer.Enabled = true;

    }
   public override void PushViewController(UIViewController viewController, bool animated)
    {
        // To avoid corruption of the navigation stack during animations disabled the pop gesture
        if (InteractivePopGestureRecognizer != null)
            InteractivePopGestureRecognizer.Enabled = false;
        base.PushViewController(viewController, animated);
    }

    private class NavigationControllerDelegate : UINavigationControllerDelegate
    {
        public override void DidShowViewController(UINavigationController navigationController, UIViewController viewController, bool animated)
        {
            // Enable the gesture after the view has been shown
            navigationController.InteractivePopGestureRecognizer.Enabled = true;
        }
    }
}

主导航控制器类

 public partial class MainTabBarController : UITabBarController
{
        UINavigationItem titleRequest,titleHome,titleSell;

  public MainTabBarController (IntPtr handle) : base (handle)
    {
  //Create an instance of our AppDelegate
         appDelegate = UIApplication.SharedApplication.Delegate as AppDelegate;

        //Get an instance of our Main.Storyboard
        var mainStoryboard = appDelegate.Main;

        var tab1 = appDelegate.GetViewController (mainStoryboard, "Tab1");

        var tab2 = appDelegate.GetViewController (mainStoryboard, "Tab2");

        var tab3 = appDelegate.GetViewController (mainStoryboard, "Tab3");


        var tabs = new UIViewController[] {
            tab1, tab2, tab3
        };

        this.SelectedIndex = 1;
        ViewControllers = tabs;
  }

  public override void ViewDidLoad ()
    {
        base.ViewDidLoad ();


            if(this.SelectedIndex == 0)
            {

                titleRequest = new UINavigationItem ("TAB 1");
                this.NavigationController.NavigationBar.PushNavigationItem (titleRequest, true); // NavigationController here is null

            }else if(this.SelectedIndex == 1)
            {
                titleHome = new UINavigationItem ("TAB 2");
                this.NavigationController.NavigationBar.PushNavigationItem (titleHome, true);


            }else{

                titleSell = new UINavigationItem ("TAB 3");
                this.NavigationController.NavigationBar.PushNavigationItem (titleSell, true);
            }

  }
 }

 public class MainNavigationController : UINavigationController
{

 public MainNavigationController(UIViewController rootViewController, SlideoutNavigationController slideoutNavigationController)
        : this(rootViewController, slideoutNavigationController, 

            new UIBarButtonItem(UIImage.FromBundle("icon_sidemenu.png"), UIBarButtonItemStyle.Plain, (s, e) => {}))
    {
    }
  public MainNavigationController(UIViewController rootViewController, SlideoutNavigationController slideoutNavigationController, UIBarButtonItem openMenuButton)
        : base(rootViewController)
    {
        openMenuButton.Clicked += (s, e) => slideoutNavigationController.Open(true);
        rootViewController.NavigationItem.LeftBarButtonItem = openMenuButton;
    }

   public override void ViewDidLoad()
    {
        base.ViewDidLoad();
        this.Delegate = new NavigationControllerDelegate();
        InteractivePopGestureRecognizer.Enabled = true;

    }
   public override void PushViewController(UIViewController viewController, bool animated)
    {
        // To avoid corruption of the navigation stack during animations disabled the pop gesture
        if (InteractivePopGestureRecognizer != null)
            InteractivePopGestureRecognizer.Enabled = false;
        base.PushViewController(viewController, animated);
    }

    private class NavigationControllerDelegate : UINavigationControllerDelegate
    {
        public override void DidShowViewController(UINavigationController navigationController, UIViewController viewController, bool animated)
        {
            // Enable the gesture after the view has been shown
            navigationController.InteractivePopGestureRecognizer.Enabled = true;
        }
    }
}

编辑-做出Jason建议的更改后的结果

---

谁能帮我看看我做错了什么。

在AppDelegate中执行此操作：

    tabs = new UITabBarController();
    tabs.ViewControllers = new UIViewController[]{ 
        new UINavigationController(new UIViewController() { Title = "Tab A" }),
        new UINavigationController(new UIViewController() { Title = "Tab B" }),
        new UINavigationController(new UIViewController() { Title = "Tab C" })
    };

    Menu = new SlideoutNavigationController();
    Menu.MainViewController = new MainNavigationController(tabs, Menu);
    Menu.MenuViewController = new MenuNavigationController(new DummyControllerLeft(), Menu) { NavigationBarHidden = true };

---

我终于找到了解决这个问题的办法。对于任何使用Dillan解决方案并将TabBarController类作为菜单类之一的人，下面是我如何让它工作的

除了MainNavigationController类之外，我将TabBarController类包装在NavigationController中。在此之后，我不必将每个选项卡包装在它自己的NavigationController中。这解决了TabBarController类中对NavigationController的空引用

为了解决每个选项卡中标题模糊的问题，我找到了一个简单的解决方案：

public override void ViewDidLoad ()
{
    base.ViewDidLoad ();

    try{

            this.ViewControllerSelected += (object sender, UITabBarSelectionEventArgs e) => {

            switch(TabBar.SelectedItem.Title)
            {
            case"TAB 1" :

                Title = "TAB 1";
                break;

            case "TAB 2":   
              Title = "TAB 2";
                break;

            default:
                Title = "TAB 3";
                break;
            }
        };


    }catch(Exception e)
    {
        Console.WriteLine (e.Message);
    }
}

---

要知道您正在做什么有点困难，但首先，每个选项卡都应该包含一个单独的导航控制器，每个导航控制器都将包含该选项卡的视图。选项卡控制器本身应该是根视图，不应该包含在导航控制器中。感谢Jason的回复。我同意你的观点，选项卡控制器是根视图，每个选项卡都有一个导航控制器。我已经试过了，我很想坚持下去。挑战在于，我需要实现一个带有选项卡栏控制器的侧导航抽屉，在web上找不到任何侧抽屉不是根视图的实现。这让我别无选择，只能将其作为根视图而不是选项卡栏控制器。什么是MainNavigationController？为什么不直接将选项卡栏控制器分配给Menu.MainViewController？它是导航控制器类。我们基本上是把UIViewController传递给它，这样它就把它们推到堆栈上。我将在那里添加类。不能将选项卡控制器包装到导航控制器中。每个标签都需要自己的导航控制器。我将这些更改替换为第一次启动应用程序时，标签显示在底部，但导航栏上没有屏幕标题。单击抽屉并滚动某些菜单选项并返回主页后，导航栏上仍然没有标题，而底部的选项卡消失。我添加了图像编辑。您需要选择不同的菜单实现。我认为您正在使用的一个不适用于选项卡-它假定正在使用单个导航控制器。Xamarin组件商店中提供了几种不同的标签。您对标签有什么特别的建议吗？我已经试过了FlioutNavigation组件，但它不能很好地与选项卡配合使用。谢谢Jason的帮助。我决定把所有的标签都拿出来，然后只看菜单项。