Xamarin iOS NavigationController 返回 null

Question

我仍在学习 Xamarin ios 的基本原理，并根据以下示例 Monotouch.SlideoutNavigation 实现了侧抽屉。在本教程中，有一个主视图控制器类，然后分配一个主导航控制器和一个侧边菜单。

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

我的主屏幕是一个 tabcontroller 类，我试图在这个类中引用导航控制器，但它总是返回 null。

这是我面临的两个挑战：

• 选项卡控制器和单选项卡视图控制器内的导航控制器始终为空
• 我的各个选项卡控制器类的标题未显示在导航栏上。

这是 AppDelegate 类：

[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;
    }
}

MainTabController 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);
            }

  }
 }

MainNavigation 控制器类

 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 - 做出以下 Jason 建议的更改后的结果

有人可以帮我看看我做错了什么。

Answer 1

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 };

Answer 2

我终于找到了解决这个问题的方法。对于使用 Dillan 的解决方案并将 TabBarController 类作为菜单类之一的任何人，这是我如何让它工作的。

1. 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

2. 为了解决每个标签内的标题被遮挡的问题，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);
       }
   }