MvvmCross Tabs 控制器包装到 UINavigation 控制器中？

Question

我正在使用 Xamarin.iOS 和 MvvmCross 5.x。我的根视图是选项卡控制器，我希望任何显示孩子的请求都会强制在选项卡外部（而不是内部）进行堆栈导航。

所以我将我的根视图定义如下：

[MvxFromStoryboard]
[MvxRootPresentation(WrapInNavigationController = true)]
public partial class HomeView : MvxTabBarViewController<HomeViewModel>

不幸的是，根导航控制器不是 UINavigationController（我期望基于属性）而是 HomeView，它本质上是选项卡视图，我无法实现我的目标。

然后我覆盖了 ios Presenter 来手动创建根 UINavigationController：

public class MySuperCoolIosViewPresenter : MvxIosViewPresenter
{
    private UINavigationController _rootViewController; 

    public MySuperCoolIosViewPresenter(IMvxApplicationDelegate applicationDelegate, UIWindow window)
        : base(applicationDelegate, window)
    {
    }

    protected override void SetWindowRootViewController(UIViewController controller)
    {
        _rootViewController = new UINavigationController(controller);
        base.SetWindowRootViewController(_rootViewController);
    }

    protected override void ShowChildViewController(UIViewController viewController, MvvmCross.iOS.Views.Presenters.Attributes.MvxChildPresentationAttribute attribute, MvxViewModelRequest request)
    {
        _rootViewController.ShowViewController(viewController, _rootViewController);
    }
}

但是在尝试设置控制器base.SetWindowRootViewController(_rootViewController) 时，此代码在 MvvmCross 深处的某处失败，并出现以下错误：

System.NullReferenceException: Object reference not set to an instance of an object\n  
at MvvmCross.iOS.Views.Presenters.MvxIosViewPresenter.CloseTabBarViewController () [0x00036] in <861dee92d7924acc93d876339b4b95f9>:0  
at MvvmCross.iOS.Views.MvxTabBarViewController.ViewWillDisappear (System.Boolean animated) [0x0001f] in <861dee92d7924acc93d876339b4b95f9>:0 
at (wrapper managed-to-native) ObjCRuntime.Messaging:void_objc_msgSend_IntPtr (intptr,intptr,intptr)  
at UIKit.UIWindow.set_RootViewController (UIKit.UIViewController value)

如何在不为根视图创建额外的 ViewModel 和 View 的情况下实现我的目标（我不喜欢这种方法，因为在这种情况下 Android 会崩溃）

Answer 1

我创建了这个示例，其中包含您所需要的内容：https://github.com/rrispoli/SampleTabs

Answer 2

当我在寻找解决方案时，来自 MvvmCross 的家伙更新了框架以准确解决问题到版本 5.1.1（我使用的是 5.1.0）。 Ios 演示者逻辑已更新，正确地尊重 WrapInNavigationController（之前在选项卡的情况下被忽略）。不幸的是，ShowChildViewController 在 InvalidCastException 之后失败了，但我能够通过将根导航控制器优先于选项卡控制器来处理这个问题

    protected override void ShowChildViewController(UIViewController viewController, MvxChildPresentationAttribute attribute, MvxViewModelRequest request)
    {
        if (viewController is IMvxSplitViewController)
            throw new MvxException("A SplitViewController cannot be presented as a child. Consider using Root instead");

        if (ModalViewControllers.Any())
        {
            if (ModalViewControllers.LastOrDefault() is UINavigationController modalNavController)
            {
                PushViewControllerIntoStack(modalNavController, viewController, attribute.Animated);
                return;
            }

            throw new MvxException($"Trying to show View type: {viewController.GetType().Name} as child, but there is currently a plain modal view presented!");
        }

        // this logic goes first for the root controller 
        if (MasterNavigationController != null)
        {
            PushViewControllerIntoStack(MasterNavigationController, viewController, attribute.Animated);
            return;
        }

        // then try to show child for the tabs
        if (TabBarViewController != null && TabBarViewController.ShowChildView(viewController))
        {
            return;
        }

        base.ShowChildViewController(viewController, attribute, request);
    }

我希望它能节省一些人的时间。