ios - MvvmCross Tabs Controller 包装到 UINavigation Controller 中？

Question

我正在使用 Xamarin.iOS 和 MvvmCross 5.x。我的 Root View 是选项卡 Controller ，我希望任何显示 child 的请求都会强制在选项卡之外(而不是内部)进行堆栈导航。

所以我将我的 Root View 定义如下:

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

不幸的是，根导航 Controller 不是 UINavigationController (正如我所期望的基于属性)，而是 HomeView 本质上是选项卡 View ，我无法实现我的目标。

然后我覆盖了 ios Presenter 以手动创建根 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);
    }
}

但是这段代码在尝试设置 Controller 时在 MvvmCross 深处的某个地方失败了 base.SetWindowRootViewController(_rootViewController)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 Root View 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