如何在具有棱镜的Xamarin表单中为contentview创建单独的视图模型？

Question

问题陈述我想创建一个contentview用户控件，它有自己的视图模型，可以在多个内容页面中使用。

以下实现中的问题我已经扩展了我的App.xaml.cs，如下所述。但是，一旦导航在具有contentview用户控件的内容页面上工作，但如果我再次导航到该页面，则导航不起作用。只是为了添加它，view.Parent在下面的代码中也是null。

请帮忙。

using OEP.Views;
using Prism;
using Prism.Common;
using Prism.Ioc;
using Prism.Mvvm;
using Prism.Navigation;
using Prism.Unity;
using Unity.Resolution;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;

[assembly: XamlCompilation(XamlCompilationOptions.Compile)]
namespace OEP
{
    public partial class App : PrismApplication
    {
        public App() : this(null) { }

        public App(IPlatformInitializer initializer) : base(initializer) { }

        protected override async void OnInitialized()
        {
            InitializeComponent();
            //await NavigationService.NavigateAsync("NewOrderPage");
            await NavigationService.NavigateAsync("LoginPage");
            //await NavigationService.NavigateAsync("HomePage");
        }

        protected override void RegisterTypes(IContainerRegistry containerRegistry)
        {
            containerRegistry.RegisterForNavigation<LoginPage>();
            containerRegistry.RegisterForNavigation<ForgotPasswordPage>();
            containerRegistry.RegisterForNavigation<HomePage>();
            containerRegistry.RegisterForNavigation<CustomerDetailsPage>();
            containerRegistry.RegisterForNavigation<NewOrderPage>();
            //Container.Resolve<HomePageCustomersUserControl>("Customers");
            //containerRegistry.Register<HomePageCustomersUserControl, HomePageCustomersUserControlViewModel>();
            //ViewModelLocationProvider.Register<HomePageCustomersUserControl>(() => Container.Resolve<HomePageCustomersUserControlViewModel>());
        }

        protected override void ConfigureViewModelLocator()
        {
            ViewModelLocationProvider.SetDefaultViewModelFactory((view, type) =>
            {
                Page page = null;
                switch (view)
                {
                    case Page page1:
                        page = page1;
                        break;
                    case Element customView:
                        page = GetPageFromElement(customView);
                        // Existing parameter with the Page
                        break;
                }

                var navService = CreateNavigationService(page);
                ParameterOverrides overrides = new ParameterOverrides
                {
                        { "navigationService", navService }
                };
                return Container.GetContainer().Resolve(type, type.GetType().Name, overrides);

            });
        }

        // Currently exists
        protected INavigationService CreateNavigationService(Page page)
        {
            var navigationService = NavigationService;
            ((IPageAware)navigationService).Page = page;
            return navigationService;
        }

        protected INavigationService CreateNavigationService(object view)
        {
            switch (view)
            {
                case Page page:
                    return CreateNavigationService(page);
                case Element element:
                    var parentPage = GetPageFromElement(element);
                    if (parentPage == null)
                    {
                        return null;
                    }
                    return CreateNavigationService(parentPage);
                default:
                    return null;
            }
        }

        private Page GetPageFromElement(Element view)
        {
            switch (view.Parent)
            {
                case Page page:
                    return page;
                case null:
                    return null;
                default:
                    return GetPageFromElement(view.Parent);
            }
        }

        protected override void OnStart()
        {
            // Handle when your app starts
        }

        protected override void OnSleep()
        {
            // Handle when your app sleeps
        }

        protected override void OnResume()
        {
            // Handle when your app resumes
        }
    }
}

Answer 1

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