xamarin - Xamarin Forms Prism MVVM 嵌套 TabbedPage 问题

Question

我正在使用带有 Prism MVVM 框架的 Xamarin Forms。

我在做嵌套 TabbedPage 时遇到问题。

例如我有 TabbedPage1。

然后我添加 TabbedPage2 和 Page99 作为 TabbedPage1 的子级。

然后我将 Page1 和 Page2 添加为 TabbedPage2 的子项。

但是结果是 Page1 和 Page2 变成了空白 Page 并且 Page1 和 Page2 的标题变成了 TabbedPage2 的标题

我正在使用 Xamarin 3.1.0.697729 和 Prism 7.0.0.396

这是截图

这是复制完整项目或github 。我举了一个例子，说明使用 mvvm 和不使用 mvvm 的区别。

这是一些源代码

TabbedPage1.xaml

<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         x:Class="AssetKita.Views.TabbedPage1"
        Title="{Binding Title}"
        xmlns:Existing_Page="clr-namespace:AssetKita.Views">

    <ContentPage Title="Tab 1" />
    <ContentPage Title="Tab 2" />
    <ContentPage Title="Tab 3" />
    <Existing_Page:TabbedPage2/>
    <ContentPage Title="Tab 5" />
</TabbedPage>

TabbedPage1.xaml.cs

namespace AssetKita.Views
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class TabbedPage1 : Xamarin.Forms.TabbedPage
    {
        public TabbedPage1 ()
        {
            InitializeComponent();

            On<Xamarin.Forms.PlatformConfiguration.Android>().SetToolbarPlacement(Xamarin.Forms.PlatformConfiguration.AndroidSpecific.ToolbarPlacement.Bottom);
            On<Xamarin.Forms.PlatformConfiguration.Android>().SetBarSelectedItemColor((Color)App.Current.Resources["PrimaryGreenColor"]);
        }
    }
}

TabbedPage2.xaml

<?xml version="1.0" encoding="utf-8" ?>
<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         x:Class="AssetKita.Views.TabbedPage2"
        xmlns:Existing_Page="clr-namespace:AssetKita.Views"
        Title="{Binding Title}">
    <Existing_Page:Page1/>
    <Existing_Page:Page2/>
</TabbedPage>

Page1.xaml 和 Page2.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         x:Class="AssetKita.Views.ItemList_Invest_Page"
         Title="{Binding Title}">

<ListView ItemsSource="{Binding PostItems, Mode=TwoWay}"
          SeparatorVisibility="None"
          CachingStrategy="RecycleElement"
          HasUnevenRows="True"
          x:Name="listview_item">
    <ListView.ItemTemplate>
        <DataTemplate>
            <ViewCell>
                <Frame Padding="0" Margin="10">
                    <Frame.HasShadow>
                        <OnPlatform x:TypeArguments="x:Boolean" iOS="True" Android="True">
                        </OnPlatform>
                    </Frame.HasShadow>
                    <Frame.BorderColor>
                        <OnPlatform x:TypeArguments="Color" iOS="Transparent" Android="Default"/>
                    </Frame.BorderColor>
                    <Frame.BackgroundColor>
                        <OnPlatform x:TypeArguments="Color" iOS="Transparent" Android="Default"/>
                    </Frame.BackgroundColor>
                    <Grid HorizontalOptions="FillAndExpand"
                          VerticalOptions="FillAndExpand"
                          Padding="10"
                          RowSpacing="5"
                          ColumnSpacing="5">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="100"/>
                            <ColumnDefinition Width="Auto"/>
                            <ColumnDefinition Width="10"/>
                            <ColumnDefinition Width="Auto"/>
                            <ColumnDefinition Width="Auto"/>
                        </Grid.ColumnDefinitions>
                        <Grid.RowDefinitions>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="Auto"/>
                        </Grid.RowDefinitions>

                        <Image Grid.Column="0"
                               Grid.Row="0"
                               Grid.RowSpan="5"
                               Margin="0,0,10,0"
                               Source="{Binding IMAGE_LINK}"
                               Aspect="AspectFill"/>

                        <Label Text="{Binding NAME}"
                               FontSize="Medium"
                               FontAttributes="Bold"
                               Grid.Column="1"
                               Grid.Row="0"
                               Grid.ColumnSpan="4"/>

                        <Label Text="Kategori"
                               Grid.Column="1"
                               Grid.Row="1"/>
                        <Label Text="Bunga"
                               Grid.Column="1"
                               Grid.Row="2"/>
                        <Label Text="Durasi"
                               Grid.Column="1"
                               Grid.Row="3"/>

                        <Label Text=":"
                               Grid.Column="2"
                               Grid.Row="1"/>
                        <Label Text=":"
                               Grid.Column="2"
                               Grid.Row="2"/>
                        <Label Text=":"
                               Grid.Column="2"
                               Grid.Row="3"/>

                        <Label Text="{Binding CATEGORY}"
                               Grid.Column="3"
                               Grid.Row="1"/>
                        <Label Text="{Binding ASKING_INTEREST_RATE}"
                               Grid.Column="3"
                               Grid.Row="2"/>
                        <Label Text="{Binding DURATION}"
                               Grid.Column="3"
                               Grid.Row="3"/>
                        <Label x:Name="label_price"
                               FontSize="Medium"
                               TextColor="#FF6F00"
                               Grid.Column="1"
                               Grid.Row="4"
                               Grid.ColumnSpan="4"/>
                    </Grid>
                </Frame>
            </ViewCell>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

Page1ViewModel.cs 和 Page2ViewModel.cs

namespace AssetKita.ViewModels
{
    class Page1ViewModel : ViewModelChild
    {
        private List<PostItem> postItems = new List<PostItem>()
        {
            new PostItem
            {
                NAME = "Emas 24 Karat",
                    ASKING_INTEREST_RATE = "2%",
                    ASKING_PRICE = "1.000.000",
                    CATEGORY = "Emas",
                    DESCRIPTION = "Berat 3 gram",
                    DURATION = "30 hari",
                    IMAGE_LINK = "https://fm.cnbc.com/applications/cnbc.com/resources/img/editorial/2017/10/02/104748034-GettyImages-90075023.530x298.jpg?v=1506995840"
            },
            new PostItem
                {
                    NAME = "Redmi Note 5",
                    ASKING_INTEREST_RATE = "2%",
                    ASKING_PRICE = "2.000.000",
                    CATEGORY = "Smartphone",
                    DESCRIPTION = "Mulus Like New",
                    DURATION = "30 hari",
                    IMAGE_LINK = "http://st1.bgr.in/wp-content/uploads/2018/02/Xiaomi-Redmi-Note-5-Front.jpg"
                },
                new PostItem
                {
                    NAME = "MacBook Pro 15 inch 2018",
                    ASKING_INTEREST_RATE = "2%",
                    ASKING_PRICE = "20.000.000",
                    CATEGORY = "Elektronik",
                    DESCRIPTION = "Mulus Like New",
                    DURATION = "30 hari",
                    IMAGE_LINK = "https://www.insightmac.com/wp-content/uploads/2018/07/26826-38847-2018-MacBook-Pro-15-inch-l.jpg"
                },
        };
        public List<PostItem> PostItems
        {
            get { return postItems; }
            set { SetProperty(ref postItems, value); }
        }

        public ItemList_Invest_ViewModel(INavigationService navigationService,
            IPageDialogService pageDialog)
        {
            Title = "INVEST";
        }
    }
}

ViewModelChild.cs

namespace AssetKita.ViewModels
{
    public class ViewModelChild : ViewModelBase, IActiveAware
    {
        private string _message;
        public string Message
        {
            get { return _message; }
            set { SetProperty(ref _message, value); }
        }

        private bool _isActive;
        public bool IsActive
        {
            get { return _isActive; }
            set { SetProperty(ref _isActive, value, () => System.Diagnostics.Debug.WriteLine($"{Title} IsActive Changed: {value}")); }
        }

        public event EventHandler IsActiveChanged;

        public ViewModelChild()
        {
            IsActiveChanged += (sender, e) => System.Diagnostics.Debug.WriteLine($"{Title} IsActive: {IsActive}");
        }

        public override void OnNavigatingTo(NavigationParameters parameters)
        {
            System.Diagnostics.Debug.WriteLine($"{Title} is executing OnNavigatingTo");
            var message = parameters.GetValue<string>("message");
            Message = $"{Title} Initialized by OnNavigatingTo: {message}";
        }

        public override void Destroy()
        {
            System.Diagnostics.Debug.WriteLine($"{Title} is being Destroyed!");
        }
    }
}

ViewModelBase.cs

namespace AssetKita.ViewModels
{
    public class ViewModelBase : BindableBase, INavigationAware, IDestructible
    {
        protected INavigationService NavigationService { get; private set; }

        private string _title;
        public string Title
        {
            get { return _title; }
            set { SetProperty(ref _title, value); }
        }


        public virtual void OnNavigatedFrom(NavigationParameters parameters)
        {

        }

        public virtual void OnNavigatedTo(NavigationParameters parameters)
        {

        }

        public virtual void OnNavigatingTo(NavigationParameters parameters)
        {

        }

        public virtual void Destroy()
        {

        }
    }
}

PostItem.cs

    namespace AssetKita.Models
    {
        class PostItem
        {
            public string IMAGE_LINK { get; set; }
            public string NAME { get; set; }
            public string WEIGHT { get; set; }
            public string CATEGORY { get; set; }
            public string ASKING_PRICE { get; set; }
            public string ASKING_INTEREST_RATE { get; set; }
            public string DURATION { get; set; }
            public string DESCRIPTION { get; set; }

            public Owner owner { get; set; }
            public string OWNER_LOCATION
            {
                get { return owner.LOCATION; }
                set { owner.LOCATION = value; }
            }
        }
    }

所有者.cs

namespace AssetKita.Models
{
    class PostItem
    {
        public string IMAGE_LINK { get; set; }
        public string NAME { get; set; }
        public string WEIGHT { get; set; }
        public string CATEGORY { get; set; }
        public string ASKING_PRICE { get; set; }
        public string ASKING_INTEREST_RATE { get; set; }
        public string DURATION { get; set; }
        public string DESCRIPTION { get; set; }

        public Owner owner { get; set; }
        public string OWNER_LOCATION
        {
            get { return owner.LOCATION; }
            set { owner.LOCATION = value; }
        }
    }
}

应用程序.xaml.cs

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

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

        protected override async void OnInitialized()
        {
            InitializeComponent();

            await NavigationService.NavigateAsync("NavigationPage/TabbedPage1");
        }

        protected override void RegisterTypes(IContainerRegistry containerRegistry)
        {
            containerRegistry.RegisterForNavigation<NavigationPage>();
            containerRegistry.RegisterForNavigation<TabbedPage1>();
            containerRegistry.RegisterForNavigation<TabbedPage2>();
            containerRegistry.RegisterForNavigation<Page1>();
            containerRegistry.RegisterForNavigation<Page2>();
        }
    }
}