棱镜Xamarin表单视图在设置值并调用ViewModel中的raisepropertychangy之后不会更新

Question

i无法绑定值以从视图模型查看，我可以看到值是设置（productList）并在调试时调用raisepropertychanged;我相信代码是正确的，因为当我将其设置为app.cs（navigationservice.navigateasync（" studentpage/navigationpage/navereReveEmpage"）中的第一个页面时）;）;）;），它在从另一个页面上呼叫/导航到SundortErceEmpage。

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"
             xmlns:prism="clr-namespace:Prism.Mvvm;assembly=Prism.Forms"
             prism:ViewModelLocator.AutowireViewModel="True"
             x:Class="mySeeds.Views.StudentRedeemPage"
             Title="Redeem">
    <ContentPage.Content>
        <Grid x:Name="MainGrid">
            <Grid.RowDefinitions>
                <RowDefinition Height="2*" />
                <RowDefinition Height="3*" />
            </Grid.RowDefinitions>
            <Grid Grid.Row="0" 
                  Grid.RowSpan="1" 
                  HorizontalOptions="FillAndExpand" 
                  VerticalOptions="FillAndExpand" 
                  BackgroundColor="{StaticResource RedeemBanner}">
                <Grid.RowDefinitions>
                    <RowDefinition Height="3*"/>
                    <RowDefinition Height="1*"/>
                </Grid.RowDefinitions>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="6*" />
                    <ColumnDefinition Width="4*" />
                </Grid.ColumnDefinitions>
                <Image Source="Icon" 
                       VerticalOptions="Center" 
                       HorizontalOptions="Center" 
                       Grid.Column="1"
                       Grid.Row="0"/>
                <StackLayout Grid.Column="0"
                             Grid.Row="0"
                             HorizontalOptions="CenterAndExpand" 
                             VerticalOptions="Center">
                    <Label Text="REWARD SHOP"
                           TextColor="White"
                           FontSize="Medium"
                           FontAttributes="Bold"
                           VerticalTextAlignment="Center"
                           LineBreakMode="TailTruncation"/>
                    <Label Text="{Binding User_Profile_Table.Points_Earned, StringFormat='{0} Seeds'}"
                           TextColor="White"
                           FontSize="Large"
                           FontAttributes="Bold"
                           VerticalTextAlignment="Center"
                           LineBreakMode="WordWrap"/>
                </StackLayout>
                <StackLayout Grid.Row="1" Grid.ColumnSpan="2" >
                    <Label Text="Partners" BackgroundColor="{StaticResource RedeemTab}" HorizontalOptions="FillAndExpand" VerticalOptions="Center" />
                    <ListView 
                            Margin="0,0,0,0" 
                            HorizontalOptions="FillAndExpand" 
                            VerticalOptions="FillAndExpand" 
                            ItemsSource="{Binding ProductList}"
                            HasUnevenRows="true"
                            CachingStrategy="RecycleElement">
                        <ListView.ItemTemplate>
                            <DataTemplate>
                                <ViewCell>
                                    <Grid Padding="0, 0, 10, 0">
                                        <Grid.RowDefinitions>
                                            <RowDefinition Height="Auto"/>
                                        </Grid.RowDefinitions>
                                        <Grid.ColumnDefinitions>
                                            <ColumnDefinition Width="30"/>
                                            <ColumnDefinition Width="*"/>
                                            <ColumnDefinition Width="Auto"/>
                                        </Grid.ColumnDefinitions>
                                        <Image x:Name="Img"
                                       Grid.Row="0" Grid.Column="0"
                                       HorizontalOptions="Center"
                                       VerticalOptions="Center"
                                       HeightRequest="30"
                                       WidthRequest="30"
                                       Source="{Binding ImageUrl}"/>
                                        <StackLayout Grid.Row="0" Grid.Column="1" VerticalOptions="Center">
                                            <Label Text="{Binding SalesPriceIncVat,StringFormat='{0} Seeds'}"
                                       TextColor="{StaticResource RedeemStatusBar}"
                                       FontAttributes="Bold"
                                       VerticalOptions="Center"/>
                                            <Label Text="{Binding Name}"
                                       VerticalOptions="Center"/>
                                        </StackLayout>
                                        <Button x:Name="btnRedeem"
                                        Text="GET IT!"
                                        TextColor="White"
                                        BackgroundColor="{StaticResource RedeemLightGreen}"
                                        Grid.Row="0" Grid.Column="2">
                                        </Button>
                                    </Grid>
                                </ViewCell>
                            </DataTemplate>
                        </ListView.ItemTemplate>
                    </ListView>
                </StackLayout>
            </Grid>
        </Grid>
    </ContentPage.Content>
</ContentPage>

ViewModel

public class StudentRedeemPageViewModel : NavigationViewModelBase
{
    private List<Data> _productList;
    public List<Data> ProductList
    {
        get { return _productList; }
        set
        {
            SetProperty(ref _productList, value);
            RaisePropertyChanged(nameof(ProductList));
        }
    }
    private User_Profile_Table user_Profile_Table;
    public User_Profile_Table User_Profile_Table
    {
        get { return user_Profile_Table; }
        set
        {
            SetProperty(ref user_Profile_Table, value);
            RaisePropertyChanged(nameof(User_Profile_Table));
        }
    }
    private ProductModel _product_Table;
    public ProductModel Product_Table
    {
        get { return _product_Table; }
        set
        {
            SetProperty(ref _product_Table, value);
            RaisePropertyChanged(nameof(Product_Table));
        }
    }
    public DelegateCommand GetProductListCommand { get; private set; }
    public DelegateCommand UserProfileCommand { get; private set; }
    public DelegateCommand NavigateToRedeemPage { get; set; }
    private IRequestProvider _requestProvider;
    public StudentRedeemPageViewModel(IDeviceService deviceService, INavigationService navigationService,
        IPageDialogService pageDialogService, IRequestProvider requestProvider)
        : base(deviceService, navigationService, pageDialogService)
    {
        _requestProvider = requestProvider;
        NavigateToRedeemPage = new DelegateCommand(() => NavigateCommand.Execute("VocherPage"));
        GetProductListCommand = new DelegateCommand(async () => await GetProductList());
        UserProfileCommand = new DelegateCommand(async () => await GetUserProfile());

        UserProfileCommand.Execute();
        GetProductListCommand.Execute();
    }
    async Task GetProductList()
    {
        List<Data> Test = new List<Data>();
        string username = "[e-mail]";
        string password = "xxxxxxxxx";
        string svcCredentials = Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(username + ":" + password));
        if (svcCredentials != null)
        {
            var client = new HttpClient();
            client.BaseAddress = new Uri("https://xxxxxx.com/");
            client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", svcCredentials);
            var productsResponse = await client.GetAsync("xxxxxx/api/xxxx/");
            var productsJson = productsResponse.Content.ReadAsStringAsync().Result;
            ProductModel members = JsonConvert.DeserializeObject<ProductModel>(productsJson);
            ProductList = members.Data;
        }
    }
    async Task GetUserProfile()
    {
        User_Profile_Table = await _requestProvider.GetAsync<User_Profile_Table>(
            GlobalSetting.Instance.UserProfileTableEndpoint, Settings.AuthAccessToken);
    }
}

模型

public class ProductModel
{
    public List<Data> Data { get; set; }
    public string FirstItem { get; set; }
    public string HasNextPage { get; set; }
    public string HasPreviousPage { get; set; }
    public string LastItem { get; set; }
    public string PageNumber { get; set; }
    public string PageSize { get; set; }
    public string TotalItems { get; set; }
    public string TotalPages { get; set; }
}
public class Data
{
    [JsonProperty("Data")]
    public string ProductId { get; set; }
    public string PartnerId { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public string SalesPriceIncVat { get; set; }
    public string SalesPriceExcVat { get; set; }
    public string SalesVat { get; set; }
    public string ValidFromDateUtc { get; set; }
    public string ValidToDateUtc { get; set; }
    public string TermsAndConditions { get; set; }
    public string UsageInstructions { get; set; }
    public string SlaTime { get; set; }
    public string SlaText { get; set; }
    public string Units { get; set; }
    public string StockRequired { get; set; }
    public string UseVariableValues { get; set; }
    public string MinVariableValue { get; set; }
    public string MaxVariableValue { get; set; }
    public string VariableValueAllowedIncrements { get; set; }
    public string ImageUrl { get; set; }
    public string ImageCaption { get; set; }
    public string CurrentStockBalance { get; set; }
}

Answer 1

如何将视图模型绑定到视图，上面没有bindingContext。