Question

操作系统：Windows 8.1
IDE ：VS 2013 Express for Windows
项目：通用
目标：Windows 8.1，Phone 8.1
IoC ：MEF

我的Windows应用程序基于本指南＆＃34; Hierarchical navigation, start to finish＆＃34;在 Windows开发人员中心上。我使用MEF将ViewModel注入视图。

MainPage 位于 .Shared Project 和 HubPage ， ItemPage 和 SectionPage < / strong>在视角窗口和电话项目。

每个页面都有自己的 ViewModel ，位于程序集中，名为 UILogic 。在启动期间，所有 ViewModels 都成功注入视图。但是，查看立即窗口，我得到此绑定错误：

Windows 8.1

Error: BindingExpression path error: 'HubSectionHeaderCommand' property not found on 'NathsarTS.UILogic.ViewModels.MainPageViewModel, NathsarTS.UILogic, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. BindingExpression: Path='HubSectionHeaderCommand' DataItem='NathsarTS.UILogic.ViewModels.MainPageViewModel, NathsarTS.UILogic, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'; target element is 'Microsoft.Xaml.Interactions.Core.InvokeCommandAction' (Name='null'); target property is 'Command' (type 'ICommand') Error: BindingExpression path error: 'DefaultDataModel' property not found on 'NathsarTS.UILogic.ViewModels.MainPageViewModel, NathsarTS.UILogic, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. BindingExpression: Path='DefaultDataModel' DataItem='NathsarTS.UILogic.ViewModels.MainPageViewModel, NathsarTS.UILogic, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'; target element is 'Windows.UI.Xaml.Data.CollectionViewSource' (Name='null'); target property is 'Source' (type 'Object') Error: BindingExpression path error: 'NavigationHelper' property not found on 'NathsarTS.Views.HubPage'. BindingExpression: Path='NavigationHelper.GoBackCommand' DataItem='NathsarTS.Views.HubPage'; target element is 'Windows.UI.Xaml.Controls.Button' (Name='backButton'); target property is 'Command' (type 'ICommand') Error: BindingExpression path error: 'Section3Items' property not found on 'NathsarTS.UILogic.ViewModels.MainPageViewModel, NathsarTS.UILogic, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. BindingExpression: Path='Section3Items' DataItem='NathsarTS.UILogic.ViewModels.MainPageViewModel, NathsarTS.UILogic, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'; target element is 'Windows.UI.Xaml.Controls.HubSection' (Name='null'); target property is 'DataContext' (type 'Object')

MainPage 如下所示：

<Grid x:Name="LayoutRoot" Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"> <Frame x:Name="rootFrame"/>

HubPage 看起来像这样在启动时也会导航：

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"> ... .. <Hub > <interactivity:Interaction.Behaviors> <core:EventTriggerBehavior EventName="SectionHeaderClick"> <core:InvokeCommandAction Command="{Binding HubSectionHeaderCommand}"/> </core:EventTriggerBehavior> </interactivity:Interaction.Behaviors> <Hub.Header>  <Grid> ... .. <Button x:Name="backButton" Style="{StaticResource NavigationBackButtonNormalStyle}" Margin="0,0,39,0" VerticalAlignment="Top" Command="{Binding NavigationHelper.GoBackCommand, ElementName=pageRoot}" AutomationProperties.Name="Back" AutomationProperties.AutomationId="BackButton" AutomationProperties.ItemType="Navigation Button"/> ... .. </Grid> </Hub.Header> ... .. <HubSection IsHeaderInteractive="True" DataContext="{Binding Section3Items}" d:DataContext="{Binding Groups[3], Source={d:DesignData Source=../NathsarTS.Shared/DataModel/SampleData.json, Type=data:SampleDataSource}}" x:Uid="Section3Header" Header="Section 3" Padding="40,40,40,32"> <DataTemplate> <GridView x:Name="itemGridView" ItemsSource="{Binding Items}" Margin="-9,-14,0,0" AutomationProperties.AutomationId="ItemGridView" AutomationProperties.Name="Items In Group" ItemTemplate="{StaticResource Standard310x260ItemTemplate}" SelectionMode="None" IsSwipeEnabled="false" IsItemClickEnabled="True"> <interactivity:Interaction.Behaviors> <core:EventTriggerBehavior EventName="ItemClick"> <core:InvokeCommandAction Command="{Binding HubSectionGridItemCommand}"/> </core:EventTriggerBehavior> </interactivity:Interaction.Behaviors> </GridView> </DataTemplate> </HubSection> ... .. </Hub>

我的绑定报告未在 MainPageViewModel 上报告，但它们在 HubPageViewModel 中定义。

我 MEF 以这种方式注入 ViewModels ：

[Export(typeof(HubPage))] public sealed partial class HubPage : Page { public HubPage() { this.InitializeComponent(); Debug.WriteLine("HubPage InitializeComponent"); } [Import] public NathsarTS.UILogic.Interfaces.IHubPageViewModel ViewModel { set { this.DataContext = value; } get { return DataContext as NathsarTS.UILogic.Interfaces.IHubPageViewModel; } } /// <summary> /// Called when a part's imports have been satisfied and it is safe to use. /// </summary> [OnImportsSatisfied] public void OnImportsSatisfied() { // IPartImportsSatisfiedNotification is useful when you want to coordinate doing some work // with imported parts independent of when the UI is visible. Debug.WriteLine("HubPage OnImportsSatisfied instantiation"); //NathsarTS.UILogic.Interfaces.IObservableService ObservableService = ServiceLocator.Current.GetInstance<NathsarTS.UILogic.Interfaces.IObservableService>(); this.ViewModel.NavigationHelper = new NathsarTS.Common.Logic.NavigationHelper(this); this.ViewModel.NavigationHelper.LoadState += this.ViewModel.NavigationHelperLoadState; } }
WinRT 中是否允许 ViewModels PageView ？

IN ADDTION ：我在启动时也注意到这一点，HubPage正在初始化两次。为什么：

MainPage InitializeComponent
PropertiesService instantiation
MainPageViewModel instantiation
MainPage OnImportsSatisfied instantiation
HubPage InitializeComponent
HubPageViewModel instantiation
HubPage OnImportsSatisfied instantiation
HubPage InitializeComponent
HubPage OnNavigatedTo instantiation

这是我在创业期间所做的事情：

protected override async void OnLaunched(LaunchActivatedEventArgs args)
{
    this._configuration.WithAssembly(typeof(App).GetTypeInfo().Assembly)
        .WithAssembly(typeof(NathsarTS.UILogic.UILogicBusinessLogic).GetTypeInfo().Assembly)
        .WithAssembly(typeof(NathsarTS.Common.CommonBusinessLogic).GetTypeInfo().Assembly)
        .WithAssembly(typeof(NathsarTS.ODSDocuments.ODSDocumentsBusinessLogic).GetTypeInfo().Assembly);
    this._compositionHost = this._configuration.CreateContainer();

    await ShowWindow(args);
}

private async Task ShowWindow(LaunchActivatedEventArgs e)
{
    MainPage mainPage = Window.Current.Content as MainPage;
    Frame rootFrame = null;

    // Do not repeat app initialization when the Window already has content,
    // just ensure that the window is active
    if (mainPage == null)
    {
        mainPage = _compositionHost.GetExport<MainPage>();
    }

    // Retrieve the root Frame to act as the navigation context and navigate to the first page
    // Don't change the name of "rootFrame" in MainPage.xaml unless you change it here to match.
    rootFrame = (Frame)mainPage.FindName("rootFrame");
    if (rootFrame != null)
    {
        // Associate the frame with a SuspensionManager key.
        SuspensionManager.RegisterFrame(rootFrame, "AppFrame");

        // TODO: change this value to a cache size that is appropriate for your application
        rootFrame.CacheSize = 1;

        if (e.PreviousExecutionState == ApplicationExecutionState.Terminated)
        {
            // Restore the saved session state only when appropriate
            try
            {
                await SuspensionManager.RestoreAsync();
            }
            catch (SuspensionManagerException)
            {
                //Something went wrong restoring state.
                //Assume there is no state and continue
            }
        }

        // Place the main page in the current Window.
        Window.Current.Content = mainPage;

        if (rootFrame.Content == null)
        {
            // When the navigation stack isn't restored navigate to the first page,
            // configuring the new page by passing required information as a navigation
            // parameter
            HubPage hubPage = _compositionHost.GetExport<HubPage>();
            if (!rootFrame.Navigate(hubPage.GetType(), e.Arguments))
            {
                throw new Exception("Failed to create initial page");
            }
        }

    }

    // Ensure the current window is active
    Window.Current.Activate();
}

谢谢你的帮助！..

Answer 1

能够修复我的重复内容并正确地将 ViewModel 连接到 PageView 。问题是。 Navigation 1）在 MEF 进行初始化后继续重新初始化 Page 构造函数，2）由于某种原因< strong> HubPage DataContext 会丢失。

所以，这就是我解决它的方法：

protected override async Task OnLaunchApplicationAsync(LaunchActivatedEventArgs args)
{
    Debug.WriteLine("OnLaunchApplicationAsync...");

    MainPage mainPage = _compositionHost.GetExport<MainPage>();
    Window.Current.Content = mainPage;
    Frame rootFrame = (Frame)mainPage.FindName("rootFrame");

    if (rootFrame != null)
    {
        if (rootFrame.Content == null)
        {
            // When the navigation stack isn't restored navigate to the first page,
            // configuring the new page by passing required information as a navigation
            // parameter
            HubPage hubPage = _compositionHost.GetExport<HubPage>();
            rootFrame.Content = hubPage;
        }
    }

    Window.Current.Activate();
    await Task.FromResult<object>(null);
}

而不是在初始启动时使用。导航，我只是将页面类型分配给。内容

在WinRT中使用多个ViewModel

1 个答案: