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我的 ViewModel 中有 4 个实现 IPage 接口（我创建的接口）的类。在我的应用程序的 ViewModel 中，我有一个 IPage 类型的 CurrentPage 属性。

在我的应用程序的 View 层中，我有一个 ContentControl，它的 Content 绑定到 CurrentPage 属性。

因此，当我使用以下代码时，WPF 将找不到正确的 DataTemplate

<UserControl ...>
    <ContentControl Content="{Binding CurrentPage, Mode=OneWay}"
                    VerticalAlignment="Stretch" HorizontalAlignment="Stretch">
        <ContentControl.Resources>
            <DataTemplate DataType="{x:Type operation:OperationListPageVM}">
                <pages1:OperationListPageV/>
            </DataTemplate>
            <DataTemplate DataType="{x:Type operation:OperationDetailPageVM}">
                <pages1:OperationDetailPageV/>
            </DataTemplate>
            <DataTemplate DataType="{x:Type part:PartListPageVM}">
                <pages1:PartListPageV/>
            </DataTemplate>
            <DataTemplate DataType="{x:Type part:PartDetailPageVM}">
                <pages1:PartDetailPageV/>
            </DataTemplate>
            <DataTemplate DataType="{x:Type pages:SettingsPageVM}">
                <pages1:SettingsPageV/>
            </DataTemplate>
        </ContentControl.Resources>
    </ContentControl>
</UserControl>

但是，如果我只将一个 DataTemplate 作为 ContentControl.ContentTemplate ，那么它将正确应用它

<UserControl ...>
    <ContentControl Content="{Binding CurrentPage, Mode=OneWay}"
                    VerticalAlignment="Stretch" HorizontalAlignment="Stretch">
        <ContentControl.ContentTemplate>
            <DataTemplate DataType="{x:Type operation:OperationListPageVM}">
                <pages1:OperationListPageV/>
            </DataTemplate>
        </ContentControl.ContentTemplate>
    </ContentControl>
</UserControl>

如果我然后将这些 DataTemplates 作为资源放回，给它们一个键并创建一个 DataTemplateSelector 并添加

ContentTemplateSelector="{StaticResource PageTemplateSelector}"

到带有 DataTemplateSelector 的 ControlTemplate，如下所示：

using System.Windows;
using System.Windows.Controls;
using MaintenanceModuleV3.ViewModel;
using MaintenanceModuleV3.ViewModel.Pages;
using MaintenanceModuleV3.ViewModel.Pages.Operation;
using MaintenanceModuleV3.ViewModel.Pages.Part;

namespace MaintenanceModuleV3.View.TemplateSelector {
    public class PageTemplateSelector : DataTemplateSelector {
        public override DataTemplate SelectTemplate(object item, DependencyObject container) {
            if (AppVM.Instance.CurrentPage != null) {
                if (AppVM.Instance.CurrentPage is OperationListPageVM) {
                    return (container as FrameworkElement).FindResource("OperationListPageTemplate") as DataTemplate;
                } else if (AppVM.Instance.CurrentPage is OperationDetailPageVM) {
                    return (container as FrameworkElement).FindResource("OperationDetailPageTemplate") as DataTemplate;
                } else if (AppVM.Instance.CurrentPage is PartListPageVM) {
                    return (container as FrameworkElement).FindResource("PartListPageTemplate") as DataTemplate;
                } else if (AppVM.Instance.CurrentPage is PartDetailPageVM) {
                    return (container as FrameworkElement).FindResource("PartDetailPageTemplate") as DataTemplate;
                } else if (AppVM.Instance.CurrentPage is SettingsPageVM) {
                    return (container as FrameworkElement).FindResource("SettingsPageTemplate") as DataTemplate;
                }
            }
            return null;
        }
    }
}

然后选择正确的 DataTemplate。

如果我在这种情况下将 DataTemplates 放在元素资源中，为什么 WPF 不会选择正确的 DataTemplate？

谢谢

注意：使用框架 3.5

编辑：我注意到第二个问题：DataTemplates 中的 DataContext 为空。这是为什么？他们为什么不将 CurrentPage 作为 DataContext？当我直接设置 ContentTemplate 也是这种情况。WPF 似乎不喜欢绑定到接口类型的属性。

编辑 2：如果我在其构造函数中明确设置 OperationListPageV 的 DataContext 并使用 TemplateSelector 一切正常，但为什么我必须使用这些？

编辑 3：完整的 ViewModel 代码，如果有帮助的话：

应用程序视图模型

public class AppVM : INotifyPropertyChanged {

    #region constructor
    private AppVM() {
        AppM.LanguageChanged += (sender, args) => {
            onPropertyChanged("CurrentLanguage");
        };

        AppM.NbDaysAvgChanged += (sender, args) => {
            onPropertyChanged("NbDaysAvg");
        };

        AppM.NbDaysMenuNotificationChanged += (sender, args) => {
            onPropertyChanged("NbDaysMenuNotification");
        };
    }
    #endregion

    #region business

    #endregion

    #region events
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void onPropertyChanged(string propertyName) {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
    }
    #endregion

    #region properties

    private static AppVM _instance;
    public static AppVM Instance {
        get { return _instance ?? (_instance = new AppVM()); }
    }


    #region notifypropertychanged
    private OperationListPageVM _currentPage = OperationListPageVM.Instance;
    public OperationListPageVM CurrentPage {
        get { return _currentPage; }
        set {
            _currentPage = value;
            onPropertyChanged("CurrentPage");
        }
    }

    public Language CurrentLanguage {
        get { return AppM.CurrentLanguage; }
    }

    public int NbDaysMenuNotification {
        get { return AppM.NbDaysMenuNotification; }
    }

    public int NbDaysAvg {
        get { return AppM.NbDaysAvg; }
    }

    public Dictionary<String, String> AvailableTranslations {
        get { return AppM.AvailableTranslations; }
    }
    #endregion
    #region commands
    #endregion
    #endregion
}

我要显示 ViewModel 的页面

public sealed class OperationListPageVM : INotifyPropertyChanged, IPage {

    #region constructor
    private OperationListPageVM() {
        //fill the available operations with data stored in the App Model coming from the DataBase
        foreach (MaintenanceOperation operation in AppM.Operations) {
            AvailableOperations.Add(new MaintenanceOperationVM(operation)); 
        }
        foreach (MaintenanceOperationVM operation in AvailableOperations) {
            DisplayedOperations.Add(operation);
        }
    }
    #endregion

    #region business

    #endregion

    #region events
    public event PropertyChangedEventHandler PropertyChanged;

    private void onPropertyChanged(string propertyName) {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
    }
    #endregion

    #region properties

    private static OperationListPageVM _instance;

    public static OperationListPageVM Instance {
        get { return _instance ?? (_instance = new OperationListPageVM()); }
    }

    #region notifypropertychanged
    private ObservableCollection<MaintenanceOperationVM> _displayedOperations = new ObservableCollection<MaintenanceOperationVM>();
    public ObservableCollection<MaintenanceOperationVM> DisplayedOperations {
        get { return _displayedOperations; }
        set {
            _displayedOperations = value;
            onPropertyChanged("DisplayedOperations");
        }
    }

    private readonly List<MaintenanceOperationVM> _availableOperations = new List<MaintenanceOperationVM>();

    internal List<MaintenanceOperationVM> AvailableOperations {
        get { return _availableOperations; }
    }

    #endregion

    #region commands

    #endregion

    #endregion
}

我要显示的页面的视图层（OperationListPageV）

<UserControl x:Class="MaintenanceModuleV3.View.Pages.OperationListPageV"
            ...>
    <touch:ScrollFriction2>
        <ListBox ItemsSource="{Binding DisplayedOperations}">
                <ListBox.ItemContainerStyle>
                    <Style TargetType="{x:Type ListBoxItem}">
                        <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
                    </Style>
                </ListBox.ItemContainerStyle>
            <ListBox.ItemTemplate>
                <DataTemplate DataType="{x:Type viewModel:MaintenanceOperationVM}">
                    <view:MaintenanceOperationV/>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </touch:ScrollFriction2>
</UserControl>

如果您需要更多代码，请索取。谢谢！

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1 回答 1

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将模板放在 ItemControl 的资源中。我不知道他们为什么这样做，但他们应该比你的 ContentControl 高一级

于 2017-12-06T12:43:07.570 回答