Question

我对DataBinding没什么问题。我想创建这样的结构：

Header
Item    ItemDetails
Item    ItemDetails
Item    ItemDetails

Header
Item    ItemDetails
Item    ItemDetails

所以，我有自定义ItemTemplate的ListView：

<ListView ItemsSource="{Binding Path=Data}">
        <ListView.Template>
            <ControlTemplate>
                <Border x:Name="Bd" SnapsToDevicePixels="true" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Padding="1">
                <Grid>
                    <ScrollViewer VerticalScrollBarVisibility="Hidden"
                                  HorizontalScrollBarVisibility="Hidden"
                                  x:Name="PART_AnimatedScrollViewer"
                                  Padding="{TemplateBinding Padding}" 
                                  Focusable="false">
                                  <ItemsPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                        </ScrollViewer>
                    </Grid>
                </Border>
            </ControlTemplate>
        </ListView.Template>
        <ListView.ItemTemplate>
            <DataTemplate>
                <Grid>
                    <Grid.RowDefinitions>
                        <RowDefinition/>
                        <RowDefinition/>
                    </Grid.RowDefinitions>
                    <TextBlock Text="{Binding Key}" Background="LightGray"/>
                    <ItemsControl Grid.Row="1" ItemsSource="{Binding Value, IsAsync=True}">
                        <DataTemplate>
                            <Grid>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="auto"/>
                                    <ColumnDefinition Width="*"/>
                                </Grid.ColumnDefinitions>
                                <TextBlock Text="{Binding ItemName}"/>
                                <TextBlock Text="{Binding Description}" />
                            </Grid>
                        </DataTemplate>
                    </ItemsControl>
                </Grid>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>

这是ViewModel：

public class ListViewModel : INotifyPropertyChanged
{
    public ListViewModel()
    {
        _data.Add("ExampleHeader1", new List<MyObjectType>()
                                              {
                                                  new MyObjectType("Example ItemName1", "Description1"),
                                                  new MyObjectType("Example ItemName2", "Description2"),
                                                  new MyObjectType("Example ItemName3", "Description3"),
                                              });
        _data.Add("ExampleHeader2", new List<MyObjectType>()
                                              {
                                                  new MyObjectType("Example ItemName1", "Description1"),
                                                  new MyObjectType("Example ItemName2", "Description2"),
                                                  new MyObjectType("Example ItemName3", "Description3"),
                                                  new MyObjectType("Example ItemName4", "Description4"),
                                              });
        _data.Add("ExampleHeader3", new List<MyObjectType>()
                                              {
                                                  new MyObjectType("Example ItemName1", "Description1"),
                                                  new MyObjectType("Example ItemName2", "Description2"),
                                                  new MyObjectType("Example ItemName3", "Description3"),
                                              });
    }

    private readonly Dictionary<string, List<MyObjectType>> _data = new Dictionary<string, List<MyObjectType>>();
    public IDictionary<string, List<MyObjectType>> Data
    {
        get { return this._data; }
    }

    private KeyValuePair<string, List<MyObjectType>>? selectedKey = null;
    public KeyValuePair<string, List<MyObjectType>>? SelectedKey
    {
        get { return this.selectedKey; }
        set
        {
            this.selectedKey = value;
            this.OnPropertyChanged("SelectedKey");
            this.OnPropertyChanged("SelectedValue");
        }
    }

    public List<MyObjectType> SelectedValue
    {
        get
        {
            if (null == this.SelectedKey)
            {
                return new List<MyObjectType>();
            }

            return this._data[this.SelectedKey.Value.Key];
        }
        set
        {
            this._data[this.SelectedKey.Value.Key] = value;
            this.OnPropertyChanged("SelectedValue");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged(string propName)
    {
        var eh = this.PropertyChanged;
        if (null != eh)
        {
            eh(this, new PropertyChangedEventArgs(propName));
        }
    }
}

如果我将运行此应用程序，我将收到错误：

在使用ItemsSource之前，项目集合必须为空。

我该怎么做才能解决此错误？

Answer 1

错误在于：

<ItemsControl Grid.Row="1" ItemsSource="{Binding Value, IsAsync=True}">
    <DataTemplate>
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="auto"/>
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <TextBlock Text="{Binding ItemName}"/>
            <TextBlock Text="{Binding Description}" />
        </Grid>
    </DataTemplate>
</ItemsControl>

您正在尝试添加DataTemplate作为ItemsControl的孩子。显然，你想要做的是：

<ItemsControl Grid.Row="1" ItemsSource="{Binding Value, IsAsync=True}">
   <ItemsControl.ItemTemplate>
      <DataTemplate>
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="auto"/>
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <TextBlock Text="{Binding ItemName}"/>
            <TextBlock Text="{Binding Description}" />
        </Grid>
      </DataTemplate>
   </ItemsControl.ItemTemplate>
</ItemsControl>

Answer 2

使用ObservableCollection加载List项目。

即使您可以更改DataBound控件，但不建议这样做。而是使用ObservableCollection并使用您要加载的相应列表更改其内容。由于ObservableCollection可以轻松地将通知发送到绑定它的对象，因此UI列表将获得更新。

WPF ListView绑定到IDictionary <string，ienumerable <myobjecttype =“”>＆gt; </string，>

2 个答案: