c# - TreeView SelectedItem 行为 - 双向绑定(bind)在一个方向上不起作用

Question

我创建了一个非常简单的示例来说明我的问题。也许我只是想错了。

我想从我的 TreeView 中选择一个项目 - 我想在 View (蓝色背景)中看到它。

为了实现 TwoWayBinding，我使用了这个行为:Data binding to SelectedItem in a WPF Treeview

public class BindableSelectedItemBehavior : Behavior<TreeView>
{
    #region SelectedItem Property

    public object SelectedItem
    {
        get { return (object)GetValue(SelectedItemProperty); }
        set { SetValue(SelectedItemProperty, value); }
    }

    public static readonly DependencyProperty SelectedItemProperty =
        DependencyProperty.Register("SelectedItem", typeof(object), typeof(BindableSelectedItemBehavior), new UIPropertyMetadata(null, OnSelectedItemChanged));

    private static void OnSelectedItemChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        var item = e.NewValue as TreeViewItem;
        if (item != null)
        {
            item.SetValue(TreeViewItem.IsSelectedProperty, true);
        }
    }

    #endregion

    protected override void OnAttached()
    {
        base.OnAttached();

        this.AssociatedObject.SelectedItemChanged += OnTreeViewSelectedItemChanged;
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();

        if (this.AssociatedObject != null)
        {
            this.AssociatedObject.SelectedItemChanged -= OnTreeViewSelectedItemChanged;
        }
    }

    private void OnTreeViewSelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
    {
        this.SelectedItem = e.NewValue;
    }
}

但如果我点击一个项目，它不会进入 OnSelectedItemChanged 的“if”，因为 e.newValue as TreeViewItem 是 null

我的 XAML 非常简单:

<StackPanel>
    <TreeView xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
      ItemsSource="{Binding Items}">
        <i:Interaction.Behaviors>
            <local:BindableSelectedItemBehavior
                SelectedItem="{Binding Item}" />
        </i:Interaction.Behaviors>
        <TreeView.ItemTemplate>
            <HierarchicalDataTemplate>
                <TextBlock Text="{Binding Text}"/>
            </HierarchicalDataTemplate>
        </TreeView.ItemTemplate>
    </TreeView>
    <TextBox Text="{Binding Item.Text}"/>
</StackPanel>

谢谢大家!

Answer 1

为了方便起见，这里是结合OP 的最终解决方案和 ghrod's answer :

namespace MyPoject.Behaviors
{
  using System.Windows;
  using System.Windows.Controls;
  using System.Windows.Interactivity;

  public class BindableSelectedItemBehavior : Behavior<TreeView>
  {
    #region SelectedItem Property

    public object SelectedItem
    {
      get { return (object)GetValue(SelectedItemProperty); }
      set { SetValue(SelectedItemProperty, value); }
    }
    public static readonly DependencyProperty SelectedItemProperty =
        DependencyProperty.Register(
          nameof(SelectedItem),
          typeof(object),
          typeof(BindableSelectedItemBehavior),
          new FrameworkPropertyMetadata(null, 
            FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, 
            OnSelectedItemChanged));

    static void OnSelectedItemChanged(DependencyObject sender, 
      DependencyPropertyChangedEventArgs e)
    {
      var behavior = (BindableSelectedItemBehavior)sender;
      var generator = behavior.AssociatedObject.ItemContainerGenerator;
      if (generator.ContainerFromItem(e.NewValue) is TreeViewItem item)
        item.SetValue(TreeViewItem.IsSelectedProperty, true);
    }
    #endregion

    protected override void OnAttached()
    {
      base.OnAttached();

      AssociatedObject.SelectedItemChanged += OnTreeViewSelectedItemChanged;
    }

    protected override void OnDetaching()
    {
      base.OnDetaching();

      if (this.AssociatedObject != null)
        AssociatedObject.SelectedItemChanged -= OnTreeViewSelectedItemChanged;
    }

    void OnTreeViewSelectedItemChanged(object sender, 
        RoutedPropertyChangedEventArgs<object> e) =>
      SelectedItem = e.NewValue;
  }
}