TreeView SelectedItem 行为 - 双向绑定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。可能是我想错了。

我想 select 我的 TreeView 的一个项目 - 我想在视图（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;
    }
}

但是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很简单：

<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

SelectedItem TreeView 的属性在您的情况下不 return TreeViewItem。它 return 当前从您绑定的 Items 集合中选择的项目。要从 SelectedItem 获取 TreeViewItem，您需要在此处使用 ItemContainerGenerator：

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

Answer 2

如果您的实际模型对象是 TreeViewItem 类型，您的 OnSelectedItemChanged 将仅传递 TreeViewItem 类型的对象，而 99% 的情况都不会是这种情况。您将不得不从模型对象中检索 TreeViewItem，但如果节点当前折叠，它将不可用，这使得选择折叠节点非常重要。

我已经努力在我的博客中对此进行了非常详尽的解释，包括代码示例 here

Answer 3

为了方便起见，这里是 and 的最终解决方案：

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;
  }
}

TreeView SelectedItem 行为 - 双向绑定在一个方向上不起作用

TreeView SelectedItem Behavior - Two Way Binding does not work in One Direction

c#

wpf

treeview

xaml

behavior