为什么 WPF TreeViewItem.Expanded“发件人”通过 TreeView 而不是 TreeViewItem？

Question

如何访问正在展开的 TreeViewItem（或者更确切地说是对象）？在我看来，事件处理程序的“发送者”应该是 TreeViewItem 而不是 TreeView。我想在展开时对绑定到 TreeViewItem 的对象进行操作。

<Window x:Class="MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Title="MainWindow" Height="350" Width="525"
    Loaded="Window_Loaded">
<StackPanel>
    <TreeView x:Name="treeView" HorizontalAlignment="Left" VerticalAlignment="Top" 
              TreeViewItem.Expanded="treeViewItem_Expanded" >
        <TreeView.ItemTemplate>
            <HierarchicalDataTemplate ItemsSource="{Binding}">
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="{Binding Name}" />
                </StackPanel>
            </HierarchicalDataTemplate>
        </TreeView.ItemTemplate>
    </TreeView>
</StackPanel>

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void Window_Loaded(object sender, RoutedEventArgs e)
    {
        Element root = new Element() { Name = "root" };
        Element a1 = new Element() { Name = "a1" };
        Element a2 = new Element() { Name = "a2" };
        Element b1 = new Element() { Name = "b2" };
        root.Add(a1);
        root.Add(a2);
        a2.Add(b1);
        treeView.ItemsSource = root;
     }

    private void treeViewItem_Expanded(object sender, RoutedEventArgs e)
    {
        TreeViewItem tvi = sender as TreeViewItem;
        tvi = e.Source as TreeViewItem;
        TreeView tv = sender as TreeView;
    }

    public interface IElement
    {
        string Name { get; set; }
    }

    public class Element : ObservableCollection<IElement>, IElement
    {
        public string Name { get; set; }
    }
}

Answer 1

使用TreeViewItem.Selected 事件。冒泡到树视图的选定事件（TreeViewItem 本身在设计时不存在，因为我们使用的是 HierarchicalDataTemplate）。

可以在 XAML 中这样捕获事件：

<TreeView TreeViewItem.Selected="TreeViewItemSelected" .../> 

那么最后选择的TreeViewItem可以在事件中设置为：

private void TreeViewItemSelected(object sender, RoutedEventArgs e)
{
    TreeViewItem tvi = e.OriginalSource as TreeViewItem;

    // set the last tree view item selected variable which may be used elsewhere as there is no other way I have found to obtain the TreeViewItem container (may be null)
    this.lastSelectedTreeViewItem = tvi;

    ...
 }