在HierarchicalDataTemplate标签中，转换为TextBlock

Question

在尝试在我的应用程序中实现Drag＆amp; Drop时，我遇到了一些奇怪的行为。我使用HierarchicalDataTemplate在TreeView中表示我的数据结构，如此：

XAML：

<TreeView Name="treeViewNotes" AllowDrop="True" PreviewMouseLeftButtonDown="treeViewNotes_PreviewMouseLeftButtonDown" PreviewMouseMove="treeViewNotes_PreviewMouseMove" Drop="treeViewNotes_Drop" DragEnter="treeViewNotes_DragEnter" SelectedItemChanged="treeViewNotes_SelectedItemChanged">
    <TreeView.Resources>
        <HierarchicalDataTemplate DataType="{x:Type local:NoteCategory}" ItemsSource="{Binding Notes}">
            <StackPanel Orientation="Horizontal">
                <Image Height="16" Source="{Binding TreeViewIcon}" Tag="{Binding Self}"/>
                <Label Content="{Binding Title}" Tag="{Binding Self}" Margin="3"/>
            </StackPanel>
        </HierarchicalDataTemplate>
        <HierarchicalDataTemplate DataType="{x:Type local:TextNote}">
            <StackPanel Orientation="Horizontal">
                <Image Height="16" Source="{Binding TreeViewIcon}" Tag="{Binding Self}"/>
                <Label Content="{Binding Title}" Tag="{Binding Self}" Margin="3"/>
            </StackPanel>
        </HierarchicalDataTemplate>
    </TreeView.Resources>
</TreeView>

CODE：

private void buttonCreateNote_Click(object sender, RoutedEventArgs e)
{
    ObservableCollection<NoteCategory> NoteCategoriesList = new ObservableCollection<NoteCategory>();

    NoteCategory category1 = new NoteCategory("Category 1", Properties.Resources.FolderIcon);
    TextNote textNote1 = new TextNote("Text note 1", Properties.Resources.TextNoteIcon, category1, "Blah blah. Content for note 1");
    TextNote textNote2 = new TextNote("Text note 2", Properties.Resources.TextNoteIcon, category1, "Blah blah. Content for note 2");

    NoteCategory category2 = new NoteCategory("Category 2", Properties.Resources.FolderIcon);
    TextNote textNote4 = new TextNote("Text note 4", Properties.Resources.TextNoteIcon, category2, "Blah blah. Content for note 4");
    TextNote textNote5 = new TextNote("Text note 5", Properties.Resources.TextNoteIcon, category2, "Blah blah. Content for note 5");

    NoteCategoriesList.Add(category1);
    NoteCategoriesList.Add(category2);

    treeViewNotes.ItemsSource = NoteCategoriesList;
}

结果：

这很好用，所以现在我希望能够在类别之间拖放音符，所以我部分地实现了here

中的代码

CODE：

private void treeViewNotes_PreviewMouseMove(object sender, MouseEventArgs e)
{
    Point mousePos = e.GetPosition(null);
    Vector diff = Utils.DragDropStartPoint - mousePos;

    if (Utils.IsDragDropping == false &&
        (e.LeftButton == MouseButtonState.Pressed || e.RightButton == MouseButtonState.Pressed) &&
        (Math.Abs(diff.X) > SystemParameters.MinimumHorizontalDragDistance || Math.Abs(diff.Y) > SystemParameters.MinimumVerticalDragDistance))
    {
        // Get the dragged ListViewItem
        TreeView treeView = sender as TreeView;

        if (e.OriginalSource is Image || e.OriginalSource is Label)
        {
            FrameworkElement elem = e.OriginalSource as FrameworkElement;
            if (elem.Tag == null)
                MessageBox.Show(elem.GetType() + "\n\nNULL");
            else
                MessageBox.Show(elem.GetType() + "\n\n" + elem.Tag.ToString());
        }
        else
            MessageBox.Show(e.OriginalSource.GetType().ToString());
    }
}

整个操作的关键是将Tag绑定到TextNote对象本身，因此当用户拖动Label或Image时，我可以提取它TreeViewItem。它适用于Image。但是，当我尝试通过单击Label来拖动时e.OriginalSource实际上作为带有空标记的TextBlock来到处理程序。无论我在哪里点击并拖动鼠标，我都无法使Label触发事件。问题是为什么？

我在TextBlock中使用HierarchicalDataTemplate而不是标签做了一个解决方法，但它确实有效，但我仍然很好奇为什么其他方法不起作用。