多选模式下，如何获取Windows.UI.Xaml.Controls.TreeView选中节点

一、先修复WinUI TreeView的"No such Interface supported"错误 #

这个错误90%的概率是因为你在DataTemplate里用了系统自带的<TreeViewItem>，而非WinUI命名空间下的<muxc:TreeViewItem>。WinUI的TreeView必须搭配同框架的TreeViewItem使用，否则会出现组件兼容性问题。

修正后的XAML代码 #

<!-- 确保页面顶部已声明WinUI命名空间：xmlns:muxc="using:Microsoft.UI.Xaml.Controls" -->
<muxc:TreeView SelectionMode="Multiple" Width="300" x:Name="CategoriesTree" 
              ItemsSource="{x:Bind _vm.Categories, Mode=OneWay}"
              SelectionChanged="CategoriesTree_SelectionChanged">
      <muxc:TreeView.ItemTemplate>
            <DataTemplate x:DataType="local1:CategoriesInfo">
                      <!-- 替换为WinUI的TreeViewItem -->
                      <muxc:TreeViewItem ItemsSource="{x:Bind SubCategories}" Content="{x:Bind Name}" />
            </DataTemplate>
      </muxc:TreeView.ItemTemplate>
</muxc:TreeView>

额外检查项 #

• 确认项目已安装Microsoft.UI.Xaml NuGet包（建议选稳定版，比如2.8.0）
• 项目目标最低Windows版本需≥Windows 10 1809（10.0.17763.0），WinUI 2对低版本系统支持有限

二、实现多选选中项的双向绑定 #

WinUI的TreeView自带的SelectedItems是只读集合，无法直接双向绑定到ViewModel属性，推荐两种解决方案：

方案1：通过SelectionChanged事件同步选中项 #

在后台代码中监听事件，手动同步到ViewModel的集合：

private void CategoriesTree_SelectionChanged(muxc.TreeView sender, muxc.TreeViewSelectionChangedEventArgs args)
{
    // 清空ViewModel中的选中集合
    _vm.SelectedCategories.Clear();
    // 遍历选中项并添加到ViewModel
    foreach (var item in sender.SelectedItems)
    {
        if (item is CategoriesInfo category)
        {
            _vm.SelectedCategories.Add(category);
        }
    }
}

如果需要反向同步（ViewModel更新时同步TreeView选中状态），可以监听集合变更：

// 假设ViewModel的SelectedCategories是ObservableCollection<CategoriesInfo>
_vm.SelectedCategories.CollectionChanged += (s, e) =>
{
    // 先取消所有选中
    CategoriesTree.DeselectAll();
    // 选中集合内的项
    foreach (var category in _vm.SelectedCategories)
    {
        var container = CategoriesTree.ContainerFromItem(category) as muxc.TreeViewItem;
        container?.IsSelected = true;
    }
};

方案2：自定义附加属性实现双向绑定 #

封装一个附加属性，让XAML可以直接绑定：

public static class TreeViewHelper
{
    public static readonly DependencyProperty SelectedItemsProperty =
        DependencyProperty.RegisterAttached("SelectedItems", typeof(IList), typeof(TreeViewHelper),
            new PropertyMetadata(null, OnSelectedItemsChanged));

    public static IList GetSelectedItems(DependencyObject obj)
    {
        return (IList)obj.GetValue(SelectedItemsProperty);
    }

    public static void SetSelectedItems(DependencyObject obj, IList value)
    {
        obj.SetValue(SelectedItemsProperty, value);
    }

    private static void OnSelectedItemsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (d is muxc.TreeView treeView)
        {
            treeView.SelectionChanged -= OnTreeViewSelectionChanged;
            if (e.NewValue is IList newList)
            {
                treeView.SelectionChanged += OnTreeViewSelectionChanged;
                SyncTreeViewSelection(treeView, newList);
            }
        }
    }

    private static void OnTreeViewSelectionChanged(muxc.TreeView sender, muxc.TreeViewSelectionChangedEventArgs args)
    {
        var selectedItems = GetSelectedItems(sender);
        if (selectedItems == null) return;

        selectedItems.Clear();
        foreach (var item in sender.SelectedItems)
        {
            selectedItems.Add(item);
        }
    }

    private static void SyncTreeViewSelection(muxc.TreeView treeView, IList selectedItems)
    {
        treeView.DeselectAll();
        foreach (var item in selectedItems)
        {
            var container = treeView.ContainerFromItem(item) as muxc.TreeViewItem;
            container?.IsSelected = true;
        }
    }
}

然后在XAML中直接绑定：

<muxc:TreeView SelectionMode="Multiple" Width="300" x:Name="CategoriesTree" 
              ItemsSource="{x:Bind _vm.Categories, Mode=OneWay}"
              local:TreeViewHelper.SelectedItems="{x:Bind _vm.SelectedCategories, Mode=TwoWay}">
      <muxc:TreeView.ItemTemplate>
            <DataTemplate x:DataType="local1:CategoriesInfo">
                      <muxc:TreeViewItem ItemsSource="{x:Bind SubCategories}" Content="{x:Bind Name}" />
            </DataTemplate>
      </muxc:TreeView.ItemTemplate>
</muxc:TreeView>

注意：ViewModel中的SelectedCategories需为ObservableCollection<CategoriesInfo>类型，才能支持双向同步。

内容的提问来源于stack exchange，提问作者Sayansen