C# 使用 WPF 在虚拟化 TreeView 中选择一个节点

Selecting a node in virtualized TreeView with WPF

提问by pousi

Is there a way to select manually a node in virtualizing TreeView and then bring it into view?

有没有办法在虚拟化 TreeView 中手动选择一个节点，然后将其显示出来？

The data model I'm using with my TreeView is implemented based on the VM-M-V model. Each TreeViewItem's IsSelected property is binded to a corresponing property in ViewModel. I've also created a listener for TreeView's ItemSelected event where I call BringIntoView() for the selected TreeViewItem.

我在 TreeView 中使用的数据模型是基于 VM-MV 模型实现的。每个 TreeViewItem 的 IsSelected 属性都绑定到 ViewModel 中的相应属性。我还为 TreeView 的 ItemSelected 事件创建了一个侦听器，在该事件中我为选定的 TreeViewItem 调用了 BringIntoView()。

The problem with this approach seems to be that the ItemSelected event won't be raised until the actual TreeViewItem is created. So with the virtualization enabled node selection won't do anything until the TreeView is scrolled enough and then it jumps "magically" to the selected node when the event is finally raised.

这种方法的问题似乎是在创建实际的 TreeViewItem 之前不会引发 ItemSelected 事件。因此，在启用虚拟化的情况下，节点选择不会做任何事情，直到 TreeView 滚动到足够的程度，然后当事件最终引发时它“神奇地”跳转到选定的节点。

I'd really like to use virtualization because I have thousands of nodes in my tree and I've already seen quite impressive performance improvements when the virtualization has been enabled.

我真的很喜欢使用虚拟化，因为我的树中有数千个节点，并且在启用虚拟化后，我已经看到了相当可观的性能改进。

回答by Micah

Here is an example taken from an MSDN Questionpublic void ScrollToItem(int index)

这是从MSDN 问题public void ScrollToItem(int index) 中获取的示例

    {

        Dispatcher.BeginInvoke(System.Windows.Threading.DispatcherPriority.Background,

            (System.Windows.Threading.DispatcherOperationCallback)delegate(object arg)

            {

                int N = fileList.Items.Count;

                if (N == 0)

                    return null;

                if (index < 0)

                {

                    fileList.ScrollIntoView(fileList.Items[0]); // scroll to first

                }

                else

                {

                    if (index < N)

                    {

                        fileList.ScrollIntoView(fileList.Items[index]); // scroll to item

                    }

                    else

                    {

                        fileList.ScrollIntoView(fileList.Items[N - 1]); // scroll to last

                    }

                }

                return null;

            }, null);

    }

回答by user88520

I used an attached property to solve this issue.

我使用附加属性来解决这个问题。

public class TreeViewItemBehaviour
{
    #region IsBroughtIntoViewWhenSelected

    public static bool GetIsBroughtIntoViewWhenSelected(TreeViewItem treeViewItem)
    {
        return (bool)treeViewItem.GetValue(IsBroughtIntoViewWhenSelectedProperty);
    }

    public static void SetIsBroughtIntoViewWhenSelected(
      TreeViewItem treeViewItem, bool value)
    {
        treeViewItem.SetValue(IsBroughtIntoViewWhenSelectedProperty, value);
    }

    public static readonly DependencyProperty IsBroughtIntoViewWhenSelectedProperty =
        DependencyProperty.RegisterAttached(
        "IsBroughtIntoViewWhenSelected",
        typeof(bool),
        typeof(TreeViewItemBehaviour),
        new UIPropertyMetadata(false, OnIsBroughtIntoViewWhenSelectedChanged));

    static void OnIsBroughtIntoViewWhenSelectedChanged(
      DependencyObject depObj, DependencyPropertyChangedEventArgs e)
    {
        TreeViewItem item = depObj as TreeViewItem;
        if (item == null)
            return;

        if (e.NewValue is bool == false)
            return;

        if ((bool)e.NewValue)
        {
            item.Loaded += item_Loaded;
        }
        else
        {
            item.Loaded -= item_Loaded;
        }
    }

    static void item_Loaded(object sender, RoutedEventArgs e)
    {
        TreeViewItem item = e.OriginalSource as TreeViewItem;
        if (item != null)
            item.BringIntoView();
    }

    #endregion // IsBroughtIntoViewWhenSelected

}

And in my XAML style for a TreeViewItem, I just set the property to true

在我的 TreeViewItem 的 XAML 样式中，我只是将属性设置为 true

<Setter Property="Behaviours:TreeViewItemBehaviour.IsBroughtIntoViewWhenSelected" Value="True" />

HTH

HTH

回答by splintor

The link Estifanos Kidane gave is broken. He probably meant the "Changing selection in a virtualized TreeView" MSDN sample. however, this sample shows how to select a node in a tree, but using code-behind and not MVVM and binding, so it also doesn't handle the missing SelectedItemChanged eventwhen the bound SelectedItem is changed.

Estifanos Kidane 提供的链接已断开。他的意思可能是“在虚拟化的 TreeView 中更改选择”MSDN 示例。但是，此示例展示了如何选择树中的节点，但使用代码隐藏而不是 MVVM 和绑定，因此当绑定的 SelectedItem 更改时，它也不会处理丢失的SelectedItemChanged 事件。

The only solution I can think of is to break the MVVM pattern, and when the ViewModel property that is bound to SelectedItem property changes, get the View and call a code-behind method (similar to the MSDN sample) that makes sure the new value is actually selected in the tree.

我能想到的唯一解决方案是打破 MVVM 模式，当绑定到 SelectedItem 属性的 ViewModel 属性发生变化时，获取视图并调用代码隐藏方法（类似于 MSDN 示例）以确保新值实际上是在树中选择的。

Here is the code I wrote to handle it. Suppose your data items are of type Nodewhich has a Parentproperty:

这是我为处理它而编写的代码。假设您的数据项的类型Node具有以下Parent属性：

public class Node
{
    public Node Parent { get; set; }
}

I wrote the following behavior class:

我写了以下行为类：

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Reflection;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Interactivity;

public class NodeTreeSelectionBehavior : Behavior<TreeView>
{
    public Node SelectedItem
    {
        get { return (Node)GetValue(SelectedItemProperty); }
        set { SetValue(SelectedItemProperty, value); }
    }

    public static readonly DependencyProperty SelectedItemProperty =
        DependencyProperty.Register("SelectedItem", typeof(Node), typeof(NodeTreeSelectionBehavior),
            new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, OnSelectedItemChanged));

    private static void OnSelectedItemChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var newNode = e.NewValue as Node;
        if (newNode == null) return;
        var behavior = (NodeTreeSelectionBehavior)d;
        var tree = behavior.AssociatedObject;

        var nodeDynasty = new List<Node> { newNode };
        var parent = newNode.Parent;
        while (parent != null)
        {
            nodeDynasty.Insert(0, parent);
            parent = parent.Parent;
        }

        var currentParent = tree as ItemsControl;
        foreach (var node in nodeDynasty)
        {
            // first try the easy way
            var newParent = currentParent.ItemContainerGenerator.ContainerFromItem(node) as TreeViewItem;
            if (newParent == null)
            {
                // if this failed, it's probably because of virtualization, and we will have to do it the hard way.
                // this code is influenced by TreeViewItem.ExpandRecursive decompiled code, and the MSDN sample at http://code.msdn.microsoft.com/Changing-selection-in-a-6a6242c8/sourcecode?fileId=18862&pathId=753647475
                // see also the question at http://stackoverflow.com/q/183636/46635
                currentParent.ApplyTemplate();
                var itemsPresenter = (ItemsPresenter)currentParent.Template.FindName("ItemsHost", currentParent);
                if (itemsPresenter != null)
                {
                    itemsPresenter.ApplyTemplate();
                }
                else
                {
                    currentParent.UpdateLayout();
                }

                var virtualizingPanel = GetItemsHost(currentParent) as VirtualizingPanel;
                CallEnsureGenerator(virtualizingPanel);
                var index = currentParent.Items.IndexOf(node);
                if (index < 0)
                {
                    throw new InvalidOperationException("Node '" + node + "' cannot be fount in container");
                }
                CallBringIndexIntoView(virtualizingPanel, index);
                newParent = currentParent.ItemContainerGenerator.ContainerFromIndex(index) as TreeViewItem;
            }

            if (newParent == null)
            {
                throw new InvalidOperationException("Tree view item cannot be found or created for node '" + node + "'");
            }

            if (node == newNode)
            {
                newParent.IsSelected = true;
                newParent.BringIntoView();
                break;
            }

            newParent.IsExpanded = true;
            currentParent = newParent;
        }
    }

    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.SelectedItemChanged += OnTreeViewSelectedItemChanged;
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();
        AssociatedObject.SelectedItemChanged -= OnTreeViewSelectedItemChanged;
    }

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

    #region Functions to get internal members using reflection

    // Some functionality we need is hidden in internal members, so we use reflection to get them

    #region ItemsControl.ItemsHost

    static readonly PropertyInfo ItemsHostPropertyInfo = typeof(ItemsControl).GetProperty("ItemsHost", BindingFlags.Instance | BindingFlags.NonPublic);

    private static Panel GetItemsHost(ItemsControl itemsControl)
    {
        Debug.Assert(itemsControl != null);
        return ItemsHostPropertyInfo.GetValue(itemsControl, null) as Panel;
    }

    #endregion ItemsControl.ItemsHost

    #region Panel.EnsureGenerator

    private static readonly MethodInfo EnsureGeneratorMethodInfo = typeof(Panel).GetMethod("EnsureGenerator", BindingFlags.Instance | BindingFlags.NonPublic);

    private static void CallEnsureGenerator(Panel panel)
    {
        Debug.Assert(panel != null);
        EnsureGeneratorMethodInfo.Invoke(panel, null);
    }

    #endregion Panel.EnsureGenerator

    #region VirtualizingPanel.BringIndexIntoView

    private static readonly MethodInfo BringIndexIntoViewMethodInfo = typeof(VirtualizingPanel).GetMethod("BringIndexIntoView", BindingFlags.Instance | BindingFlags.NonPublic);

    private static void CallBringIndexIntoView(VirtualizingPanel virtualizingPanel, int index)
    {
        Debug.Assert(virtualizingPanel != null);
        BringIndexIntoViewMethodInfo.Invoke(virtualizingPanel, new object[] { index });
    }

    #endregion VirtualizingPanel.BringIndexIntoView

    #endregion Functions to get internal members using reflection
}

With this class, you can write XAML like the following:

使用此类，您可以编写 XAML，如下所示：

<UserControl xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
             xmlns:local="clr-namespace:MyProject">
    <Grid>
        <TreeView ItemsSource="{Binding MyItems}"
                  ScrollViewer.CanContentScroll="True"
                  VirtualizingStackPanel.IsVirtualizing="True"
                  VirtualizingStackPanel.VirtualizationMode="Recycling">
            <i:Interaction.Behaviors>
                <local:NodeTreeSelectionBehavior SelectedItem="{Binding MySelectedItem}" />
            </i:Interaction.Behaviors>
        </TreeView>
    <Grid>
<UserControl>

回答by Heiner

I solved this problem by creating custom controls for TreeView, TreeViewItemand VirtualizingStackPanel. A part of the solution is from http://code.msdn.microsoft.com/Changing-selection-in-a-6a6242c8.

我通过为TreeView、TreeViewItem和创建自定义控件解决了这个问题VirtualizingStackPanel。解决方案的一部分来自http://code.msdn.microsoft.com/Changing-selection-in-a-6a6242c8。

Each TreeItem (bound item) requires to know its parent (enforced by ITreeItem).

每个 TreeItem（绑定项）都需要知道其父项（由 强制执行ITreeItem）。

public interface ITreeItem {
    ITreeItem Parent { get; }
    IList<ITreeItem> Children { get; }
    bool IsSelected { get; set; }
    bool IsExpanded { get; set; }
}

When IsSelectedis set on any TreeItem the view model is notified and raises an event. The corresponding event listener in the view calls BringItemIntoViewon the TreeView.

当IsSelected在任何 TreeItem 上设置时，视图模型会收到通知并引发事件。在查看相应的事件侦听器调用BringItemIntoView上TreeView。

The TreeViewfinds all TreeViewItemson the path to the selected item and brings them into view.

在TreeView查找所有TreeViewItems的路径选择的项目上，并且使他们进入视野。

And here the rest of the code:

其余代码如下：

public class SelectableVirtualizingTreeView : TreeView {
    public SelectableVirtualizingTreeView() {
        VirtualizingStackPanel.SetIsVirtualizing(this, true);
        VirtualizingStackPanel.SetVirtualizationMode(this, VirtualizationMode.Recycling);
        var panelfactory = new FrameworkElementFactory(typeof(SelectableVirtualizingStackPanel));
        panelfactory.SetValue(Panel.IsItemsHostProperty, true);
        var template = new ItemsPanelTemplate { VisualTree = panelfactory };
        ItemsPanel = template;
    }

    public void BringItemIntoView(ITreeItem treeItemViewModel) {
        if (treeItemViewModel == null) {
            return;
        }
        var stack = new Stack<ITreeItem>();
        stack.Push(treeItemViewModel);
        while (treeItemViewModel.Parent != null) {
            stack.Push(treeItemViewModel.Parent);
            treeItemViewModel = treeItemViewModel.Parent;
        }
        ItemsControl containerControl = this;
        while (stack.Count > 0) {
            var viewModel = stack.Pop();
            var treeViewItem = containerControl.ItemContainerGenerator.ContainerFromItem(viewModel);
            var virtualizingPanel = FindVisualChild<SelectableVirtualizingStackPanel>(containerControl);
            if (virtualizingPanel != null) {
                var index = viewModel.Parent != null ? viewModel.Parent.Children.IndexOf(viewModel) : Items.IndexOf(treeViewItem);
                virtualizingPanel.BringIntoView(index);
                Focus();
            }
            containerControl = (ItemsControl)treeViewItem;
        }
    }

    protected override DependencyObject GetContainerForItemOverride() {
        return new SelectableVirtualizingTreeViewItem();
    }

    protected override void PrepareContainerForItemOverride(DependencyObject element, object item) {
        base.PrepareContainerForItemOverride(element, item);
        ((TreeViewItem)element).IsExpanded = true;
    }

    private static T FindVisualChild<T>(Visual visual) where T : Visual {
        for (var i = 0; i < VisualTreeHelper.GetChildrenCount(visual); i++) {
            var child = (Visual)VisualTreeHelper.GetChild(visual, i);
            if (child == null) {
                continue;
            }
            var correctlyTyped = child as T;
            if (correctlyTyped != null) {
                return correctlyTyped;
            }
            var descendent = FindVisualChild<T>(child);
            if (descendent != null) {
                return descendent;
            }
        }
        return null;
    }
}

public class SelectableVirtualizingTreeViewItem : TreeViewItem {
    public SelectableVirtualizingTreeViewItem() {
        var panelfactory = new FrameworkElementFactory(typeof(SelectableVirtualizingStackPanel));
        panelfactory.SetValue(Panel.IsItemsHostProperty, true);
        var template = new ItemsPanelTemplate { VisualTree = panelfactory };
        ItemsPanel = template;
        SetBinding(IsSelectedProperty, new Binding("IsSelected"));
        SetBinding(IsExpandedProperty, new Binding("IsExpanded"));
    }

    protected override DependencyObject GetContainerForItemOverride() {
        return new SelectableVirtualizingTreeViewItem();
    }

    protected override void PrepareContainerForItemOverride(DependencyObject element, object item) {
        base.PrepareContainerForItemOverride(element, item);
        ((TreeViewItem)element).IsExpanded = true;
    }
}

public class SelectableVirtualizingStackPanel : VirtualizingStackPanel {
    public void BringIntoView(int index) {
        if (index < 0) {
            return;
        }
        BringIndexIntoView(index);
    }
}

public abstract class TreeItemBase : ITreeItem {
    protected TreeItemBase() {
        Children = new ObservableCollection<ITreeItem>();
    }

    public ITreeItem Parent { get; protected set; }

    public IList<ITreeItem> Children { get; protected set; }

    public abstract bool IsSelected { get; set; }

    public abstract bool IsExpanded { get; set; }

    public event EventHandler DescendantSelected;

    protected void RaiseDescendantSelected(TreeItemViewModel newItem) {
        if (Parent != null) {
            ((TreeItemViewModel)Parent).RaiseDescendantSelected(newItem);
        } else {
            var handler = DescendantSelected;
            if (handler != null) {
                handler.Invoke(newItem, EventArgs.Empty);
            }
        }
    }
}

public class MainViewModel : INotifyPropertyChanged {
    private TreeItemViewModel _selectedItem;

    public MainViewModel() {
        TreeItemViewModels = new List<TreeItemViewModel> { new TreeItemViewModel { Name = "Item" } };
        for (var i = 0; i < 30; i++) {
            TreeItemViewModels[0].AddChildInitial();
        }
        TreeItemViewModels[0].IsSelected = true;
        TreeItemViewModels[0].DescendantSelected += OnDescendantSelected;
    }

    public event EventHandler DescendantSelected;

    public event PropertyChangedEventHandler PropertyChanged;

    public List<TreeItemViewModel> TreeItemViewModels { get; private set; }

    public TreeItemViewModel SelectedItem {
        get {
            return _selectedItem;
        }
        set {
            if (_selectedItem == value) {
                return;
            }
            _selectedItem = value;
            var handler = PropertyChanged;
            if (handler != null) {
                handler.Invoke(this, new PropertyChangedEventArgs("SelectedItem"));
            }
        }
    }

    private void OnDescendantSelected(object sender, EventArgs eventArgs) {
        var handler = DescendantSelected;
        if (handler != null) {
            handler.Invoke(sender, eventArgs);
        }
    }
}

public partial class MainWindow {
    public MainWindow() {
        InitializeComponent();
        var mainViewModel = (MainViewModel)DataContext;
        mainViewModel.DescendantSelected += OnMainViewModelDescendantSelected;
    }

    private void OnAddButtonClick(object sender, RoutedEventArgs e) {
        var mainViewModel = (MainViewModel)DataContext;
        var treeItemViewModel = mainViewModel.SelectedItem;
        if (treeItemViewModel != null) {
            treeItemViewModel.AddChild();
        }
    }

    private void OnMainViewModelDescendantSelected(object sender, EventArgs eventArgs) {
        _treeView.BringItemIntoView(sender as TreeItemViewModel);
    }

    private void OnTreeViewSelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e) {
        if (e.OldValue == e.NewValue) {
            return;
        }
        var treeView = (TreeView)sender;
        var treeItemviewModel = treeView.SelectedItem as TreeItemViewModel;
        var mainViewModel = (MainViewModel)DataContext;
        mainViewModel.SelectedItem = treeItemviewModel;
    }
}

And in XAML:

在 XAML 中：

<controls:SelectableVirtualizingTreeView x:Name="_treeView" ItemsSource="{Binding TreeItemViewModels}" Margin="8" 
        SelectedItemChanged="OnTreeViewSelectedItemChanged">
    <controls:SelectableVirtualizingTreeView.ItemTemplate>
        <HierarchicalDataTemplate ... />
    </controls:SelectableVirtualizingTreeView.ItemTemplate>
</controls:SelectableVirtualizingTreeView>

回答by Бадалов Бадал

If you used this (https://stackoverflow.com/a/9206992/8559138) decision and sometimes get InvalidOperationException, you can use my fixed decision:

如果您使用了这个 ( https://stackoverflow.com/a/9206992/8559138) 决定并且有时得到 InvalidOperationException，您可以使用我的固定决定：

I update currentParent layout if newParent is null and trying get ContainerFromIndex again.

如果 newParent 为空，我会更新 currentParent 布局并再次尝试获取 ContainerFromIndex。

 newParent = currentParent.ItemContainerGenerator.ContainerFromIndex(index) as TreeViewItem;
 if (newParent == null)
 {
      currentParent.UpdateLayout();
      virtualizingPanel.BringIndexIntoViewPublic(index);
      newParent = currentParent.ItemContainerGenerator.ContainerFromIndex(index) as TreeViewItem;
 }

Full decision:

完整的决定：

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Reflection;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Interactivity;

public class NodeTreeSelectionBehavior : Behavior<TreeView>
{
    public INode SelectedItem
    {
        get { return (INode)GetValue(SelectedItemProperty); }
        set { SetValue(SelectedItemProperty, value); }
    }

    public static readonly DependencyProperty SelectedItemProperty =
        DependencyProperty.Register("SelectedItem", typeof(Node), typeof(NodeTreeSelectionBehavior),
            new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, OnSelectedItemChanged));

    private static void OnSelectedItemChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var newNode = e.NewValue as INode;
        if (newNode == null) return;
        var behavior = (NodeTreeSelectionBehavior)d;
        var tree = behavior.AssociatedObject;

        var nodeDynasty = new List<INode> { newNode };
        var parent = newNode.Parent;
        while (parent != null)
        {
            nodeDynasty.Insert(0, parent);
            parent = parent.Parent;
        }

        var currentParent = tree as ItemsControl;
        foreach (var node in nodeDynasty)
        {
            // first try the easy way
            var newParent = currentParent.ItemContainerGenerator.ContainerFromItem(node) as TreeViewItem;
            var index = 0;
            VirtualizingPanel virtualizingPanel = null;
            if (newParent == null)
            {
                // if this failed, it's probably because of virtualization, and we will have to do it the hard way.
                // this code is influenced by TreeViewItem.ExpandRecursive decompiled code, and the MSDN sample at http://code.msdn.microsoft.com/Changing-selection-in-a-6a6242c8/sourcecode?fileId=18862&pathId=753647475
                // see also the question at http://stackoverflow.com/q/183636/46635
                currentParent.ApplyTemplate();
                var itemsPresenter = (ItemsPresenter)currentParent.Template.FindName("ItemsHost", currentParent);
                if (itemsPresenter != null)
                {
                    itemsPresenter.ApplyTemplate();
                }
                else
                {
                    currentParent.UpdateLayout();
                }

                virtualizingPanel = GetItemsHost(currentParent) as VirtualizingPanel;
                CallEnsureGenerator(virtualizingPanel);
                index = currentParent.Items.IndexOf(node);
                if (index < 0)
                {
                    throw new InvalidOperationException("Node '" + node + "' cannot be fount in container");
                }
                if (virtualizingPanel != null)
                {
                    virtualizingPanel.BringIndexIntoViewPublic(index);
                }
                newParent = currentParent.ItemContainerGenerator.ContainerFromIndex(index) as TreeViewItem;
                if (newParent == null)
                {
                    currentParent.UpdateLayout();
                    virtualizingPanel.BringIndexIntoViewPublic(index);
                    newParent = currentParent.ItemContainerGenerator.ContainerFromIndex(index) as TreeViewItem;
                }
            }

            if (newParent == null)
            {
                  throw new InvalidOperationException("Tree view item cannot be found or created for node '" + node + "'");
            }

            if (node == newNode)
            {
                newParent.IsSelected = true;
                newParent.BringIntoView();
                break;
            }

            newParent.IsExpanded = true;
            currentParent = newParent;
        }
    }

    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.SelectedItemChanged += OnTreeViewSelectedItemChanged;
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();
        AssociatedObject.SelectedItemChanged -= OnTreeViewSelectedItemChanged;
    }

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

    #region Functions to get internal members using reflection

    // Some functionality we need is hidden in internal members, so we use reflection to get them

    #region ItemsControl.ItemsHost

    static readonly PropertyInfo ItemsHostPropertyInfo = typeof(ItemsControl).GetProperty("ItemsHost", BindingFlags.Instance | BindingFlags.NonPublic);

    private static Panel GetItemsHost(ItemsControl itemsControl)
    {
        Debug.Assert(itemsControl != null);
        return ItemsHostPropertyInfo.GetValue(itemsControl, null) as Panel;
    }

    #endregion ItemsControl.ItemsHost

    #region Panel.EnsureGenerator

    private static readonly MethodInfo EnsureGeneratorMethodInfo = typeof(Panel).GetMethod("EnsureGenerator", BindingFlags.Instance | BindingFlags.NonPublic);

    private static void CallEnsureGenerator(Panel panel)
    {
        Debug.Assert(panel != null);
        EnsureGeneratorMethodInfo.Invoke(panel, null);
    }

    #endregion Panel.EnsureGenerator

    #endregion Functions to get internal members using reflection
}

And XAML:

和 XAML：

<UserControl xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
         xmlns:local="clr-namespace:MyProject">
<Grid>
    <TreeView ItemsSource="{Binding MyItems}"
              ScrollViewer.CanContentScroll="True"
              VirtualizingStackPanel.IsVirtualizing="True"
              VirtualizingStackPanel.VirtualizationMode="Recycling">
        <i:Interaction.Behaviors>
            <local:NodeTreeSelectionBehavior SelectedItem="{Binding MySelectedItem}" />
        </i:Interaction.Behaviors>
    </TreeView>
<Grid>

回答by Peregrine

Seeing as there's a new answer recently posted to this question, I'll add my $0.02 into the mix with a MVVM pure solution to this issue.

看到最近针对这个问题发布了一个新答案，我将把我的 0.02 美元添加到这个问题的 MVVM 纯解决方案中。

Given perTreeViewItemViewModelBaseas a base class for treeview item data, you can create a bindable selected item property on the TreeView using an attached property.

将perTreeViewItemViewModelBase作为树视图项数据的基类，您可以使用附加属性在 TreeView 上创建可绑定的选定项属性。

public class perTreeViewHelper : Behavior<TreeView>
{
    public object BoundSelectedItem
    {
        get { return GetValue(BoundSelectedItemProperty); }
        set { SetValue(BoundSelectedItemProperty, value); }
    }

    public static readonly DependencyProperty BoundSelectedItemProperty =
        DependencyProperty.Register("BoundSelectedItem",
            typeof(object),
            typeof(perTreeViewHelper),
            new FrameworkPropertyMetadata(null,
                FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
                OnBoundSelectedItemChanged));

    private static void OnBoundSelectedItemChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
    {
        var item = args.NewValue as perTreeViewItemViewModelBase;

        if (item != null)
            item.IsSelected = true;
    }

    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.SelectedItemChanged += OnTreeViewSelectedItemChanged;
    }

    protected override void OnDetaching()
    {
        AssociatedObject.SelectedItemChanged -= OnTreeViewSelectedItemChanged;
        base.OnDetaching();
    }

    private void OnTreeViewSelectedItemChanged(object obj, RoutedPropertyChangedEventArgs<object> args)
    {
        BoundSelectedItem = args.NewValue;
    }
}

A second helper class handles scrolling TreeViewItems into view. There are two distinct cases

第二个帮助器类处理将 TreeViewItems 滚动到视图中。有两种不同的情况

• when an item is selected
• when an item is expanded, the tree is scrolled to show as many child items as possible

• 当一个项目被选中时
• 当项目展开时，树会滚动以显示尽可能多的子项目

Note the use of dispatcher priority, which ensures that any virtualised items are fully formed before we try to scroll them into view.

请注意调度程序优先级的使用，这可确保在我们尝试将它们滚动到视图之前完全形成任何虚拟化项目。

public static class perTreeViewItemHelper
{
    public static bool GetBringSelectedItemIntoView(TreeViewItem treeViewItem)
    {
        return (bool)treeViewItem.GetValue(BringSelectedItemIntoViewProperty);
    }

    public static void SetBringSelectedItemIntoView(TreeViewItem treeViewItem, bool value)
    {
        treeViewItem.SetValue(BringSelectedItemIntoViewProperty, value);
    }

    public static readonly DependencyProperty BringSelectedItemIntoViewProperty =
        DependencyProperty.RegisterAttached(
            "BringSelectedItemIntoView",
            typeof(bool),
            typeof(perTreeViewItemHelper),
            new UIPropertyMetadata(false, BringSelectedItemIntoViewChanged));

    private static void BringSelectedItemIntoViewChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
    {
        if (!(args.NewValue is bool))
            return;

        var item = obj as TreeViewItem;

        if (item == null)
            return;

        if ((bool)args.NewValue)
            item.Selected += OnTreeViewItemSelected;
        else
            item.Selected -= OnTreeViewItemSelected;
    }

    private static void OnTreeViewItemSelected(object sender, RoutedEventArgs e)
    {
        var item = e.OriginalSource as TreeViewItem;
        item?.BringIntoView();

        // prevent this event bubbling up to any parent nodes
        e.Handled = true;
    }

    public static bool GetBringExpandedChildrenIntoView(TreeViewItem treeViewItem)
    {
        return (bool)treeViewItem.GetValue(BringExpandedChildrenIntoViewProperty);
    }

    public static void SetBringExpandedChildrenIntoView(TreeViewItem treeViewItem, bool value)
    {
        treeViewItem.SetValue(BringExpandedChildrenIntoViewProperty, value);
    }

    public static readonly DependencyProperty BringExpandedChildrenIntoViewProperty =
        DependencyProperty.RegisterAttached(
            "BringExpandedChildrenIntoView",
            typeof(bool),
            typeof(perTreeViewItemHelper),
            new UIPropertyMetadata(false, BringExpandedChildrenIntoViewChanged));

    private static void BringExpandedChildrenIntoViewChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
    {
        if (!(args.NewValue is bool))
            return;

        var item = obj as TreeViewItem;

        if (item == null)
            return;

        if ((bool)args.NewValue)
            item.Expanded += OnTreeViewItemExpanded;
        else
            item.Expanded -= OnTreeViewItemExpanded;
    }

    private static void OnTreeViewItemExpanded(object sender, RoutedEventArgs e)
    {
        var item = e.OriginalSource as TreeViewItem;

        if (item == null)
            return;

        // use DispatcherPriority.ContextIdle, so that we wait for all of the UI elements for any newly visible children to be created

        // first bring the last child into view
        Action action = () =>
        {
            var lastChild = item.ItemContainerGenerator.ContainerFromIndex(item.Items.Count - 1) as TreeViewItem;
            lastChild?.BringIntoView();
        };

        item.Dispatcher.BeginInvoke(action, DispatcherPriority.ContextIdle);

        // then bring the expanded item (back) into view
        action = () => { item.BringIntoView(); };
        item.Dispatcher.BeginInvoke(action, DispatcherPriority.ContextIdle);

        // prevent this event bubbling up to any parent nodes
        e.Handled = true;
    }
}

This helper class can be included in a style for TreeView controls.

这个帮助器类可以包含在 TreeView 控件的样式中。

<Style x:Key="perExpandCollapseToggleStyle" TargetType="ToggleButton">
    <Setter Property="Focusable" Value="False" />
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="ToggleButton">
                <Grid Width="10"
                      Height="10"
                      Background="Transparent">
                    <Path x:Name="ExpanderGlyph"
                          Margin="1"
                          HorizontalAlignment="Left"
                          VerticalAlignment="Center"
                          Data="M 0,3 L 0,5 L 3,5 L 3,8 L 5,8 L 5,5 L 8,5 L 8,3 L 5,3 L 5,0 L 3,0 L 3,3 z"
                          Fill="LightGreen"
                          Stretch="None" />
                </Grid>

                <ControlTemplate.Triggers>
                    <Trigger Property="IsChecked" Value="True">
                        <Setter TargetName="ExpanderGlyph" Property="Data" Value="M 0,0 M 8,8 M 0,3 L 0,5 L 8,5 L 8,3 z" />
                        <Setter TargetName="ExpanderGlyph" Property="Fill" Value="Red" />
                    </Trigger>

                    <Trigger Property="IsEnabled" Value="False">
                        <Setter TargetName="ExpanderGlyph" Property="Fill" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}" />
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

<Style x:Key="perTreeViewItemContainerStyle"
       TargetType="{x:Type TreeViewItem}">

    <!-- Link the properties of perTreeViewItemViewModelBase to the corresponding ones on the TreeViewItem -->
    <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
    <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
    <Setter Property="IsEnabled" Value="{Binding IsEnabled}" />

    <!-- Include the two "Scroll into View" behaviors -->
    <Setter Property="vhelp:perTreeViewItemHelper.BringSelectedItemIntoView" Value="True" />
    <Setter Property="vhelp:perTreeViewItemHelper.BringExpandedChildrenIntoView" Value="True" />

    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type TreeViewItem}">
                <Grid>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="Auto"
                                          MinWidth="14" />
                        <ColumnDefinition Width="*" />
                    </Grid.ColumnDefinitions>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="Auto" />
                        <RowDefinition Height="*" />
                    </Grid.RowDefinitions>
                    <ToggleButton x:Name="Expander"
                                  Grid.Row="0"
                                  Grid.Column="0"
                                  ClickMode="Press"
                                  IsChecked="{Binding Path=IsExpanded, RelativeSource={RelativeSource TemplatedParent}}"
                                  Style="{StaticResource perExpandCollapseToggleStyle}" />

                    <Border x:Name="PART_Border"
                            Grid.Row="0"
                            Grid.Column="1"
                            Padding="{TemplateBinding Padding}"
                            Background="{TemplateBinding Background}"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}">

                        <ContentPresenter x:Name="PART_Header"
                                          Margin="0,2"
                                          HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                                          ContentSource="Header" />

                    </Border>

                    <ItemsPresenter x:Name="ItemsHost"
                                    Grid.Row="1"
                                    Grid.Column="1" />
                </Grid>

                <ControlTemplate.Triggers>
                    <Trigger Property="IsExpanded" Value="false">
                        <Setter TargetName="ItemsHost" Property="Visibility" Value="Collapsed" />
                    </Trigger>

                    <Trigger Property="HasItems" Value="false">
                        <Setter TargetName="Expander" Property="Visibility" Value="Hidden" />
                    </Trigger>

                    <!--  Use the same colors for a selected item, whether the TreeView is focussed or not  -->
                    <Trigger Property="IsSelected" Value="true">
                        <Setter TargetName="PART_Border" Property="Background" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}" />
                        <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.HighlightTextBrushKey}}" />
                    </Trigger>

                    <Trigger Property="IsEnabled" Value="false">
                        <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}" />
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

<Style TargetType="{x:Type TreeView}">
    <Setter Property="ItemContainerStyle" Value="{StaticResource perTreeViewItemContainerStyle}" />
</Style>

I've covered this in more detail in a recent blog post.

我在最近的一篇博文中更详细地介绍了这一点。