Выбор узла в виртуализированном TreeView с WPF

Question

Есть ли способ вручную выбрать узел в виртуализации TreeView и затем отобразить его?

Модель данных, которую я использую с моим TreeView, реализована на основе модели VM-M-V. Каждое свойство IsViewetem TreeViewItem привязано к соответствующему свойству в ViewModel. Я также создал слушатель для события ItemSelected TreeView, где я вызываю BringIntoView () для выбранного TreeViewItem.

Проблема этого подхода заключается в том, что событие ItemSelected не будет вызываться до тех пор, пока не будет создан фактический TreeViewItem. Таким образом, с включенной виртуализацией выбор узла ничего не изменит, пока TreeView не будет прокручен достаточно, а затем он «магически» перейдет к выбранному узлу, когда событие будет наконец инициировано.

Мне бы очень хотелось использовать виртуализацию, потому что в моем дереве тысячи узлов, и я уже видел впечатляющие улучшения производительности, когда виртуализация была включена.

Answer 1

Ссылка, которую дал Эстифанос Кидане, не работает. Вероятно, он имел в виду образец MSDN "Изменение выделения в виртуализированном TreeView" . однако в этом примере показано, как выбрать узел в дереве, но с использованием выделенного кода, а не MVVM и привязки, поэтому он также не обрабатывает отсутствующее событие SelectedItemChanged при изменении привязанного SelectedItem.

Единственное решение, которое я могу придумать, - это сломать шаблон MVVM, и, когда свойство ViewModel, связанное со свойством SelectedItem, изменится, получите View и вызовите метод code-behind (аналогично примеру MSDN), который гарантирует новое значение фактически выбрано в дереве.

Вот код, который я написал, чтобы справиться с этим. Предположим, что ваши элементы данных имеют тип Node, который имеет свойство Parent:

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

Я написал следующий класс поведения:

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
}

С помощью этого класса вы можете написать XAML следующим образом:

<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>

Answer 2

Я решил эту проблему, создав пользовательские элементы управления для TreeView, TreeViewItem и VirtualizingStackPanel. Часть решения от http://code.msdn.microsoft.com/Changing-selection-in-a-6a6242c8.

Каждый TreeItem (связанный элемент) должен знать своего родителя (принудительно ITreeItem).

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

Когда IsSelected установлен на любом TreeItem, модель представления уведомляется и вызывает событие. Соответствующий прослушиватель событий в представлении вызывает BringItemIntoView для TreeView.

TreeView находит все TreeViewItems на пути к выбранному элементу и отображает их.

А вот и остальной код:

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;
    }
}

И в XAML:

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

Answer 3

Если вы использовали это (https://stackoverflow.com/a/9206992/8559138) решение и иногда получали InvalidOperationException, вы можете использовать мое фиксированное решение:

Я обновляю макет currentParent, если newParent равен null, и пытаюсь снова получить ContainerFromIndex.

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

Полное решение:

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
}

И 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>

Answer 4

Я использовал прикрепленное свойство, чтобы решить эту проблему.

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

}

И в моем стиле XAML для TreeViewItem я просто установил для свойства значение true

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

НТН

Answer 5

Поскольку на этот вопрос недавно был опубликован новый ответ, я добавлю свои 0,02 долл. США в смесь с чистым решением MVVM для этой проблемы.

Учитывая perTreeViewItemViewModelBase в качестве базового класса для данных элемента дерева, вы можете создать привязываемое свойство выбранного элемента в TreeView, используя присоединенное свойство.

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;
    }
}

Второй вспомогательный класс обрабатывает прокрутку TreeViewItems в представлении. Есть два разных случая

• при выборе элемента
• при расширении элемента дерево прокручивается, чтобы показать максимально возможное количество дочерних элементов

Обратите внимание на использование приоритета диспетчера, который гарантирует, что любые виртуализированные элементы полностью сформированы, прежде чем мы попытаемся прокрутить их в поле зрения.

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;
    }
}

Этот вспомогательный класс может быть включен в стиль для элементов управления TreeView.

<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>

Я рассмотрел это более подробно в недавнем блоге .

Answer 6

Вот пример, взятый из MSDN Вопрос public void ScrollToItem (int index)

    {

        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);

    }