问使用WPF在虚拟化TreeView中选择节点
EN

Stack Overflow用户

提问于 2008-10-08 16:25:27

回答 6查看 13K关注 0票数 19

有没有办法在虚拟化TreeView中手动选择一个节点，然后将其带到视图中？

我在TreeView中使用的数据模型是基于VM-M-V模型实现的。每个TreeViewItem的IsSelected属性都绑定到ViewModel中相应的属性。我还为TreeView的ItemSelected事件创建了一个侦听器，其中我为选定的TreeViewItem调用BringIntoView()。

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滚动足够多，然后当事件最终被引发时，它会“神奇地”跳到所选的节点。

我真的很想使用虚拟化，因为我的树中有数千个节点，而且在启用虚拟化后，我已经看到了令人印象深刻的性能改进。

wpf

mvvm

treeview

回答 6

Stack Overflow用户

发布于 2012-02-09 15:30:53

Estifanos Kidane给出的链接被打破了。他可能指的是the "Changing selection in a virtualized TreeView" MSDN sample。但是，这个示例展示了如何选择树中的节点，但使用的是代码隐藏而不是MVVM和绑定，因此当绑定的SelectedItemChanged event发生更改时，它也不会处理丢失的SelectedItem。

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)，以确保在树中实际选择了新值。

下面是我编写的处理它的代码。假设您的数据项是具有Parent属性的Node类型：

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

我写了下面的behavior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
}

使用此类，您可以编写如下所示的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>
<UserControl>

票数 17

Stack Overflow用户

发布于 2013-07-26 22:09:37

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

每个TreeItem (绑定项)都需要知道它的父项(由ITreeItem强制执行)。

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

当在任何TreeItem上设置了IsSelected时，视图模型都会收到通知并引发一个事件。视图中相应的事件侦听器在TreeView上调用BringItemIntoView。

TreeView查找所选项目路径上的所有TreeViewItems，并将它们带到视图中。

下面是代码的其余部分：

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;
    }
}

在XAML中：

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

票数 2

Stack Overflow用户

发布于 2009-11-12 23:00:03

我使用了一个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

}

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

票数 1

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/183636

复制

相似问题

问使用WPF在虚拟化TreeView中选择节点
EN

回答 6

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问使用WPF在虚拟化TreeView中选择节点EN

回答 6

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问使用WPF在虚拟化TreeView中选择节点
EN