c# - WPF TreeView : Why does virtualizing break BringIntoView()?

Question

当您在 WPF 中的 TreeView 上设置 VirtualizingStackPanel.IsVirtualizing="True" 时:

<Window x:Class="WpfApplication2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <TreeView Name="MainTree" VirtualizingStackPanel.IsVirtualizing="True" VirtualizingStackPanel.VirtualizationMode="Recycling"/>
    </Grid>
</Window>

调用 TreeViewItem.BringIntoView() 的以下代码隐藏不起作用:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApplication2
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            TreeViewItem lastTvi2 = null;
            for (int i = 0; i < 100; i++)
            {
                TreeViewItem tvi = new TreeViewItem();
                tvi.Header = "Hello";
                MainTree.Items.Add(tvi);
                for (int j = 0; j < 100; j++)
                {
                    TreeViewItem tvi2 = new TreeViewItem();
                    tvi2.Header = "World";
                    tvi.Items.Add(tvi2);
                    lastTvi2 = tvi2;
                }
            }
            lastTvi2.BringIntoView();
        }
    }
}

然而，当您删除 VirtualizingStackPanel.IsVirtualizing="True" 行时，它会将 lastTvi2 对象(树中的最后一项)带入 View 。为什么这会破坏 TreeViewItem.BringIntoView() 方法？这是正常行为，还是 .NET 错误？

Answer 1

我曾多次偶然发现这个问题，并提出了一个使用标准 treeview 和标准 treeviewitem 对我有用的解决方案

<UserControl
...
<TreeView
    VirtualizingPanel.IsVirtualizing="True"
    VirtualizingPanel.VirtualizationMode="Recycling"/>
...
</UserControl>

public static class TreeViewHelper
{
    private static T FindVisualChild<T>(System.Windows.Media.Visual visual) where T : System.Windows.Media.Visual
    {
        for (int i = 0; i < VisualTreeHelper.GetChildrenCount(visual); i++)
        {
            System.Windows.Media.Visual child = (System.Windows.Media.Visual)VisualTreeHelper.GetChild(visual, i);
            if (child != null)
            {
                T correctlyTyped = child as T;
                if (correctlyTyped != null)
                {
                    return correctlyTyped;
                }

                T descendent = FindVisualChild<T>(child);
                if (descendent != null)
                {
                    return descendent;
                }
            }
        }

        return null;
    }

    public static void BringIntoView(TreeViewItem item)
    {
        ItemsControl parent = item.Parent as ItemsControl;

        if (parent != null)
        {
            System.Windows.Controls.VirtualizingStackPanel itemHost = FindVisualChild<System.Windows.Controls.VirtualizingStackPanel>(parent);

            if (itemHost != null)
            {
                itemHost.BringIndexIntoViewPublic(parent.Items.IndexOf(item));
                item.Focus();
            }
        }
    }
}