WPF two listbox scroll syncchronously via behavior

Install-Package Microsoft.Xamls.Behavior.WPF

 public class ListBoxSyncScrollBehavior : Behavior<ListBox>
 {
     static Dictionary<string, ScrollViewer> scrollViewerCache = new Dictionary<string, ScrollViewer>();

     public ListBox SourceObj
     {
         get { return (ListBox)GetValue(SourceObjProperty); }
         set { SetValue(SourceObjProperty, value); }
     }

     // Using a DependencyProperty as the backing store for SourceObj.  This enables animation, styling, binding, etc...
     public static readonly DependencyProperty SourceObjProperty =
         DependencyProperty.Register(
             nameof(SourceObj),
             typeof(ListBox),
             typeof(ListBoxSyncScrollBehavior),
             new PropertyMetadata(null));



     protected override void OnAttached()
     {
         base.OnAttached();

         AssociatedObject.Loaded += AssociatedObject_Loaded;
         AssociatedObject.Unloaded += AssociatedObject_Unloaded;
     }

     private void AssociatedObject_Unloaded(object sender, RoutedEventArgs e)
     {
         scrollViewerCache.Clear();
     }

     private void AssociatedObject_Loaded(object sender, RoutedEventArgs e)
     {
         if (!scrollViewerCache.ContainsKey(AssociatedObject.Name))
         {
             var scrollViewer = GetScrollViewer(AssociatedObject);
             if (scrollViewer != null)
             {
                 scrollViewer.Name = AssociatedObject.Name;
                 scrollViewerCache.Add(AssociatedObject.Name, scrollViewer);
                 scrollViewer.ScrollChanged += ScrollViewer_ScrollChanged;
             }
         }
     }

     private void ScrollViewer_ScrollChanged(object sender, ScrollChangedEventArgs e)
     {
         var srcScrollViewer = sender as ScrollViewer;
         if (srcScrollViewer != null)
         {
             foreach (var de in scrollViewerCache)
             {
                 if (de.Key != srcScrollViewer.Name)
                 {
                     var targetScrollViewer = scrollViewerCache[de.Key] as ScrollViewer;
                     if (targetScrollViewer != null)
                     {
                         targetScrollViewer.ScrollToVerticalOffset(srcScrollViewer.VerticalOffset);
                         targetScrollViewer.ScrollToHorizontalOffset(srcScrollViewer.HorizontalOffset);
                     }
                 }
             }
         }
     }

     protected override void OnDetaching()
     {
         base.OnDetaching();
     }


     private ScrollViewer GetScrollViewer(DependencyObject dpObj)
     {
         int cnt = VisualTreeHelper.GetChildrenCount(dpObj);
         for (int i = 0; i < cnt; i++)
         {
             var obj = VisualTreeHelper.GetChild(dpObj, i);
             if (obj is ScrollViewer scrollViewer)
             {
                 return scrollViewer;
             }
             var result = GetScrollViewer(obj) as ScrollViewer;
             if (result != null)
             {
                 return result;
             }
         }
         return null;
     }
 }

 

 

//WPF
<Window x:Class="WpfApp2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:behavior="http://schemas.microsoft.com/xaml/behaviors"
        xmlns:local="clr-namespace:WpfApp2"
        mc:Ignorable="d"
        Title="{Binding MainTitle}" WindowState="Maximized">
    <Window.DataContext>
        <local:MainVM/>
    </Window.DataContext>
    <Window.Resources>
        <Style TargetType="TextBlock" x:Key="TbkStyle">
            <Setter Property="FontSize" Value="30"/>
            <Style.Triggers>
                <Trigger Property="IsMouseOver" Value="True">
                    <Setter Property="Foreground" Value="Red"/>
                    <Setter Property="FontWeight" Value="ExtraBold"/>
                </Trigger>
            </Style.Triggers>
        </Style>

        <DataTemplate DataType="{x:Type local:Book}"
                      x:Key="BookDataTemplate">
            <Grid MinHeight="150" Margin="10,50,10,50">
                <Grid.Resources>
                    <Style TargetType="TextBlock" BasedOn="{StaticResource TbkStyle}"/>
                </Grid.Resources>
                <Grid.RowDefinitions>
                    <RowDefinition/>
                    <RowDefinition/>
                    <RowDefinition/>
                    <RowDefinition/>
                </Grid.RowDefinitions>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition/>
                    <ColumnDefinition/>
                    <ColumnDefinition/>
                </Grid.ColumnDefinitions>
                <TextBlock Text="{Binding Id}" Grid.Row="0" Grid.Column="0"/>
                <TextBlock Text="{Binding Name}" Grid.Row="0" Grid.Column="1"/>
                <TextBlock Text="{Binding Author}" Grid.Row="0" Grid.Column="2"/>
                <TextBlock Text="{Binding CategoryName}" Grid.Row="1" Grid.Column="0"/>
                <TextBlock Text="{Binding Comment}" Grid.Row="1" Grid.Column="1"/>
                <TextBlock Text="{Binding Content}" Grid.Row="1" Grid.Column="2"/>
                <TextBlock Text="{Binding Summary}" Grid.Row="2" Grid.Column="0"/>
                <TextBlock Text="{Binding Title}" Grid.Row="2" Grid.Column="1"/>
                <TextBlock Text="{Binding Topic}" Grid.Row="2" Grid.Column="2"/>
                <TextBlock Text="{Binding ISBN}" Grid.Row="3" Grid.Column="0" Grid.ColumnSpan="3"/>
            </Grid>
        </DataTemplate>

    </Window.Resources>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <!--<ItemsControl  Grid.Column="0" 
                 BorderBrush="LightBlue"
                 BorderThickness="5"
                 ItemsSource="{Binding BksCollection}"
                 VirtualizingPanel.IsVirtualizing="True"
                 VirtualizingPanel.VirtualizationMode="Recycling"
                 VirtualizingPanel.CacheLengthUnit="Item"
                 VirtualizingPanel.CacheLength="5,5">
            <ItemsControl.Template>
                <ControlTemplate TargetType="ItemsControl">
                    <Border>
                        <ScrollViewer>
                            <ItemsPresenter/>
                        </ScrollViewer>
                    </Border>
                </ControlTemplate>
            </ItemsControl.Template>
            <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                    <VirtualizingStackPanel IsItemsHost="True"/>
                </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>

            <ItemsControl.ItemTemplate>
                <StaticResource ResourceKey="BookDataTemplate"/>
            </ItemsControl.ItemTemplate>
        </ItemsControl>-->

        <ListBox Grid.Column="0"
                 x:Name="lbx1"
                 BorderBrush="LightCyan"
                 BorderThickness="5"
                 ItemsSource="{Binding BksCollection}"                 
                 VirtualizingPanel.IsVirtualizing="True"
                 VirtualizingPanel.VirtualizationMode="Recycling"
                 VirtualizingPanel.CacheLength="5,5"
                 VirtualizingPanel.CacheLengthUnit="Item"
                 ItemTemplate="{StaticResource BookDataTemplate}"
                 >
            <behavior:Interaction.Behaviors>
                <local:ListBoxSyncScrollBehavior SourceObj="{Binding ElementName=lbx1}"/>
            </behavior:Interaction.Behaviors>
        </ListBox>

        <ListBox Grid.Column="1" 
                 x:Name="lbx2"
                 BorderBrush="LightCyan"
                 BorderThickness="5"
                 ItemsSource="{Binding BksCollection}"                 
                 VirtualizingPanel.IsVirtualizing="True"
                 VirtualizingPanel.VirtualizationMode="Recycling"
                 VirtualizingPanel.CacheLength="5,5"
                 VirtualizingPanel.CacheLengthUnit="Item"
                 ItemTemplate="{StaticResource BookDataTemplate}">
            <behavior:Interaction.Behaviors>
                <local:ListBoxSyncScrollBehavior SourceObj="{Binding ElementName=lbx2}"/>
            </behavior:Interaction.Behaviors>
        </ListBox>
    </Grid>


</Window>

//cs
using System.Collections;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Net.Http;
using System.Runtime.CompilerServices;
using System.Text;
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;
using Microsoft.Xaml.Behaviors;
using Newtonsoft.Json;

namespace WpfApp2
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }

    public class MainVM : INotifyPropertyChanged
    {
        private static HttpClient client = new HttpClient()
        {
            Timeout = TimeSpan.FromHours(1)
        };

        private string url = "http://localhost:5000/api/book/getbooks/";
        private bool isLoading = false;

        public MainVM()
        {
            if (!DesignerProperties.GetIsInDesignMode(new DependencyObject()))
            {
                _ = LoadDataAsync(1000000);
            }
        }

        private async Task LoadDataAsync(int cnt = 1000000)
        {
            if (isLoading)
            {
                return;
            }
            isLoading = true;

            try
            {
                MainTitle = $"{DateTime.Now},loading...";
                string jsonStr = await client.GetStringAsync($"{url}{cnt}");
                List<Book> bks = JsonConvert.DeserializeObject<List<Book>>(jsonStr);
                if (bks != null && bks.Any())
                {
                    BksCollection = new ObservableCollection<Book>(bks);
                    MainTitle = $"{DateTime.Now},loaded {BksCollection.Count} items,FirstId:{BksCollection.FirstOrDefault()?.Id}," +
                        $"LastId:{BksCollection.LastOrDefault()?.Id}";
                    System.Diagnostics.Debug.WriteLine(MainTitle);
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex?.Message);
            }
            finally
            {
                isLoading = false;
            }
        }

        private ObservableCollection<Book> bksCollection;
        public ObservableCollection<Book> BksCollection
        {
            get
            {
                return bksCollection;
            }
            set
            {
                if (value != bksCollection)
                {
                    bksCollection = value;
                    OnPropertyChanged();
                }
            }
        }

        private string mainTitle = $"{DateTime.Now}";
        public string MainTitle
        {
            get
            {
                return mainTitle;
            }
            set
            {
                if (value != mainTitle)
                {
                    mainTitle = value;
                    OnPropertyChanged();
                }
            }
        }

        public event PropertyChangedEventHandler? PropertyChanged;
        private void OnPropertyChanged([CallerMemberName] string propName = "")
        {
            var handler = Volatile.Read(ref PropertyChanged);
            if (handler == null)
            {
                return;
            }
            handler(this, new PropertyChangedEventArgs(propName));
        }
    }

    public class Book
    {
        public long Id { get; set; }
        public string Name { get; set; }
        public string Author { get; set; }
        public string CategoryName { get; set; }
        public string Comment { get; set; }
        public string Content { get; set; }
        public string ISBN { get; set; }
        public string Summary { get; set; }
        public string Title { get; set; }
        public string Topic { get; set; }
    }

    public class ListBoxSyncScrollBehavior : Behavior<ListBox>
    {
        static Dictionary<string, ScrollViewer> scrollViewerCache = new Dictionary<string, ScrollViewer>();

        public ListBox SourceObj
        {
            get { return (ListBox)GetValue(SourceObjProperty); }
            set { SetValue(SourceObjProperty, value); }
        }

        // Using a DependencyProperty as the backing store for SourceObj.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty SourceObjProperty =
            DependencyProperty.Register(
                nameof(SourceObj),
                typeof(ListBox),
                typeof(ListBoxSyncScrollBehavior),
                new PropertyMetadata(null));



        protected override void OnAttached()
        {
            base.OnAttached();

            AssociatedObject.Loaded += AssociatedObject_Loaded;
            AssociatedObject.Unloaded += AssociatedObject_Unloaded;
        }

        private void AssociatedObject_Unloaded(object sender, RoutedEventArgs e)
        {
            scrollViewerCache.Clear();
        }

        private void AssociatedObject_Loaded(object sender, RoutedEventArgs e)
        {
            if (!scrollViewerCache.ContainsKey(AssociatedObject.Name))
            {
                var scrollViewer = GetScrollViewer(AssociatedObject);
                if (scrollViewer != null)
                {
                    scrollViewer.Name = AssociatedObject.Name;
                    scrollViewerCache.Add(AssociatedObject.Name, scrollViewer);
                    scrollViewer.ScrollChanged += ScrollViewer_ScrollChanged;
                }
            }
        }

        private void ScrollViewer_ScrollChanged(object sender, ScrollChangedEventArgs e)
        {
            var srcScrollViewer = sender as ScrollViewer;
            if (srcScrollViewer != null)
            {
                foreach (var de in scrollViewerCache)
                {
                    if (de.Key != srcScrollViewer.Name)
                    {
                        var targetScrollViewer = scrollViewerCache[de.Key] as ScrollViewer;
                        if (targetScrollViewer != null)
                        {
                            targetScrollViewer.ScrollToVerticalOffset(srcScrollViewer.VerticalOffset);
                            targetScrollViewer.ScrollToHorizontalOffset(srcScrollViewer.HorizontalOffset);
                        }
                    }
                }
            }
        }

        protected override void OnDetaching()
        {
            base.OnDetaching();
        }


        private ScrollViewer GetScrollViewer(DependencyObject dpObj)
        {
            int cnt = VisualTreeHelper.GetChildrenCount(dpObj);
            for (int i = 0; i < cnt; i++)
            {
                var obj = VisualTreeHelper.GetChild(dpObj, i);
                if (obj is ScrollViewer scrollViewer)
                {
                    return scrollViewer;
                }
                var result = GetScrollViewer(obj) as ScrollViewer;
                if (result != null)
                {
                    return result;
                }
            }
            return null;
        }
    }
}