WPF ListBox implement autoscroll via behavior extension and SelectedItem

 public class ListBoxAutoScrollBehavior : Behavior<ListBox>
 {
     protected override void OnAttached()
     {
         AssociatedObject.SelectionChanged += AssociatedObject_SelectionChanged;
         base.OnAttached();
     }

     private void AssociatedObject_SelectionChanged(object sender, SelectionChangedEventArgs e)
     {
         var lbx = sender as ListBox;
         if (lbx != null && lbx.SelectedItem != null)
         {
             lbx.ScrollIntoView(lbx.SelectedItem);
         }
     }

     protected override void OnDetaching()
     {
         AssociatedObject.SelectionChanged -= AssociatedObject_SelectionChanged;
         base.OnDetaching();
     }
 }












            <behavior:Interaction.Behaviors>
                <local:ListBoxAutoScrollBehavior/>
            </behavior:Interaction.Behaviors>
            <ListBox.ContextMenu>




private void InitTimer()
{
    System.Timers.Timer tmr = new System.Timers.Timer();
    tmr.Interval = 1000;
    tmr.Elapsed += Tmr_Elapsed;
    tmr.Enabled = true;
}

private void Tmr_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{
    if(++SelectedIdx>=booksCount)
    {
        SelectedIdx = 0;
    }
    SelectedBk = BooksCollection[SelectedIdx];
}

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

//xaml
<Window x:Class="WpfApp38.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"
        WindowState="Maximized"
        xmlns:local="clr-namespace:WpfApp38"
        mc:Ignorable="d"
        Title="{Binding SelectedIdx,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" 
        Height="450" Width="800">
    <Window.Resources>
        <Style TargetType="{x:Type TextBlock}" x:Key="tbkStyle">
            <Setter Property="HorizontalAlignment" Value="Stretch"/>
            <Setter Property="VerticalAlignment" Value="Center"/>
            <Setter Property="FontSize" Value="30"/>
            <Setter Property="Foreground" Value="Red"/>
            <Style.Triggers>
                <Trigger Property="IsMouseOver" Value="True">
                    <Setter Property="FontSize" Value="50"/>
                    <Setter Property="FontWeight" Value="ExtraBold"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    </Window.Resources>
    <Grid>
        <ListBox ItemsSource="{Binding BooksCollection,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
                 SelectedIndex="{Binding SelectedIdx,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
                 SelectedItem="{Binding SelectedBk,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
                 VirtualizingPanel.IsContainerVirtualizable="True"
                 VirtualizingPanel.IsVirtualizing="True"
                 VirtualizingPanel.CacheLength="1"
                 VirtualizingPanel.CacheLengthUnit="Item"
                 >
            <behavior:Interaction.Behaviors>
                <local:ListBoxAutoScrollBehavior/>
            </behavior:Interaction.Behaviors>
            <ListBox.ContextMenu>
                <ContextMenu>
                    <MenuItem Header="Export All" 
                              Command="{Binding ExportAllCommand}"
                              CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type ContextMenu}},Path=PlacementTarget}"/>
                    <MenuItem Header="Mark All Selected"
                              Command="{Binding MarkAllSelected}"
                              CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type ContextMenu}},Path=PlacementTarget}"/>
                </ContextMenu>
            </ListBox.ContextMenu>
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <CheckBox Content="IsSelected"
                                  HorizontalAlignment="Stretch"
                                  VerticalAlignment="Center"
                                  FontSize="30"
                                  IsChecked="{Binding ISSTEM}"
                                  IsThreeState="False"/>
                        <TextBlock Text="{Binding Id}"
                                   Style="{StaticResource tbkStyle}"/>
                        <TextBlock Text="{Binding ISBN}" 
                                   Style="{StaticResource tbkStyle}"
                                   />
                        <Border Width="500" Height="500"
                                BorderThickness="3"
                                BorderBrush="Black"
                                >
                            <Border.Background>
                                <ImageBrush ImageSource="{Binding ImgSource}"
                                            RenderOptions.BitmapScalingMode="Fant"
                                            RenderOptions.EdgeMode="Aliased"/>
                            </Border.Background>
                        </Border>
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>            
        </ListBox>
    </Grid>
</Window>




//cs
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Data.SqlTypes;
using System.IO;
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;
using Microsoft.Xaml.Behaviors;
using Newtonsoft.Json;

namespace WpfApp38
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            var vm = new BookVM();
            this.DataContext = vm;
        }
    }

    public class BookVM : INotifyPropertyChanged
    {
        public BookVM()
        {
            InitData();
            InitCommands();            
        }

        private void InitTimer()
        {
            System.Timers.Timer tmr = new System.Timers.Timer();
            tmr.Interval = 1000;
            tmr.Elapsed += Tmr_Elapsed;
            tmr.Enabled = true;
        }

        private void Tmr_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            if(++SelectedIdx>=booksCount)
            {
                SelectedIdx = 0;
            }
            SelectedBk = BooksCollection[SelectedIdx];
        }

        private void InitCommands()
        {
            ExportAllCommand = new DelCommand(ExportAllCommandExecuted);
            MarkAllSelected = new DelCommand(MarkAllSelectedExecuted);
        }

        private void MarkAllSelectedExecuted(object obj)
        {
            var books = ((System.Collections.IList)(obj as ListBox).ItemsSource)?.Cast<Book>()?.ToList();
            if (books != null && books.Any())
            {
                booksCount = books.Count;
                for (int i = 0; i < booksCount; i++)
                {
                    books[i].ISSTEM = true;
                }
                MessageBox.Show("Mark all as Selected!");
            }
        }

        private void ExportAllCommandExecuted(object obj)
        {
            var books = ((System.Collections.IList)(obj as ListBox))?.Cast<Book>()?.ToList();
            if (books != null && books.Any())
            {
                string jsonStr = JsonConvert.SerializeObject(books, Formatting.Indented);
                string jsonFile = $"{DateTime.Now.ToString("yyyyMMddHHmmssffff")}json.json";
                File.WriteAllText(jsonFile, jsonStr);
                MessageBox.Show($"Exported in {jsonFile}", "Export");
            }
        }

        private void InitData()
        {
            var imgs = Directory.GetFiles(@"../../Images");

            if (imgs != null && imgs.Any())
            {
                int imgsCount = imgs.Count();
                BooksCollection = new ObservableCollection<Book>();
                for (int i = 0; i < 100000; i++)
                {
                    BooksCollection.Add(new Book()
                    {
                        Id = i + 1,
                        ISBN = $"ISBN_{i + 1}",
                        ISSTEM = (i % 5 == 0) ? true : false,
                        ImgSource = GetImgSourceViaUrl(imgs[i % imgsCount])
                    });
                }
                booksCount=BooksCollection.Count;
            }
            InitTimer();
        }

        private ImageSource GetImgSourceViaUrl(string url)
        {
            BitmapImage bmi = new BitmapImage();
            bmi.BeginInit();
            bmi.UriSource = new Uri(url, UriKind.RelativeOrAbsolute);
            bmi.EndInit();
            if (bmi.CanFreeze)
            {
                bmi.Freeze();
            }
            return bmi;
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged(string propertyName)
        {
            var handler = PropertyChanged;
            if (handler != null)
            {
                handler?.Invoke(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        private ObservableCollection<Book> booksCollection;
        public ObservableCollection<Book> BooksCollection
        {
            get
            {
                return booksCollection;
            }
            set
            {
                if (value != booksCollection)
                {
                    booksCollection = value;
                    OnPropertyChanged(nameof(BooksCollection));
                }
            }
        }

        private int selectedIdx;
        public int SelectedIdx
        {
            get
            {
                return selectedIdx;
            }
            set
            {
                if (value != selectedIdx)
                {
                    selectedIdx = value;
                    OnPropertyChanged(nameof(SelectedIdx));
                }
            }
        }

        private Book selectedBk;
        public Book SelectedBk
        {
            get
            {
                return selectedBk;
            }
            set
            {
                if(value!=selectedBk)
                {
                    selectedBk = value;
                    OnPropertyChanged(nameof(SelectedBk));
                }
            }
        }

        private int booksCount { get; set; } = 0;

        public DelCommand ExportAllCommand { get; set; }
        public DelCommand MarkAllSelected { get; set; }
    }

    public class ListBoxAutoScrollBehavior : Behavior<ListBox>
    {
        protected override void OnAttached()
        {
            AssociatedObject.SelectionChanged += AssociatedObject_SelectionChanged;
            base.OnAttached();
        }

        private void AssociatedObject_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            var lbx = sender as ListBox;
            if (lbx != null && lbx.SelectedItem != null)
            {
                lbx.ScrollIntoView(lbx.SelectedItem);
            }
        }

        protected override void OnDetaching()
        {
            AssociatedObject.SelectionChanged -= AssociatedObject_SelectionChanged;
            base.OnDetaching();
        }
    }

    public class Book
    {
        public int Id { get; set; }
        public bool ISSTEM { get; set; }
        public string ISBN { get; set; }
        public ImageSource ImgSource { get; set; }
    }

    public class DelCommand : ICommand
    {
        private Action<object> execute;
        private Predicate<object> canExecute;

        public DelCommand(Action<Object> executeValue, Predicate<object> canExecuteValue = null)
        {
            execute = executeValue;
            canExecute = canExecuteValue;
        }

        public event EventHandler CanExecuteChanged
        {
            add
            {
                CommandManager.RequerySuggested += value;
            }
            remove
            {
                CommandManager.RequerySuggested -= value;
            }
        }

        public bool CanExecute(object parameter)
        {
            if (canExecute == null)
            {
                return true;
            }
            return canExecute(parameter);
        }

        public void Execute(object parameter)
        {
            execute(parameter);
        }
    }
}