WPF ListBox ScrollViewer get scrolled current item actual vertical position in the whole scrollview of listbox via mvvm

 <i:Interaction.Triggers>
     <i:EventTrigger EventName="PreviewMouseWheel">
         <i:InvokeCommandAction Command="{Binding MouseWheelCommand}"
                            CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type ListBox}}}"
                            />
     </i:EventTrigger>
 </i:Interaction.Triggers>


double perItemHeight = 0.0d;
ListBoxItem firstItem;
private void MouseWheelCommandExecuted(object? obj)
{
    var lbx = obj as ListBox;
    if (lbx == null)
    {
        return;
    }
    if (firstItem == null)
    {
        firstItem = lbx.ItemContainerGenerator.ContainerFromIndex(0) as ListBoxItem;
        if (firstItem != null)
        {
            perItemHeight = firstItem.ActualHeight;
        }
    }

    var scrollViewer = FindVisualChild<ScrollViewer>(lbx);
    if (scrollViewer != null)
    {
        scrollViewer.ScrollChanged += ScrollViewer_ScrollChanged;
        //double viewportHeight = scrollViewer.ViewportHeight;
        //double extentHeight = scrollViewer.ExtentHeight;
        //double verticalOffset = scrollViewer.VerticalOffset;

        //double currentVerticalOffset = scrollViewer.VerticalOffset;
        //double maxVerticalOffset = scrollViewer.ExtentHeight - scrollViewer.ViewportHeight;

        //// Display or use the current scroll position
        //Debug.WriteLine($"Current Y position: {currentVerticalOffset}");
        //Debug.WriteLine($"Max Y position: {maxVerticalOffset}");

        //// You can also calculate percentage scrolled
        //double percentageScrolled = currentVerticalOffset / maxVerticalOffset;
        //Debug.WriteLine($"Percentage scrolled: {percentageScrolled:P}");
    }

}

private void ScrollViewer_ScrollChanged(object sender, ScrollChangedEventArgs e)
{
    PosY = (e.VerticalOffset + 1) * perItemHeight;
}

public static T FindVisualChild<T>(DependencyObject obj) where T : DependencyObject
{
    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
    {
        DependencyObject child = VisualTreeHelper.GetChild(obj, i);
        if (child != null && child is T)
        {
            return (T)child;
        }
        else
        {
            T childOfChild = FindVisualChild<T>(child);
            if (childOfChild != null)
            {
                return childOfChild;
            }
        }
    }
    return null;
}

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

install-package  Microsoft.Xaml.Behaviors.Wpf

 

//xaml
<Window x:Class="WpfApp45.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:i="http://schemas.microsoft.com/xaml/behaviors"
        WindowState="Maximized"
        xmlns:local="clr-namespace:WpfApp45"
        mc:Ignorable="d"
        Title="{Binding PosY,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
    Height="450" Width="800">
    <Grid Background="#000000">
        <ListBox x:Name="lbx"
             Focusable="True"
             SelectedIndex="{Binding SelectedIdx,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
             ItemsSource="{Binding BooksCollection,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
             SelectionMode="Extended">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="PreviewMouseWheel">
                    <i:InvokeCommandAction Command="{Binding MouseWheelCommand}"
                                       CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type ListBox}}}"
                                       />
                </i:EventTrigger>
            </i:Interaction.Triggers>
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Grid>
                        <Grid.Background>
                            <ImageBrush ImageSource="{Binding ImgSource}"/>
                        </Grid.Background>
                        <Grid.Resources>
                            <Style TargetType="{x:Type Grid}">
                                <Setter Property="Height" Value="300"/>
                            </Style>
                            <Style TargetType="{x:Type TextBlock}">
                                <Setter Property="FontSize" Value="30"/>
                                <Setter Property="Foreground" Value="Black"/>
                                <Style.Triggers>
                                    <Trigger Property="IsMouseOver" Value="True">
                                        <Setter Property="FontSize" Value="80"/>
                                        <Setter Property="Foreground" Value="Red"/>
                                    </Trigger>
                                </Style.Triggers>
                            </Style>
                        </Grid.Resources>
                        <Grid.RowDefinitions>
                            <RowDefinition/>
                            <RowDefinition/>
                        </Grid.RowDefinitions>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition/>
                            <ColumnDefinition/>
                            <ColumnDefinition/>
                        </Grid.ColumnDefinitions>
                        <TextBlock Grid.Row="0" Grid.Column="0" Text="{Binding Id}"/>
                        <TextBlock Grid.Row="0" Grid.Column="1" Text="{Binding Name}"/>
                        <TextBlock Grid.Row="0" Grid.Column="2" Text="{Binding Title}"/>
                        <TextBlock Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="3" Text="{Binding ISBN}"/>
                    </Grid>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</Window>



//cs
using Microsoft.Win32;
using System.Collections;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.IO;
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 System.Xml;

namespace WpfApp45
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            var vm = new MainVM();
            this.DataContext = vm;
        }
    }


    public class MainVM : INotifyPropertyChanged
    {
        public MainVM()
        {
            InitBooksCollection();
            MouseWheelCommand = new DelCommand(MouseWheelCommandExecuted);
        }

        double perItemHeight = 0.0d;
        ListBoxItem firstItem;
        private void MouseWheelCommandExecuted(object? obj)
        {
            var lbx = obj as ListBox;
            if (lbx == null)
            {
                return;
            }
            if (firstItem == null)
            {
                firstItem = lbx.ItemContainerGenerator.ContainerFromIndex(0) as ListBoxItem;
                if (firstItem != null)
                {
                    perItemHeight = firstItem.ActualHeight;
                }
            }

            var scrollViewer = FindVisualChild<ScrollViewer>(lbx);
            if (scrollViewer != null)
            {
                scrollViewer.ScrollChanged += ScrollViewer_ScrollChanged;
                //double viewportHeight = scrollViewer.ViewportHeight;
                //double extentHeight = scrollViewer.ExtentHeight;
                //double verticalOffset = scrollViewer.VerticalOffset;

                //double currentVerticalOffset = scrollViewer.VerticalOffset;
                //double maxVerticalOffset = scrollViewer.ExtentHeight - scrollViewer.ViewportHeight;

                //// Display or use the current scroll position
                //Debug.WriteLine($"Current Y position: {currentVerticalOffset}");
                //Debug.WriteLine($"Max Y position: {maxVerticalOffset}");

                //// You can also calculate percentage scrolled
                //double percentageScrolled = currentVerticalOffset / maxVerticalOffset;
                //Debug.WriteLine($"Percentage scrolled: {percentageScrolled:P}");
            }

        }

        private void ScrollViewer_ScrollChanged(object sender, ScrollChangedEventArgs e)
        {
            PosY = (e.VerticalOffset + 1) * perItemHeight;
        }

        public static T FindVisualChild<T>(DependencyObject obj) where T : DependencyObject
        {
            for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
            {
                DependencyObject child = VisualTreeHelper.GetChild(obj, i);
                if (child != null && child is T)
                {
                    return (T)child;
                }
                else
                {
                    T childOfChild = FindVisualChild<T>(child);
                    if (childOfChild != null)
                    {
                        return childOfChild;
                    }
                }
            }
            return null;
        }       

        private void InitBooksCollection()
        {
            BooksCollection = new ObservableCollection<Book>();
            var dir = @"../../../Images";
            if (Directory.Exists(dir))
            {
                var imgs = Directory.GetFiles(dir);
                int imgsCount = imgs.Count();
                for (int i = 0; i < 1000; i++)
                {
                    BooksCollection.Add(new Book()
                    {
                        Id = i + 1,
                        Name = $"Name_{i + 1}",
                        Title = $"Title_{i + 1}",
                        ISBN = $"{Guid.NewGuid().ToString("N")}",
                        ImgSource = GetImgSourceVirUrl(imgs[i % imgsCount]),
                    });
                }
            }
        }

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

        public event PropertyChangedEventHandler? PropertyChanged;
        public void OnPropertyChanged([CallerMemberName] 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 ?? (booksCollection = new ObservableCollection<Book>());
            }
            set
            {
                if (value != null)
                {
                    booksCollection = value;
                    OnPropertyChanged();
                }
            }
        }

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

        private bool isSelected;
        public bool IsSelected
        {
            get
            {
                return isSelected;
            }
            set
            {
                if (value != isSelected)
                {
                    isSelected = value;
                    OnPropertyChanged();
                }
            }
        }

        private IList _selectedItems;
        public IList SelectedItems
        {
            get => _selectedItems;
            set { _selectedItems = value; OnPropertyChanged(); }
        }

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

        private double posY;
        public double PosY
        {
            get
            {
                return posY;
            }
            set
            {
                if (value != posY)
                {
                    posY = value;
                    OnPropertyChanged();
                }
            }
        }
        public ICommand MouseWheelCommand { get; set; }
    }

    public class DelCommand : ICommand
    {
        private Action<object?> execcute;
        private Predicate<object?> canExecute;
        public DelCommand(Action<object?> execcuteValue, Predicate<object?> canExecuteValue = null)
        {
            execcute = execcuteValue;
            canExecute = canExecuteValue;
        }
        public event EventHandler? CanExecuteChanged
        {
            add
            {
                CommandManager.RequerySuggested += value;
            }
            remove
            {
                CommandManager.RequerySuggested -= value;
            }
        }

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

        public void Execute(object? parameter)
        {
            execcute(parameter);
        }
    }

    public class Book
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Title { get; set; }
        public string ISBN { get; set; }
        public ImageSource ImgSource { get; set; }
    }
}