WPF ScrollViewer.IsDeferredScrollingEnabled is true can enhance the performance hugely when there is huge items and open virtualpanel

When an items control is using a virtualizing panel and it contains a large number of complex items, setting IsDeferredScrollingEnabled to true can result in a significant performance improvement by avoiding the rendering of intermediate states. Applications such as Microsoft Outlook scroll through long lists in this fashion.

 

<Window x:Class="WpfApp387.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:local="clr-namespace:WpfApp387"
        mc:Ignorable="d" WindowState="Maximized"
        Title="MainWindow" Height="450" Width="800">
    <Window.Resources>
        <local:ItemsList x:Key="itemsList"/>
    </Window.Resources>
    <Grid>
        <ListBox ItemsSource="{StaticResource itemsList}"
                 VirtualizingPanel.IsVirtualizing="True"
                 VirtualizingPanel.CacheLength="100"
                 VirtualizingPanel.CacheLengthUnit="Item"
                 VirtualizingPanel.VirtualizationMode="Recycling"
                 ScrollViewer.IsDeferredScrollingEnabled="True">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Grid>
                        <Image Source="{Binding ImgUrl}" Width="200" Height="500" Stretch="Uniform"/>
                        <TextBlock Text="{Binding Name}" 
                                   HorizontalAlignment="Center"
                                   VerticalAlignment="Center"
                                   FontSize="50"
                                   Foreground="Red"/>
                    </Grid>                    
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</Window>


//cs
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;
using System.IO;

namespace WpfApp387
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }

    public class ItemsList : List<Book>
    {
        public ItemsList()
        {
            var imgsList = Directory.GetFiles(@"../../Images");
            if (imgsList != null && imgsList.Any())
            {
                int imgsCount = imgsList.Count();
                for (int i = 0; i < 1000000; i++)
                {
                    this.Add(new Book()
                    {
                        Id = i,
                        Name = $"Name_{i+1}",
                        Title = $"Title_{i}",
                        Topic = $"Topic_{i}",
                        ImgUrl = imgsList[i % imgsCount]
                    });
                }
            }
        }
    }

    public class Book
    {
        public int Id { get; set; }

        public string Name { get; set; }

        public string Title { get; set; }

        public string Topic { get; set; }

        public string ImgUrl { get; set; }
    }

}