WPF UI Virtualization

Quick Setup

<ListBox ItemsSource="{Binding LargeCollection}" VirtualizingPanel.IsVirtualizing="True" VirtualizingPanel.VirtualizationMode="Recycling" VirtualizingPanel.ScrollUnit="Pixel" VirtualizingPanel.CacheLength="2,2" VirtualizingPanel.CacheLengthUnit="Page"/>

Key Properties

Property Recommended Purpose

IsVirtualizing

True Enable virtualization

VirtualizationMode

Recycling Reuse containers

ScrollUnit

Pixel Smooth scrolling

CacheLength

"1,1" to "2,2" Buffer pages

Virtualization Breakers

These disable virtualization:

<!-- ❌ ScrollViewer wrapper --> <ScrollViewer> <ListBox/> </ScrollViewer>

<!-- ❌ CanContentScroll disabled --> <ListBox ScrollViewer.CanContentScroll="False"/>

<!-- ❌ Grouping without flag --> <ListBox> <ListBox.GroupStyle>...</ListBox.GroupStyle> </ListBox>

Fixes:

<!-- ✅ No wrapper needed - ListBox has built-in ScrollViewer --> <ListBox ItemsSource="{Binding Items}"/>

<!-- ✅ Grouping with virtualization --> <ListBox VirtualizingPanel.IsVirtualizingWhenGrouping="True"> <ListBox.GroupStyle>...</ListBox.GroupStyle> </ListBox>

Recycling Mode Considerations

// When using Recycling mode, clean up in PrepareContainerForItemOverride protected override void PrepareContainerForItemOverride( DependencyObject element, object item) { base.PrepareContainerForItemOverride(element, item);

var container = (ListBoxItem)element;
// Reset any manually attached handlers or state

}

Performance Tips

Deferred Scrolling

<!-- Faster scrollbar dragging --> <ListBox ScrollViewer.IsDeferredScrollingEnabled="True"/>

Diagnostic Check

public static bool IsVirtualizing(ItemsControl control) { var panel = FindVisualChild<VirtualizingStackPanel>(control); return panel != null && VirtualizingPanel.GetIsVirtualizing(control); }

public static int GetRealizedCount(ItemsControl control) { var generator = control.ItemContainerGenerator; return Enumerable.Range(0, control.Items.Count) .Count(i => generator.ContainerFromIndex(i) != null); }

DataGrid Virtualization

<DataGrid ItemsSource="{Binding Items}" EnableRowVirtualization="True" EnableColumnVirtualization="True" VirtualizingPanel.IsVirtualizing="True" VirtualizingPanel.VirtualizationMode="Recycling"/>