wpf-rule-virtualization-patterns

Virtualization Patterns

UI virtualization rules for WPF controls that display large collections.

---

ItemsControl with VirtualizingStackPanel

Plain ItemsControl does not virtualize by default — it materializes every item at load. For large collections, replace the default panel with VirtualizingStackPanel and enable container recycling.

<!-- Wrong: no virtualization, all items materialized at once -->
<ItemsControl ItemsSource="{Binding LargeCollection}">
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <StackPanel />
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>
</ItemsControl>

<!-- Correct: VirtualizingStackPanel with recycling -->
<ItemsControl ItemsSource="{Binding LargeCollection}"
              VirtualizingPanel.IsVirtualizing="True"
              VirtualizingPanel.VirtualizationMode="Recycling"
              VirtualizingPanel.ScrollUnit="Pixel"
              ScrollViewer.CanContentScroll="True">
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <VirtualizingStackPanel />
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>
</ItemsControl>

---

ListView / ListBox Attached Properties

ListView and ListBox use a VirtualizingStackPanel by default, but the optimal settings must still be set explicitly via attached properties:

<ListView ItemsSource="{Binding LargeCollection}"
          VirtualizingPanel.IsVirtualizing="True"
          VirtualizingPanel.VirtualizationMode="Recycling"
          VirtualizingPanel.ScrollUnit="Pixel"
          ScrollViewer.CanContentScroll="True">
    ...
</ListView>

---

Key Settings

Attached Property	Recommended Value	Effect
VirtualizingPanel.IsVirtualizing	True	Enable UI virtualization
VirtualizingPanel.VirtualizationMode	Recycling	Reuse containers instead of re-creating
VirtualizingPanel.ScrollUnit	Pixel	Smooth pixel scrolling (vs. item-by-item)
ScrollViewer.CanContentScroll	True	Required for panel-level virtualization