Virtualization Patterns Skill

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 |

Notes

VirtualizationMode="Recycling" is almost always preferred over Standard — it avoids GC pressure from container creation/destruction during scroll.
ScrollUnit="Pixel" eliminates the "jumping" effect that occurs with item-based scrolling when items have variable height.
Virtualization is disabled if the ScrollViewer wrapping the items panel has CanContentScroll="False" — always verify this setting.
Do not place a VirtualizingStackPanel inside an ScrollViewer with unconstrained height — it will lose virtualization because all items become "visible".

Agent Skills: Virtualization Patterns

Install this agent skill to your local

Skill Files