VirtualizedItem Control Pattern
Describes guidelines and conventions for implementing IVirtualizedItemProvider, including information about properties and methods. The VirtualizedItem control pattern is used to support virtualized items, which are items that are represented by placeholder automation elements in the Microsoft UI Automation tree.
Virtualized items can include items retrieved from a control that supports the ItemContainer control pattern, or a virtualized embedded object retrieved from a control that supports the Text control pattern. The placeholder for a virtualized item might not have loaded data for all UI Automation properties, and may return UIA_E_ELEMENTNOTAVAILABLE in response to queries for properties that are not available. The VirtualizedItem control pattern provides a method for realizing a virtual item so that full information is made available for the item, and a full automation element can be created for the item in the UI Automation tree.
This topic contains the following sections.
- Implementation Guidelines and Conventions
- Required Members for IVirtualizedItemProvider
- Related topics
When implementing the VirtualizedItem control pattern, note the following guidelines and conventions:
- Any UI Automation placeholder element that can be virtualized must support the VirtualizedItem control pattern by exposing the IVirtualizedItemProvider interface.
- When IVirtualizedItemProvider::Realize is called, the placeholder object must be updated with full implementations of its properties and control patterns.
- When IVirtualizedItemProvider::Realize is called, the provider can change the viewport so that the virtualized item comes into view. Bringing the item into view is not required; however, off-screen, non-virtualized items should support the IScrollItemProvider::ScrollIntoView method.
The following properties and methods are required for implementing the IVirtualizedItemProvider interface.
|Required members||Member type||Notes|
This control pattern has no associated events.
- Implementing the UI Automation ItemContainer Control Pattern
- UI Automation Control Patterns Overview
- UI Automation Tree Overview
- Working with Virtualized Items