Tree Views and Navigation
The user interface (UI) elements on the screen can be seen as a tree structure with the desktop as the root, application windows as immediate children, and elements within applications as further descendants.
In Active Accessibility, many automation elements that are irrelevant to end users are exposed in the tree. Client applications have to look at all the elements to determine which are meaningful.
UI Automation client applications see the UI through a filtered view. The view contains only elements of interest: those that give information to the user or enable interaction. Predefined views of only control elements and only content elements are available; in addition, applications can define custom views. UI Automation simplifies the task of describing the UI to the user and helping the user interact with the application.
Navigation between elements, in Active Accessibility, is either spatial (for example, moving to the element that lies to the left on the screen), logical (for example, moving to the next menu item, or the next item in the tab order within a dialog box), or hierarchical (for example, moving the first child in a container, or from the child to its parent). Hierarchical navigation is complicated by the fact that child elements are not always objects that implement IAccessible.
In UI Automation, all UI elements are AutomationElement objects that support the same basic functionality. (From the standpoint of the provider, they are objects that implement an interface inherited from IRawElementProviderSimple.) Navigation is mainly hierarchical: from parents to children, and from one sibling to the next. (Navigation between siblings has a logical element, as it may follow the tab order.) You can navigate from any starting-point, using any filtered view of the tree, by using the TreeWalker class. You can also navigate to particular children or descendants by using FindFirst and FindAll; for example, it is very easy to retrieve all elements within a dialog box that support a specified control pattern.
Navigation in UI Automation is more consistent than in Active Accessibility. Some elements such as drop-down lists and pop-up windows appear twice in the Active Accessibility tree, and navigation from them may have unexpected results. It is actually impossible to properly implement Active Accessibility for a rebar control. UI Automation enables reparenting and repositioning, so that an element can be placed anywhere in the tree despite the hierarchy imposed by ownership of windows.