UI Automation exposes every piece of the UI to client applications as an AutomationElement. Elements are contained in a tree structure, with the desktop as the root element. Clients can filter the raw view of the tree as a control view or a content view. (These standard views of the structure can easily be seen by using the UI Spy application included with this software development kit (SDK)). Applications can also create custom views.
AutomationElement objects expose common properties of the UI elements they represent. One of these properties is the control type, which defines its basic appearance and functionality as a single recognizable entity: for example, a button or check box.
In addition, elements expose control patterns that provide properties specific to their control types. Control patterns also expose methods that enable clients to get further information about the element and to provide input.
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There is not a one-to-one correspondence between control types and control patterns. A control pattern may be supported by multiple control types, and a control may support multiple control patterns, each of which exposes different aspects of its behavior. For example, a combo box has at least two control patterns: one that represents its ability to expand and collapse, and another that represents the selection mechanism. For specifics, see
UI Automation Control Types.
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UI Automation also provides information to client applications through events. Unlike WinEvents, UI Automation events are not based on a broadcast mechanism. UI Automation clients register for specific event notifications and can request that specific UI Automation properties and control pattern information be passed into their event handlers. In addition, a UI Automation event contains a reference to the element that raised it. Providers can improve performance by raising events selectively, depending on whether any clients are listening.