IUIAutomation::AddFocusChangedEventHandler method (uiautomationclient.h)

Article
10/13/2021

Registers a method that handles focus-changed events.

Note Before implementing an event handler, you should be familiar with the threading issues described in Understanding Threading Issues.

Syntax

HRESULT AddFocusChangedEventHandler(
  [in] IUIAutomationCacheRequest             *cacheRequest,
  [in] IUIAutomationFocusChangedEventHandler *handler
);

Parameters

[in] cacheRequest

Type: IUIAutomationCacheRequest*

A pointer to a cache request, or NULL if no caching is wanted.

[in] handler

Type: IUIAutomationFocusChangedEventHandler*

A pointer to the object that handles the event.

Return value

Type: HRESULT

If this method succeeds, it returns S_OK. Otherwise, it returns an HRESULT error code.

Remarks

Focus-changed events are system-wide; you cannot set a narrower scope.

A UI Automation client should not use multiple threads to add or remove event handlers. Unexpected behavior can result if one event handler is being added or removed while another is being added or removed in the same client process.

Examples

The following example function creates an object that implements IUIAutomationFocusChangedEventHandler and subscribes to the event by adding the handler.

HRESULT AddFocusHandler(IUIAutomation* pAutomation)
{ 
    // CFocusHandler is a class that implements IUIAutomationFocusChangedEventHandler. 
    CFocusHandler* pFocusHandler = new CFocusHandler();
    if (!pFocusHandler)
    {
        return E_OUTOFMEMORY;
    }
    IUIAutomationFocusChangedEventHandler* pHandler;
    pFocusHandler->QueryInterface(IID_IUIAutomationFocusChangedEventHandler, (void**)&pHandler);
    HRESULT hr = pAutomation->AddFocusChangedEventHandler(NULL, pHandler);
    pFocusHandler->Release();
    return hr;
}

Requirements

Requirement	Value
Minimum supported client	Windows 7, Windows Vista with SP2 and Platform Update for Windows Vista, Windows XP with SP3 and Platform Update for Windows Vista [desktop apps only]
Minimum supported server	Windows Server 2008 R2, Windows Server 2008 with SP2 and Platform Update for Windows Server 2008, Windows Server 2003 with SP2 and Platform Update for Windows Server 2008 [desktop apps only]
Target Platform	Windows
Header	uiautomationclient.h (include UIAutomation.h)