I have been testing a Microsoft supplied sample of a C++ IUIAutomationEventHandler program.
The link to the source code is https://docs.microsoft.com/en-us/windows/desktop/winauto/uiauto-howto-implement-event-handlers#handling-general-ui-automation-events.
I used Visual Studio 2017 to build a standard console application using the sample code on Windows 10.
After starting the UIA application, I then repeatedly started and stopped the Calculator program. The Windows Task Manager revealed that the UIA application handle count kept
growing each time, the Calculator program was started and stopped.
I feel there is some resource is not being freed. Has anyone run across this issue as well, or knows how to prevent the handle leak from occurring?
Below is a copy of the source code from the link above:
// Defines an event handler for general UI Automation events. It listens for
// tooltip and window creation and destruction events.
#include <windows.h>
#include <stdio.h>
#include <UIAutomation.h>
class EventHandler:
public IUIAutomationEventHandler
{
private:
LONG _refCount;
public:
int _eventCount;
// Constructor.
EventHandler(): _refCount(1), _eventCount(0)
{
}
// IUnknown methods.
ULONG STDMETHODCALLTYPE AddRef()
{
ULONG ret = InterlockedIncrement(&_refCount);
return ret;
}
ULONG STDMETHODCALLTYPE Release()
{
ULONG ret = InterlockedDecrement(&_refCount);
if (ret == 0)
{
delete this;
return 0;
}
return ret;
}
HRESULT STDMETHODCALLTYPE QueryInterface(REFIID riid, void** ppInterface)
{
if (riid == __uuidof(IUnknown))
*ppInterface=static_cast<IUIAutomationEventHandler*>(this);
else if (riid == __uuidof(IUIAutomationEventHandler))
*ppInterface=static_cast<IUIAutomationEventHandler*>(this);
else
{
*ppInterface = NULL;
return E_NOINTERFACE;
}
this->AddRef();
return S_OK;
}
// IUIAutomationEventHandler methods
HRESULT STDMETHODCALLTYPE HandleAutomationEvent(IUIAutomationElement * pSender, EVENTID eventID)
{
_eventCount++;
switch (eventID)
{
case UIA_ToolTipOpenedEventId:
wprintf(L">> Event ToolTipOpened Received! (count: %d)\n", _eventCount);
break;
case UIA_ToolTipClosedEventId:
wprintf(L">> Event ToolTipClosed Received! (count: %d)\n", _eventCount);
break;
case UIA_Window_WindowOpenedEventId:
wprintf(L">> Event WindowOpened Received! (count: %d)\n", _eventCount);
break;
case UIA_Window_WindowClosedEventId:
wprintf(L">> Event WindowClosed Received! (count: %d)\n", _eventCount);
break;
default:
wprintf(L">> Event (%d) Received! (count: %d)\n", eventID, _eventCount);
break;
}
return S_OK;
}
};
int main(int argc, char* argv[])
{
HRESULT hr;
int ret = 0;
IUIAutomationElement* pTargetElement = NULL;
EventHandler* pEHTemp = NULL;
CoInitializeEx(NULL,COINIT_MULTITHREADED);
IUIAutomation* pAutomation = NULL;
hr = CoCreateInstance(__uuidof(CUIAutomation), NULL,CLSCTX_INPROC_SERVER, __uuidof(IUIAutomation), (void**)&pAutomation);
if(FAILED(hr) || pAutomation==NULL)
{
ret = 1;
goto cleanup;
}
// Use root element for listening to window and tooltip creation and destruction.
hr = pAutomation->GetRootElement(&pTargetElement);
if (FAILED(hr) || pTargetElement==NULL)
{
ret = 1;
goto cleanup;
}
pEHTemp = new EventHandler();
if (pEHTemp == NULL)
{
ret = 1;
goto cleanup;
}
wprintf(L"-Adding Event Handlers.\n");
hr = pAutomation->AddAutomationEventHandler(UIA_ToolTipOpenedEventId, pTargetElement, TreeScope_Subtree, NULL, (IUIAutomationEventHandler*) pEHTemp);
if (FAILED(hr))
{
ret = 1;
goto cleanup;
}
hr = pAutomation->AddAutomationEventHandler(UIA_ToolTipClosedEventId, pTargetElement, TreeScope_Subtree, NULL, (IUIAutomationEventHandler*) pEHTemp);
if (FAILED(hr))
{
ret = 1;
goto cleanup;
}
hr = pAutomation->AddAutomationEventHandler(UIA_Window_WindowOpenedEventId, pTargetElement, TreeScope_Subtree, NULL, (IUIAutomationEventHandler*) pEHTemp);
if (FAILED(hr))
{
ret = 1;
goto cleanup;
}
hr = pAutomation->AddAutomationEventHandler(UIA_Window_WindowClosedEventId, pTargetElement, TreeScope_Subtree, NULL, (IUIAutomationEventHandler*) pEHTemp);
if (FAILED(hr))
{
ret = 1;
goto cleanup;
}
wprintf(L"-Press any key to remove event handlers and exit\n");
getchar();
wprintf(L"-Removing Event Handlers.\n");
cleanup:
// Remove event handlers, release resources, and terminate
if (pAutomation != NULL)
{
hr = pAutomation->RemoveAllEventHandlers();
if (FAILED(hr))
ret = 1;
pAutomation->Release();
}
if (pEHTemp != NULL)
pEHTemp->Release();
if (pTargetElement != NULL)
pTargetElement->Release();
CoUninitialize();
return ret;
}