c++ enable accessibility inspection in Google Chrome

Question

I'm trying to access text of Google Chrome's webpage to read it and offer some actions (for example, remind). Everything works good, but I need to enable accessibility inspection programmatically. I use this code:

wchar_t className[100];
GetClassName(hwnd, className, 100) == 0 || wcscmp(className, L"Chrome_WidgetWin_1");

CComPtr<IAccessible> pAccMain;
HRESULT hr = ::AccessibleObjectFromWindow(hWndChrome, 1, IID_IAccessible, (void**)(&pAccMain));

CComPtr<IAccessible> pAccMain2;
::AccessibleObjectFromWindow(hWndChrome, OBJID_CLIENT, IID_IAccessible, (void**)(&pAccMain2));

And nothing happens until I run browser with --force-renderer-accessibility parameter or manually change accessibility settings located in chrome://accessibility.

What am i doing wrong?

Found this info: "Chrome calls NotifyWinEvent with EVENT_SYSTEM_ALERT and the custom object id of 1. If it subsequently receives a WM_GETOBJECT call for that custom object id, it assumes that assistive technology is running". Does anybody know how to implement this?

Answer 1

Use SetWinEventHook, e.g.

HWINEVENTHOOK hook = SetWinEventHook(EVENT_SYSTEM_ALERT, EVENT_SYSTEM_ALERT,NULL, WinEventProc, 0, 0, WINEVENT_OUTOFCONTEXT)

Then in your WinEventProc, you'll be given a hWnd, idObject, and idChild when Chrome sends the EVENT_SYSTEM_ALERT.

If idObject == 1 then call AccessibleObjectFromEvent(), passing it those hWnd, idObject, and idChild arguments.

AccessibleObjectFromEvent will then send the WM_GETOBJECT. From the docs::

Applications never send this message directly. Microsoft Active Accessibility sends this message in response to calls to AccessibleObjectFromPoint, AccessibleObjectFromEvent, or AccessibleObjectFromWindow.

By using AccEvent I can see that Google Chrome only appears to send the EVENT_SYSTEM_ALERT when it starts, e.g. opening a new tab doesn't trigger it, so you'd need to have done the SetWinEventHook() before Chrome is launched.