WindowFromAccessibleObject() fails for VirtualBox IAccessible objects

[James Teh]

WindowFromAccessibleObject() is used to retrieve the window handle (hwnd) of an IAccessible (MSAA) object. When calling WindowFromAccessibleObject() on any IAccessible object exposed by VirtualBox, an RPC_E_CANTCALLOUT_ININPUTSYNCCALL error is returned. The text of this error is: "An outgoing call cannot be made since the application is dispatching an input-synchronous call."

WindowFromAccessibleObject() uses the GetWindow() method of the IOleWindow interface. I suspect it is this that is failing. Note that this works fine in other QT4 applications such as Nokia PC Suite and ​Rockbox Utility, so this appears to be a peculiarity of VirtualBox.

​NVDA needs to retrieve the window handle for any IAccessible object, as there is no unique identifier for IAccessible and we need some way of reasonably checking for equality between two objects.

[James Teh]

Ack. The ! shouldn't be at the start of the summary - I forgot Trac doesn't do wiki formatting for ticket summaries. :(

[James Teh]

This issue causes NVDA's navigation to related objects (parents, children and sibblings) to fail. This results in many problems with VirtualBox and NVDA, such as ignored focus events for list/tree controls (see comment:ticket:3590:1), inability to read captions in dialogs and broken object navigation commands. We could try to make NVDA more tolerant when a window handle cannot be retrieved, but this causes comparison problems and means that information such as process ID and window class name cannot be retrieved, which is why we do not currently allow this.

[James Teh]

This now seems to work for *some* accessible objects, but still not all. It works for lists, trees, toolbars, etc. However, it still fails for the outer UI (the application object, panes, etc.)

[aeichner]

Please reopen if still relevant with a recent VirtualBox release.