UIA: handle structure change events

[josephsl]

Hi,

Structure change events are used to let clients know if something was added or removed in a container (as far as I can tell). At the moment NVDA's UIA handler does not recognize this event. However, there are scenarios that uses this event, with one of them being Skype Preview UWP (Universal Windows Platform) app where structure change event is fired whenever a new message is received (Skype Preview app support is another ticket of its own). Thus I'd like to propose adding support for at least structure change/add event in NVDA. Thanks.

[derekriemer]

Could this be request only since watching these too boldly might result
in floods?

On 8/5/2016 2:25 AM, Joseph Lee wrote:

Hi,

Structure change events are used to let clients know if something was
added or removed in a container (as far as I can tell). At the moment
NVDA's UIA handler does not recognize this event. However, there are
scenarios that uses this event, with one of them being Skype Preview
UWP (Universal Windows Platform) app where structure change event is
fired whenever a new message is received (Skype Preview app support is
another ticket of its own). Thus I'd like to propose adding support
for at least structure change/add event in NVDA. Thanks.

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[jcsteh]

I tend to agree that this would need to be request only. The question is how we'd do this. It can't be done simply with eventHandler.requestEvents, since that function intentionally doesn't know about API specific stuff but UIA requires a root element to listen beneath. Perhaps we'd need to add a function in UIAHandler for this.

[josephsl]

Hi,

Recent WinTenApps add-on work on letting NVDA listen to additional events without resorting to restarting UIA handler yielded some possibilities:

1. The nondestructive way to add additional event listeners is to add the needed event and corresponding NVDA event to event maps in UIA handler.
2. Call UIAHandler.handler.clientObject.add* functions (there are three defined so far, representing focus changes, property changes and generic events).
3. There is indeed a function to allow clients to listen to structure change event.

Although this ticket will focus on structure change event, I propose a more generic solution (another ticket) so app modules, global plugins, NVDA objects and so on can tell NVDA to subscribe to (and move away from) additional events. In case of structure change, what's needed is defining UIAHandler.handler.clientObject.AddStructureChangedEventHandler that must take UIA info for an element (in order to avoid a storm of these events), and tell NVDA to do something about it somewhere.

Thanks.

[josephsl]

Hi,

Coming back to this...

I'm thinking event groups might be of use. However, given that we have more UIA events now and since the most important use case is no longer important (Skype apps has gone through a complete redesign in version 8), I'm favor of closing this issue.

Thanks.

[Adriani90]

Closing as suggested by Joseph above.