I'm facing a bizarre issue with the Apple's Accessibility APIs. I am registering an AXObserver that listens for, among other things, the kAXSelectedTextChangedNotification. For many new users, the kAXSelectTextChangedNotification is not triggered, even though they have enabled Accessibility permission for the app. Other notifications are getting through (kAXWindowMovedNotification, kAXWindowResizedNotification, kAXValueChangedNotification etc - full list here), just not the kAXSelectedTextChangedNotification!
We've found that we can reproduce the error by removing accessibility permission for the app and rebooting our computers. After restarting and reenabling accessibility permissions, the kAXSelectedTextChangedNotification was not received, even though other notifications were fine.
Strangely, the issue can be resolved by launching Apple's Accessibility Inspector app on an impacted computer. Once the Accessibility Inspector is loaded, the kAXSelectedTextChangedNotifications start coming through as expected. This implies to me that either:
We are missing some needed setup when starting the observers. Accessibility Inspector gets it right, thus ‘starting’ the system properly.
Accessibility Inspector is using some Apple private APIs that we don’t have access to.
Things I’ve tried:
I've tried subscribing the AXSelectedTextChangedNotification to different AXUIElements, including the SystemWide element, the Application element, and children elements from the AXApplication. None of these received the kAXSelectedTextChangedNotification, until Accessibility Inspector is booted up. No surprises here, as Apple's documentation confirms that you should add the notification to the root Application AXUIElement if you want to receive notifications for all its children.
I had a theory that the issue might be due to my code calling AXUIElementCreateApplication multiple times, possibly creating multiple "Applications" in Apple's Accessibility implementation. If that’s the case, the notifications might be sent to the wrong application AXUIElement. However, refactoring my code to only call AXUIElementCreateApplication once didn't resolve the issue.
I thought the issue may be caused by subscribing the AXSelectedTextChangedNotification on the high-level application element (at odds with Apple's documentation). I've tried traversing the child AXUIElements until we find one with the kAXSelectedTextAttribute and then subscribing to that. This did not resolve the issue. I don’t think it's the correct path to continue exploring, given that the notifications are received correctly after AccessibilityInspector is launched.
There is one exception to the above: if I add the kSelectedTextChangedNotification listener to a specific text field AXUIElement, I do receive the notification on that text field. However, this is not practical; I need a solution that will work for all text fields within an app. The Accessibility Inspector appears to be doing something that causes the selected-text-changed notifications to be correctly passed up to the high-level application AXUIElement.
Another thought is that I could traverse the entire Accessibility hierarchy and add listeners to every subview that has the kAXSelectedTextAttribute. However, I don’t like this long-term solution. It will be slow and incomplete: new elements get added and removed frequently. I just want the kAXSelectedTextChangedNotification to be received by the high-level Application AXUIElement, which the documentation suggests it should be. I also have evidence that this can work, since notifications start coming through after Accessibility Inspector is launched. It’s just a matter of discovering how to replicate whatever Accessibility Inspector is doing.
An interesting wrinkle: I implemented the 'traverse' strategy above, but was surprised by how few elements were in the hierarchy. Most apps only go down ~2-3 levels, which didn't seem right to me. Perhaps the Accessibility tree isn't fully initialized? I tried adding a 5-second delay to allow more initialization time, but it didn't change anything.
Does anyone have any ideas? Here's our file.
