Loading indicator until DeviceActivityReport renders?

There is frequently a delay of a few seconds before a DeviceActivityReport renders its view generated from the DeviceActivityReportExtension. It will also sometimes flash with zero data before hydrating with the real activity data (tested with extension code taken directly from XCode boilerplate)

Is there a way to be notified when the DeviceActivityReport renders successfully or is still processing, i.e. so a loading indicator can be presented while the extension runs?

Thanks!