You can't directly call event.getSource() because that method doesn't exist on API 8. Instead, you need to use the AccessibilityRecordCompat and AccessibilityNodeInfoCompat classes.
AccessibilityRecordCompat record = AccessibilityEventCompat.asRecord(event);
AccessibilityNodeInfoCompat node = record.getSource();
Log.i(TAG, node.getViewIdResourceName());
These classes wrap the actual event and node objects, and they provide stub implementations when methods are not available on the current device API. So if you run the snippet above on API 8, it will crash with a NullPointerException because getSource() is an API 14+ method and will always return null on earlier APIs.