code: private void updateCursorObserver() {
          Cursor newObservedCursor = getDataObserverCount() > 0 ? mCursor : null;
          if (newObservedCursor != mObservedCursor) {
              if (mObservedCursor != null) {
                  mObservedCursor.unregisterContentObserver(mCursorContentObserver);
              }
              mObservedCursor = newObservedCursor;
              if (mObservedCursor != null) {
                  mObservedCursor.registerContentObserver(mCursorContentObserver);
              }
          }
      }
docs: Registers or unregisters with the cursor. Idempotent.