docs: public final void setGravity(@GravityAttr int selectionGravity) {
          mOrientationState.setSelectionGravity(selectionGravity);
          //note that mFlContainerSelected should be in FrameLayout
          FrameLayout.LayoutParams params = (LayoutParams) mFlContainerSelected.getLayoutParams();
          params.gravity = mOrientationState.getSelectionGravity();
          mOrientationState.setSelectionMargin(mSelectionMargin, params);
          mFlContainerSelected.setLayoutParams(params);
          mSelectionGravity = selectionGravity;
          invalidate();
          if (mOuterAdapter != null) {
              mOuterAdapter.setSelectedGravity(selectionGravity);
          }
      }