code: public boolean isSelected(int dataIndex) {
          return mItemAdapter != null &&
                  dataIndex < mItemAdapter.getCount() &&
                  mSelectedItemsList.contains(dataIndex);
      }
docs: Check whether the item at position {@code pos} is selected.
  
  @param dataIndex
  item position in adapter
  @return {@code true} if the item is selected, {@code false} otherwise.