code: public DragItemRecyclerView addColumn(final DragItemAdapter adapter, final @Nullable View header, @Nullable View columnDragView, boolean hasFixedItemSize) {
          final DragItemRecyclerView recyclerView = insertColumn(adapter, getColumnCount(), header, hasFixedItemSize);
          setupColumnDragListener(columnDragView, recyclerView);
          return recyclerView;
      }
docs: Adds a column at the last index of the board.
  
  @param adapter          Adapter with the items for the column.
  @param header           Header view that will be positioned above the column. Can be null.
  @param columnDragView   View that will act as handle to drag and drop columns. Can be null.
  @param hasFixedItemSize If the items will have a fixed or dynamic size.
  
  @return The created DragItemRecyclerView.