The zero-based column's index among the sorted columns.
Use the SortBy method to sort data in the grid.
Single-Column Sorting (Default) The grid allows data sorting by a single column only, if the DataGridView.SortMode property is set to Single. In this case, when you call the SortBy method, the grid discards the previously applied sorting by another column.
Multi-Column Sorting The grid supports multi-column sorting, if the DataGridView.SortMode property is set to Multiple. When you call the SortBy method, the grid does not clear previously applied sorting and uses the new sort order as an additional condition to sort data. The sortIndex parameter specifies the sequence of column sorting.
Another way to sort data in the grid by column values is to use the column's GridColumn.SortOrder property. To specify the sorting sequence applied to multiple columns, use the GridColumn.SortIndex of these columns.
To specify whether the grid should sort data by cell values or display text, use the GridColumn.SortMode property.