After you've set the SortParameterName on the ObjectDataSource and enabled sorting on the GridView, when the user clicks on a column header the value of the column's SortExpression will be passed to ...

The GridView has two columns: the first column displays the string and the second has a Button that should perform an action based on the string value.

Once you do that, you'll find that the SmartTag for the GridView has an Enable Sorting option that you can check off. However, turning on the sort option just enables the user interface support (the ...