This delegate specifies the parameter list that a subroutine must have to handle the DataGrid.SortCommand event. This event specifies additional information about the selected column (DataGridSortCommandEventArgs.SortExpression), which you can use to build a new data source. This event handler should then rebind the data source to the DataGrid control to update the display.
public delegate void DataGridSortCommandEventHandler(object source, DataGridSortCommandEventArgs e);