Gridview Sorting by Programming

Protected Sub GridView1_Sorting(sender As Object, e As System.Web.UI.WebControls.GridViewSortEventArgs) Handles GridView1.Sorting
ds.Tables("dt").DefaultView.Sort = e.SortExpression '& " " & GetSortDirection(e.SortExpression)
GridView1.DataSource = ds.Tables("dt")
GridView1.DataBind()
End Sub

Private Function GetSortDirection(ByVal column As String) As String
' By default, set the sort direction to ascending.
Dim sortDirection = "ASC"
' Retrieve the last column that was sorted.
Dim sortExpression = TryCast(ViewState("SortExpression"), String)

If sortExpression IsNot Nothing Then
' Check if the same column is being sorted.
' Otherwise, the default value can be returned.
If sortExpression = column Then
Dim lastDirection = TryCast(ViewState("SortDirection"), String)
If lastDirection IsNot Nothing _
AndAlso lastDirection = "ASC" Then
sortDirection = "DESC"
End If
End If
End If

' Save new values in ViewState.
ViewState("SortDirection") = sortDirection
ViewState("SortExpression") = column

Return sortDirection
End Function