How to sort a manual GridView?

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
 
        Dim pdb As cPlansDatabase = Session("Database")
        Me.Label3.Text = Trim(Str(pdb.PlansTable.RowCount))
        GridView9.AllowSorting = True
        FillGridTable(pdb.PlansTable, GridView9, New String() {"Plan Number", "Project Number"}, New String() {"Plan #", "Project #"})
 
    End Sub
 
 
 
    Private Sub FillGridTable(ByVal mt As cMyDataTable, ByVal gv As GridView, ByVal fields() As String, Optional ByVal colnames() As String = Nothing)
 
        Dim dt As New Data.DataTable
 
        If Not colnames Is Nothing Then
            For Each s As String In colnames
                dt.Columns.Add(s)
            Next
        Else
            For Each s As String In fields
                dt.Columns.Add(s)
            Next
        End If
 
        Dim dr As Data.DataRow
 
        Dim o(fields.Length - 1) As Object
        Dim i As Integer
 
        For n As Integer = 0 To mt.RowCount - 1
            dr = mt.Table.Rows(n)
 
            i = 0
 
            For m As Integer = 0 To fields.Length - 1
                o(i) = dr.Item(fields(m))
                i += 1
            Next
 
            dt.Rows.Add(o)
        Next
 
        gv.DataSource = dt
        gv.DataBind()
 
    End Sub