Fire Dropdownlist In Gridview Row When Edit Button Is Clicked

Hi,

I have a dropdownlist in gridview edit row. The dropdownlist only works when i select any item which ofcourse is the normal behaviour but my requirement is for it to fire with the current value and behaviour once i click edit button.

it should act as if it's a new selection but it should retain current value.

I don't know if i should call it reload or refresh

Below is the dropdown code:

Protected Sub TaxnameDrp_SelectedIndexChanged(sender As Object, e As EventArgs)
        Dim strConnString As String = ConfigurationManager.ConnectionStrings("ConnString").ConnectionString()
        Dim TaxnameDrp As DropDownList = DirectCast(sender, DropDownList)
        Dim TaxName As String = TaxnameDrp.SelectedValue

        ' Get the GridViewRow in which this master DropDownList exists
        Dim row As GridViewRow = DirectCast(TaxnameDrp.NamingContainer, GridViewRow)
        Dim txt As TextBox = DirectCast(row.FindControl("txtTaxamt2"), TextBox)
        Dim stotal As TextBox = DirectCast(row.FindControl("txtSubtotal2"), TextBox)
        Dim strQuery As String = "select TaxID, TaxName, [Rate(%)] from Tax where" & " TaxID = @TaxID"

        Dim con As New SqlConnection(strConnString)

        Dim cmd As New SqlCommand()
        cmd.Parameters.AddWithValue("@TaxID", TaxnameDrp.SelectedItem.Value)

        
        cmd.CommandType = CommandType.Text

        cmd.CommandText = strQuery

        cmd.Connection = con

        Try

            con.Open()

            Dim sdr As SqlDataReader = cmd.ExecuteReader()

            While sdr.Read()


                txt.Text = Convert.ToDecimal(Math.Round(sdr(2).ToString() * stotal.Text.Trim()) / 100).ToString("N2", CultureInfo.CreateSpecificCulture("en-US"))

                hdfTaxName.Value = sdr(2).ToString()

            End While

        Catch ex As Exception

            Throw ex

        Finally


            con.Close()
            con.Dispose()

        End Try

    End Sub

Thanks in advance