Adding gridveiw row values

[Garudzo]

I am developing an application using the gridview. the last column is a total column I want to compare the typed in value to the sum of values in the rest of the cells. I tried to use custom validation but the textboxes that contain the values are not seen by the application below is my validation code

    Protected Sub validateTotals(ByVal source As Object, _
    ByVal args As System.Web.UI.WebControls.ServerValidateEventArgs) _
  
        Dim total, sums As Integer
        Dim txtBox As TextBox

        sums = 0
        txtBox = CType(GridView1.FindControl("Textbox1"), TextBox)
        total = CInt(txtBox.Text)
        txtBox = CType(GridView1.FindControl("Textbox1"), TextBox)
        sums += CInt(txtBox.Text)
        txtBox = CType(GridView1.FindControl("Textbox2"), TextBox)
        sums += CInt(txtBox.Text)
        txtBox = CType(GridView1.FindControl("Textbox3"), TextBox)
        sums += CInt(txtBox.Text)
        txtBox = CType(GridView1.FindControl("Textbox4"), TextBox)
        sums += CInt(txtBox.Text)
        txtBox = CType(GridView1.FindControl("Textbox5"), TextBox)
        sums += CInt(txtBox.Text)
        txtBox = CType(GridView1.FindControl("Textbox6"), TextBox)
        sums += CInt(txtBox.Text)
        If sums <> total Then
            args.IsValid = False
        Else
            args.IsValid = True
        End If

    End Sub

I have also tried JavaScript which works fine if the user navigates through all the other cells but if not it does not work

Please help