ASP.NET

<asp:Panel ID="Addpn" runat="server" CssClass="Panels">

             <div id="divGrid">

             <asp:GridView ID="gdvItems" runat="server" Visible="true" ShowFooter="true" AutoGenerateColumns="false">
             <Columns >
             <asp:BoundField DataField="ItemNo" HeaderText="ItemNo" />
            <asp:TemplateField HeaderText="TireSize">
            <ItemTemplate>
                <asp:TextBox ID="txtTireSize" runat="server"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="DOT">
            <ItemTemplate>
                <asp:TextBox ID="txtDOT" runat="server"></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>

              <asp:TemplateField HeaderText="RemovalArea">
            <ItemTemplate>
               <asp:TextBox ID="txtReAre" runat="server"></asp:TextBox>
                <%--<asp:DropDownList ID="ddlRemovalArea" runat="server">
                <asp:ListItem>-Select-</asp:ListItem>
                 <asp:ListItem>Bead</asp:ListItem>
                 <asp:ListItem>Tread</asp:ListItem>
                 <asp:ListItem>Sidewalk</asp:ListItem>
                 <asp:ListItem>Other</asp:ListItem>
                 <asp:ListItem>Tread life</asp:ListItem>
                 <asp:ListItem>Interior</asp:ListItem>
                </asp:DropDownList>--%>
            </ItemTemplate>
        </asp:TemplateField>
                <asp:TemplateField HeaderText="TirePosition">
            <ItemTemplate>
             <asp:TextBox ID="txtTireposition" runat="server"></asp:TextBox>
                <%-- <asp:DropDownList ID="ddlTirePosition" runat="server">
                  <asp:ListItem>-Select-</asp:ListItem>
                 <asp:ListItem>Left Front</asp:ListItem>
                  <asp:ListItem>Right Front</asp:ListItem>
                   <asp:ListItem>Left Rear</asp:ListItem>
                    <asp:ListItem>Right Rear</asp:ListItem>
                     <asp:ListItem>Other</asp:ListItem>
                      <asp:ListItem>Trailer</asp:ListItem>
                 </asp:DropDownList>--%>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText ="Product Code">
        <ItemTemplate>
        <asp:TextBox ID="txtProductCode" runat="server"></asp:TextBox>
        </ItemTemplate>
         </asp:TemplateField>
                <asp:TemplateField HeaderText="ApprovalNumber">
            <ItemTemplate>
                 <asp:TextBox ID="txtApprovalNumber" runat="server"></asp:TextBox>
            </ItemTemplate>
             <FooterStyle HorizontalAlign="Right" />

            <FooterTemplate>

             <asp:Button ID="ButtonAdd" runat="server" Text="Add New Row"  />

            </FooterTemplate>

        </asp:TemplateField>

             </Columns>

             </asp:GridView>

             </div>
             </asp:Panel>

Protected Sub Page_Load(sender As Object, e As EventArgs)


    ' Addpn.Visible = True
    ' SetInitialRow()
    If Not Page.IsPostBack Then
        SetInitialRow()
    End If

End Sub

Private Sub SetInitialRow()
    Try


        Dim dt As DataTable = New DataTable()
        Dim dr As DataRow = Nothing
        dt.Columns.Add(New DataColumn("ItemNo", GetType(String)))
        dt.Columns.Add(New DataColumn("TireSize", GetType(String)))
        dt.Columns.Add(New DataColumn("DOT", GetType(String)))
        dt.Columns.Add(New DataColumn("RemovalArea", GetType(String)))
        dt.Columns.Add(New DataColumn("TirePosition", GetType(String)))
        dt.Columns.Add(New DataColumn("ApprovalNumber", GetType(String)))
        dr = dt.NewRow()
        dr("ItemNo") = 1
        dr("TireSize") = String.Empty
        dr("DOT") = String.Empty
        dr("RemovalArea") = String.Empty
        dr("TirePosition") = String.Empty
        dr("ApprovalNumber") = String.Empty
        dt.Rows.Add(dr)
        ViewState("EmptyData") = dt
        Dim ds As DataSet = New DataSet()
        ds.Tables.Add(dt)
        If (dt.Rows.Count > 0) Then
            gdvItems.DataSource = ds
            gdvItems.DataBind()
        Else
            gdvItems.DataSource = Nothing
            gdvItems.DataBind()
        End If


    Catch ex As Exception
        '  Return IsError()
    End Try


End Sub
Private Sub AddNewRowToGrid()
    Dim rowIndex As Integer = 0

    If ViewState("CurrentTable") IsNot Nothing Then
        Dim dtCurrentTable As DataTable = DirectCast(ViewState("CurrentTable"), DataTable)
        Dim drCurrentRow As DataRow = Nothing
        If dtCurrentTable.Rows.Count > 0 Then
            For i As Integer = 1 To dtCurrentTable.Rows.Count
                'extract the TextBox values
                Dim box1 As TextBox = DirectCast(gdvItems.Rows(rowIndex).Cells(1).FindControl("txtTireSize"), TextBox)
                Dim box2 As TextBox = DirectCast(gdvItems.Rows(rowIndex).Cells(2).FindControl("txtDOT"), TextBox)
                Dim box3 As TextBox = DirectCast(gdvItems.Rows(rowIndex).Cells(3).FindControl("txtReAre"), TextBox)

                drCurrentRow = dtCurrentTable.NewRow()
                drCurrentRow("RowNumber") = i + 1

                dtCurrentTable.Rows(i - 1)("Column1") = box1.Text
                dtCurrentTable.Rows(i - 1)("Column2") = box2.Text
                dtCurrentTable.Rows(i - 1)("Column3") = box3.Text

                rowIndex += 1
            Next
            dtCurrentTable.Rows.Add(drCurrentRow)
            ViewState("CurrentTable") = dtCurrentTable

            gdvItems.DataSource = dtCurrentTable
            gdvItems.DataBind()
        End If
    Else
        Response.Write("ViewState is null")
    End If

    'Set Previous Data on Postbacks
    SetPreviousData()
End Sub
Private Sub SetPreviousData()
    Dim rowIndex As Integer = 0
    If ViewState("CurrentTable") IsNot Nothing Then
        Dim dt As DataTable = DirectCast(ViewState("CurrentTable"), DataTable)
        If dt.Rows.Count > 0 Then
            For i As Integer = 0 To dt.Rows.Count - 1
                Dim box1 As TextBox = DirectCast(gdvItems.Rows(rowIndex).Cells(1).FindControl("txtTireSize"), TextBox)
                Dim box2 As TextBox = DirectCast(gdvItems.Rows(rowIndex).Cells(2).FindControl("txtDOT"), TextBox)
                Dim box3 As TextBox = DirectCast(gdvItems.Rows(rowIndex).Cells(3).FindControl("txtReAre"), TextBox)
                Dim box4 As DropDownList = DirectCast(gdvItems.Rows(rowIndex).Cells(4).FindControl("ddlTireposition"), DropDownList)

                box1.Text = dt.Rows(i)("Column1").ToString()
                box2.Text = dt.Rows(i)("Column2").ToString()
                box3.Text = dt.Rows(i)("Column3").ToString()
                box4.Text = dt.Rows(i)("Column4").ToString()

                rowIndex += 1
            Next
        End If
    End If
End Sub

Protected Sub ButtonAdd_Click(sender As Object, e As EventArgs)
    AddNewRowToGrid()
End Sub