<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" OnRowCommand="GridView1_RowCommand"
    DataSourceID="SqlDataSource1">
    <Columns>
        <asp:ButtonField CommandName="insertNew"
    Text="Button" />
        <asp:TemplateField>
            <ItemTemplate>
                <asp:Button ID="btnAdd" runat="server" CommandName="insertNew"
                CommandArgument="<%# CType(Container,GridViewRow).RowIndex %>"
                Text="Add" />
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField></asp:TemplateField>
    </Columns>
</asp:GridView>

Protected Sub GridView1_RowCommand(ByVal sender As Object, _
   ByVal e As System.Web.UI.WebControls.GridViewCommandEventArgs)
    If (e.CommandName = "insertNew") Then

        Dim index As Integer = Convert.ToInt32(e.CommandArgument)
        MsgBox(index)
    End If
End Sub

<httpRuntime maxRequestLength="32768" />