Add Multiple row in grid aspx

>asp:gridview ID="Gridview1" runat="server" ShowFooter="true" AutoGenerateColumns="false" >
>Columns>
>asp:BoundField DataField="RowNumber" HeaderText="Row Number" />
>asp:TemplateField HeaderText="Header 1">
>ItemTemplate>
>asp:TextBox ID="TextBox1" runat="server">
>/ItemTemplate>
>/asp:TemplateField>
>asp:TemplateField HeaderText="Header 2">
>ItemTemplate>
>asp:TextBox ID="TextBox2" runat="server">
>/ItemTemplate>
>/asp:TemplateField>
>asp:TemplateField HeaderText="Header 3">
>ItemTemplate>
>asp:TextBox ID="TextBox3" runat="server">
>/ItemTemplate>
>FooterStyle HorizontalAlign="Right" />
>FooterTemplate>
>asp:Button ID="ButtonAdd" runat="server" Text="Add New Row" OnClick="ButtonAdd_Click"/>
>/FooterTemplate>
>/asp:TemplateField>
>/Columns>
>/asp:gridview>