At Run Time ButtonAdd_Click is not working. doesn't go to hanndle that events at frmDietChart.aspx.cs

a) frmDietChart.aspx
  <asp:TemplateField HeaderText="Meal Type">
                                <ItemTemplate>
                                    <asp:DropDownList ID="ddlMealType" DataTextField="Name" DataValueField="Id" DataSource='<%#objBLLCombo.FillMealType()%>'
                                        runat="server" Width="90px" />
                                </ItemTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="Item Name">
                                <ItemTemplate>
                                    <asp:DropDownList ID="ddlItemName" DataTextField="Name" DataValueField="Id" DataSource='<%#objBLLCombo.FillMealItem()%>'
                                        runat="server" Width="90px" />
                                </ItemTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="Unit">
                                <ItemTemplate>
                                    <asp:DropDownList ID="ddlUnit" DataTextField="Name" DataValueField="Id" DataSource='<%#objBLLCombo.FillMealItemUnit()%>' runat="server" Width="120px" />
                                </ItemTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="Quantity">
                                <ItemTemplate>
                                    <asp:TextBox ID="txtQuantity" runat="server" Width="70px" />
                                </ItemTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="Calories">
                                <ItemTemplate>
                                    <asp:TextBox ID="txtCalories" runat="server" Width="70px" />
                                </ItemTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="Total Calories">
                                <ItemTemplate>
                                    <asp:TextBox ID="txtTotCalories" runat="server" Width="70px" />
                                </ItemTemplate>
                                <FooterStyle HorizontalAlign="Right" />
                                <FooterTemplate>
                                    <asp:Button ID="ButtonAdd" runat="server" Text="Add New Row" OnClick="ButtonAdd_Click" />
                                </FooterTemplate>
                            </asp:TemplateField>
b) frmDietChart.aspx.cs
  protected void ButtonAdd_Click(object sender, EventArgs e)
    {
        AddRowToGrid();
    }
    private void AddRowToGrid()
    {
        int id = Convert.ToInt32(ViewState["ID"]);
        if (ViewState["DietChartDetailTable"] != null)
        {
            DataTable dt = (DataTable)ViewState["DietChartDetailTable"];
            DataRow dr = dt.NewRow();
        dr["Id"] = id + 1;
        dr["DietChartId"] = 0;
        dr["DietChartDetailId"] = 0;
        dr["MealTypeId"] = 0;
        dr["MealTypeName"] = string.Empty;
        dr["MealItemId"] = 0;
        dr["MealItemName"] = string.Empty;
        dr["MealItemUnitId"] = 0;
        dr["MealItemUnitName"] = string.Empty;
        dr["Quantity"] = 0;
        dr["Calories"] = 0;
        dr["TotalCalories"] = 0;
        dt.Rows.Add(dr);
        ViewState["DietChartDetailTable"] = dt;
        ViewState["ID"] = id;
        gvDietChartDetail.DataSource = dt;
        gvDietChartDetail.DataBind();
        }
        else
        {
            Response.Write("ViewState is null");
        }
    }