In update panel, gridview Itemtemplate, event not firing

hi

<asp:UpdatePanel ID="pnlHelloWorld" runat="server"  UpdateMode="Conditional">
     <ContentTemplate>
   <asp:GridView ID="GridView1" runat="server"
                   AllowSorting="True" AutoGenerateColumns="False"  
                   Width="793px" CellPadding="0" AllowPaging="True">
                  <Columns>
                       <asp:TemplateField>
                           <ItemTemplate>      <asp:HyperLink ID="AddtoCart" runat="server" Visible ="true"  CommandArgument='<%# Eval("Id") %>' OnClick="Button1_Click" class="addtocart-img1"></asp:HyperLink>

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The button1_click is not firing.. even I have added..

  <triggers>
 <asp:AsyncPostBackTrigger ControlID="AddtoCart" EventName="OnClick" />
</triggers>

below <contenttemplate> of the updatepanel.. any ideas apprecaited