title: update panel - dropdown selected index change event not triggering
body: <p>I have one dropdownlist on my page (.aspx) and based on change of selected value i need to bind the data to checkboxlist control which is on the same page. To avoid entire page to be refreshed, i have put the controls in the update panel.</p>
  
  <p>But when i am changes the selection from the dropdown,, it is getting back to the first value itself and the selected index changed even is not getting triggered.
    here is how I have put my controls in the update panel.</p>
  
  <pre><code>&lt;asp:Content ID="Main" ContentPlaceHolderID="PlaceHolderMain" runat="server"&gt;
      &lt;asp:ScriptManagerProxy ID="ScriptManagerProxy1" runat="server"&gt;&lt;/asp:ScriptManagerProxy&gt;
      &lt;asp:UpdatePanel ID="UpdatePanel1" runat="server"&gt;
     &lt;ContentTemplate&gt;
         &lt;fieldset&gt;
             &lt;div id="attachmentdiv"&gt;
                 &lt;asp:DropDownList ID="ddlimportfiles" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddlimportfiles_onselectedindexChange"&gt;&lt;/asp:DropDownList&gt;
             &lt;/div&gt;
             &lt;div id="voltagediv"&gt;
                 &lt;asp:CheckBoxList ID="chkBoxLstVoltage" runat="server"&gt;&lt;/asp:CheckBoxList&gt;
             &lt;/div&gt;
             &lt;asp:Button ID="btnGenerateZBF" runat="server" Text="Generate ZBF" OnClick="GenerateZBF_Click" /&gt;
         &lt;/fieldset&gt;
     &lt;/ContentTemplate&gt;
          &lt;Triggers&gt;
              &lt;asp:AsyncPostBackTrigger ControlID="ddlimportfiles" EventName="SelectedIndexChanged" /&gt;
          &lt;/Triggers&gt;
  &lt;/asp:UpdatePanel&gt;
  
   &lt;/asp:Content&gt;
  </code></pre>
  
  <p>kindly suggest what I am doing wrong here.</p>