title: SelectedIndexChanged event of dropDownList not firing in Update Panel
body: <p>SelectedIndexChanged event of dropDownList not firing in Update Panel and also set AutoPostBack="true".</p>
  
  <p>Below is my Design Code:</p>
  
  <pre><code>&lt;asp:UpdatePanel ID="UpdatePanel1" runat="server"&gt;
   &lt;ContentTemplate&gt;
  &lt;asp:DropDownList ID="ddl_TypeofCampaign" runat="server"  CssClass="form-control" AutoPostBack="true" OnSelectedIndexChanged="ddl_TypeofCampaign_SelectedIndexChanged" AppendDataBoundItems="true" ViewStateMode="Enabled" EnableViewState="true" &gt;
  &lt;asp:ListItem Text="Select" Value="0"&gt;&lt;/asp:ListItem&gt;
  &lt;asp:ListItem Text="Email" Value="Email"&gt;&lt;/asp:ListItem&gt;
  &lt;asp:ListItem Text="SMS" Value="SMS"&gt;&lt;/asp:ListItem&gt;
  &lt;asp:ListItem Text="Voice SMS" Value="Voice SMS"&gt;&lt;/asp:ListItem&gt;
  &lt;/asp:DropDownList&gt;
  
  &lt;asp:UpdateProgress ID="UpdateProgress1" runat="server" AssociatedUpdatePanelID="UpdatePanel1"
  DisplayAfter="1"&gt;
  &lt;ProgressTemplate&gt;
  &lt;div id="IMGDIV" runat="server" align="center" style="visibility: visible; vertical-align: middle; position: absolute; background-color: #fafbf6"
  valign="middle"&gt;
   &lt;asp:Image ID="Image001" runat="server" ImageUrl="~/assets/img/ajax-loader.gif" /&gt;
   &lt;/div&gt;
   &lt;/ProgressTemplate&gt;
   &lt;/asp:UpdateProgress&gt;
  
     &lt;/ContentTemplate&gt;
  &lt;/asp:UpdatePanel&gt;
  </code></pre>
  
  <p>Code behind:</p>
  
  <pre><code>protected void ddl_TypeofCampaign_SelectedIndexChanged(object sender, EventArgs e)
  {
      Thread.Sleep(2000);
      FillTemplates();
      btn_Preview.Visible = false;
  
  }
  </code></pre>
  
  <p>My page Load code.</p>
  
  <pre><code>protected void Page_Load(object sender, EventArgs e)
  {
      if (!IsPostBack)
      {
          FillGrid();
          FillTypeofSourcing();
          FillCampaignNames();
          FillTemplates();
  
      }
  }
  </code></pre>
  
  <p>Fill Template method where I am getting templates name base on selection.</p>
  
  <pre><code> protected void FillTemplates()
  {
      if (ddl_TypeofCampaign.SelectedItem.ToString() != "Select")
      {
          bo.Para1 = ddl_TypeofCampaign.SelectedItem.ToString();
          bo.Para2 = "Stage1";//StageValue in TemplateMasterInfo Table
          DataTable dt = bl.Get_Templates(bo);
          ddl_TypeofTemplateName.DataSource = dt;
          ddl_TypeofTemplateName.DataTextField = "TemplateName";
          ddl_TypeofTemplateName.DataValueField = "TemplateId";
          ddl_TypeofTemplateName.Items.Clear();
          ddl_TypeofTemplateName.Items.Add(new ListItem("Select", "0"));
          ddl_TypeofTemplateName.DataBind();
      }
      else
      {
          ddl_TypeofTemplateName.Items.Clear();
          ddl_TypeofTemplateName.Items.Add(new ListItem("Select", "0"));
          ddl_TypeofTemplateName.DataBind();
      }
  }
  </code></pre>