title: updatepanel trigger cause fullpostback instead partial postback
body: <p>I want partial postback(asyncpostback) instead fullpostback.but it's not working.  Dynamically created checkbox where check or unchecked checkbox cause fullpostback
  but it should be asyncpostback.Here is my code.....</p>
  
  <pre><code>&lt;asp:CheckBoxList ID="chkList" runat="server" AutoPostBack="true" OnSelectedIndexChanged="chkList_SelectedIndexChanged"
                  ClientIDMode="AutoID"&gt;
              &lt;/asp:CheckBoxList&gt;
  
  &lt;asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional"&gt;
                  &lt;ContentTemplate&gt;
  
                      &lt;asp:Label ID="lblMessage" runat="server" Visible="false"&gt;&lt;/asp:Label&gt;
                  &lt;/ContentTemplate&gt;
                  &lt;Triggers&gt;
                      &lt;asp:AsyncPostBackTrigger ControlID="chkList" EventName="SelectedIndexChanged" /&gt;
                  &lt;/Triggers&gt;
              &lt;/asp:UpdatePanel&gt;
  </code></pre>
  
  <p>C# code:</p>
  
  <pre><code>private static readonly string constring = ConfigurationManager.ConnectionStrings["ConnectionStrRead"].ToString();
  
      protected void Page_Load(object sender, EventArgs e)
      {
        if (!IsPostBack)
          {
              SqlConnection con = new SqlConnection(constring);
              SqlCommand com = new SqlCommand("Select * from Category");
              com.Connection = con;
              con.Open();
              SqlDataAdapter da = new SqlDataAdapter(com);
              DataTable dt = new DataTable();
              da.Fill(dt);
  
              int dtRows = dt.Rows.Count;
              List&lt;string&gt; itemList = new List&lt;string&gt;();
              for (int i = 0; i &lt; dtRows; i++)
              {
                  //itemList = new List&lt;string&gt;();
                  string item = dt.Rows[i]["CategoryName"].ToString() + "(" + dt.Rows[i]["CreateUser"].ToString() + ")";
                  itemList.Add(item);
              }
              chkList.DataSource = itemList.ToArray();
              chkList.DataBind();
              con.Close();
          }
      }
  
   protected void chkList_SelectedIndexChanged(object sender, EventArgs e)
      {
          lblMessage.Visible = true;
          lblMessage.Text = string.Empty;
          foreach (ListItem item in chkList.Items)
          {
              if (item.Selected)
              {
                  lblMessage.Text += item.Text + "&lt;br/&gt;";
              }
          }
      }
  </code></pre>