title: Set focus in TextBox after postback
body: <p>I have a simple page where I want to filter a ListBox based upon a value(s) in a textbox - both are in an UpdatePanel.<br>
  This works correctly, however, after the postback the textbox had lost focus...so I set focus back in the page_load.
  Then I noticed that the cursor was now at the beginning of the text when I want it at the end so the user can carry on typing, so I added an onfocus(...) attribute to the textbox to set the value back to itself (see code below).</p>
  
  <p>This works the first two times, but then it stops setting focus to the textbox?</p>
  
  <p><strong>Markup</strong></p>
  
  <pre><code>&lt;%@ Page Language="C#" AutoEventWireup="true" CodeBehind="ListTest.aspx.cs" Inherits="SalesForceTest.ListTest" %&gt;
  
  &lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"&gt;
  &lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;
  &lt;head runat="server"&gt;
      &lt;title&gt;&lt;/title&gt;
  &lt;/head&gt;
  &lt;body&gt;
      &lt;form id="form1" runat="server"&gt;
      &lt;div&gt;
          &lt;asp:ScriptManager ID="ScriptManager1" runat="server" LoadScriptsBeforeUI="true"/&gt;
          &lt;asp:UpdatePanel ID="UpdatePanel1" runat="server"&gt;
              &lt;ContentTemplate&gt;
                  &lt;asp:TextBox runat="server" ID="filter" AutoPostBack="true" onkeyup="__doPostBack(this.id, this.value)" onfocus="this.value = this.value;"  /&gt;
                  &lt;br /&gt;
                  &lt;asp:ListBox ID="AccountList" runat="server" Width="185px"&gt;&lt;/asp:ListBox&gt;
              &lt;/ContentTemplate&gt;
          &lt;/asp:UpdatePanel&gt;
      &lt;/div&gt;
      &lt;/form&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p><strong>Codebehind</strong></p>
  
  <pre><code>using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Web;
  using System.Web.UI;
  using System.Web.UI.WebControls;
  using System.Data;
  using System.Text;
  
  namespace SalesForceTest
  {
      public partial class ListTest : System.Web.UI.Page
      {
          List&lt;string&gt; allAccounts = new List&lt;string&gt; { "2342", "3434", "2332", "3224", "7899", "8797", "3435" };
  
          protected void Page_Load(object sender, EventArgs e)
          {
              AccountList.Items.Clear();
              allAccounts.Where(ac =&gt; ac.StartsWith(filter.Text)).ToList().ForEach(a =&gt; AccountList.Items.Add(a));
  
              if (Page.IsPostBack)
              {
                  if (Request.Form["__EVENTTARGET"] == filter.ID)
                  {
                      ScriptManager1.SetFocus(filter);
                  }
              }
          }
      }
  }
  </code></pre>
  
  <p>Any help <strong>VERY</strong> gratefully received :)</p>