title: Enable tabpanel in tabcontainer
body: <p>I have a tabcontainer with two tabs. The first tab contains a textbox, while the second tab contains a panel.</p>
  
  <p>I want the second tab to be disabled at first page load, and I want it to become enabled as soon as the user enters an input in the textbox in tab1. When textbox in tab1 is emptied again, the second tab should again be disabled.</p>
  
  <p>I tried the following code, but the second tab remains disabled no matter what.
  Any help would be appreciated. Thank you!</p>
  
  <p><strong>aspx</strong></p>
  
  <pre><code>&lt;asp:TabContainer ID="TabContainer1" runat="server" ActiveTabIndex="4" HeaderText=""
      Height="578px" Width="900px" TabStripPlacement="Top" ScrollBars="None" UseVerticalStripPlacement="false"
      VerticalStripWidth="120px" BackColor="White" BorderColor="White" Style="margin-right: 84px"&gt;
      &lt;asp:TabPanel ID="TabPanel1" runat="server"&gt;
          &lt;HeaderTemplate&gt;
              General
          &lt;/HeaderTemplate&gt;
          &lt;ContentTemplate&gt;
               &lt;asp:UpdatePanel ID="TestUpdatePanel" runat="server"&gt;
                  &lt;ContentTemplate&gt;
                          &lt;table style="height: 247px; width: 100%;"&gt;
                              &lt;tr&gt;
                                    &lt;td&gt;
                                         &lt;asp:TextBox ID="HorizonTextBox" runat="server" OnTextChanged="HorizonTextBox_TextChanged"
                                                      AutoPostBack="True"&gt;&lt;/asp:TextBox&gt;
                                    &lt;/td&gt;
                              &lt;/tr&gt;
                           &lt;/table&gt;
                  &lt;/ContentTemplate&gt;
               &lt;/asp:UpdatePanel&gt;
          &lt;ContentTemplate&gt;
       &lt;/asp:TabPanel&gt;
       &lt;asp:TabPanel ID="TabPanel2" runat="server"&gt;
           &lt;HeaderTemplate&gt;
              Dashboard
          &lt;/HeaderTemplate&gt;
          &lt;ContentTemplate&gt;
              &lt;asp:Button ID="RunSimulationButton" runat="server" Text="Run Simulation" OnClick="RunSimulationButton_OnClick" /&gt;
              &lt;br /&gt;
              &lt;br /&gt;
              &lt;asp:Panel ID="PlotPanel" runat="server"&gt;
              &lt;/asp:Panel&gt;
          &lt;/ContentTemplate&gt;
      &lt;/asp:TabPanel&gt;
  </code></pre>
  
  <p><strong>aspx.cs</strong></p>
  
  <pre><code>    protected void Page_Load(object sender, EventArgs e)
      {
          if (!Page.IsPostBack)
          {
              TabContainer1.ActiveTabIndex = 0;
  
              TabPanel2.Enabled = false;
  
          }
      }
  
      protected void HorizonTextBox_TextChanged(object sender, EventArgs e)
      {
          if(HorizonTextBox.Text != "")
          {
                TabPanel2.Enabled = true;
          }
      }
  </code></pre>