[v1.x only] Getting reference to controls inside tabstrip templates

HOW-TO
Get reference to controls inside tabstrip templates (v1.x only)

SOLUTION
When you have server controls nested inside a RadTabStrip template you cannot directly access them in the code-behind. If you have the following set-up:

<radTS:RadTabStrip ID="RadTabStrip1" Runat="server">
<TabCollection>
  <radTS:Tab ID="Tab1" Text="Tab 1">
    <ContentTemplate>
    <asp:TextBox ID="TextBox1" Runat="server" Text="Text 1 Text"></asp:TextBox>
    </ContentTemplate>
  </radTS:Tab>
  <radTS:Tab ID="Tab2" Text="Tab 2">
    <ContentTemplate>
    <asp:TextBox ID="TextBox2" Runat="server" Text="Text 2 Text"></asp:TextBox>
    </ContentTemplate>
  </radTS:Tab>
</TabCollection>
</radTS:RadTabStrip>

then if you try the following in your code-behind:

protected Telerik.WebControls.RadTabStrip RadTabStrip1;
protected System.Web.UI.WebControls.TextBox TextBox1;

private void Page_Load(object sender, System.EventArgs e)
{
  TextBox1.Text = "Set from code-behind";
}

you will get a System.NullReferenceException exception.

In order to properly access a control inside a template you must use the RadTabStrip's FindControl() method. So the upper function should become like this:

The FindControl() method returns a reference to a Control class so you must properly typecast the returned value to the class you need.

For more information refer to the FindControl method in the RadTabStrip API reference.