Hello this is similar to http://stackoverflow.com/questions/2620165/how-to-access-a-named-element-of-a-derived-user-control-in-silverlight with the difference is inheriting from a templated control, not a user control.

I have a templated control called MyBaseControl

<Style TargetType="Problemo:MyBaseControl">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="Problemo:MyBaseControl">
                    <Grid x:Name="LayoutRoot" Background="White">
                        <Border Name="HeaderControl" Background="Red" />
                    </Grid>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

 public class MyBaseControl : Control
    {
        public UIElement Header { get; set; }

        public MyBaseControl()
        {   
            DefaultStyleKey = typeof(MyBaseControl);
        }

        public override void OnApplyTemplate()
        {
            base.OnApplyTemplate();

            var headerControl = GetTemplateChild("HeaderControl") as ContentPresenter;

            if (headerControl != null)
                headerControl.Content = Header;

        }
    }

I have another control called myControl which inherits from MyBaseControl Control

<me:MyBaseControl x:Class="Problemo.MyControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    xmlns:me="clr-namespace:Problemo" 
    d:DesignHeight="300" d:DesignWidth="400">
    <me:MyBaseControl.Header>
        <TextBlock Name="xxx" />
    </me:MyBaseControl.Header> 
</me:MyBaseControl>

public partial class MyControl : MyBaseControl { public string Text { get; set; }

public MyControl(string text)
{
    InitializeComponent();
    Text = text;
    Loaded += MyControl_Loaded;
}

void MyControl_Loaded(object sender, RoutedEventArgs e)
{
    base.ApplyTemplate();
    xxx.Text = Text;
}

}

The issue is xxx is null. How do I access the xxx control in the code behind ?