silverlight：ListBox中如何取得DateTemplate/ItemsPanelTemplate中的命名控件?

<UserControl x:Class="ToolsTest.Test"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Width="400" Height="300">
 <UserControl.Resources>
 <DataTemplate x:Key="dt">
 <TextBlock Padding="5,0,5,0"  Text="{Binding d}" x:Name="myTxt"/>
 </DataTemplate>
 </UserControl.Resources>
 <StackPanel>
 <ListBox Name="myListBox" ItemTemplate="{StaticResource dt}" /> 
 <Button Content="查找myTxt" x:Name="btnFind" Width="90" Click="btnFind_Click"></Button>
 </StackPanel>
</UserControl>

using System.Collections.ObjectModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;

namespace ToolsTest
{
 public partial class Test : UserControl
    {
        ObservableCollection<TestData> oc;

 public Test()
        {
            InitializeComponent();
 this.Loaded += new RoutedEventHandler(Test_Loaded);
        }

 void Test_Loaded(object sender, RoutedEventArgs e)
        {
            oc = new ObservableCollection<TestData>();
            oc.Add(new TestData() { d = "A" });
            oc.Add(new TestData() { d = "B" });
 this.myListBox.ItemsSource = oc;
        }       

 private void btnFind_Click(object sender, RoutedEventArgs e)
        {
 if (myListBox.SelectedItem != null)
            {
                ListBoxItem _selectedItem = (ListBoxItem)(myListBox.ItemContainerGenerator.ContainerFromItem(myListBox.SelectedItem));
                TextBlock myTxt = FindFirstVisualChild<TextBlock>(_selectedItem, "myTxt");
                MessageBox.Show(string.Format("选中行的TextBlock值为：" + myTxt.Text));
            }
 

            ListBoxItem _firstItem = (ListBoxItem)(myListBox.ItemContainerGenerator.ContainerFromItem(myListBox.Items[0]));

 //var t =  _firstItem.FindName("myTxt");//这样是找不到的
            TextBlock myTxtFirst = FindFirstVisualChild<TextBlock>(_firstItem, "myTxt");
            MessageBox.Show(string.Format("第一行的TextBlock值为：" + myTxtFirst.Text));
        }
 

 public T FindFirstVisualChild<T>(DependencyObject obj,string childName) where T : DependencyObject
        {
 for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
            {
                DependencyObject child = VisualTreeHelper.GetChild(obj, i);
 if (child != null && child is T && child.GetValue(NameProperty).ToString()==childName)
                {
 return (T)child;
                }
 else
                {
                    T childOfChild = FindFirstVisualChild<T>(child,childName);
 if (childOfChild != null)
                    {
 return childOfChild;
                    }
                }
            }
 return null;
        }
    }

 public class TestData{public string d{set;get;}}
}

<ListBox>
 <ItemsPanelTemplate>
 <StackPanel Orientation="Horizontal" x:Name="sp"></StackPanel>
 </ItemsPanelTemplate>
 
 <ListBox.ItemTemplate>
 <DataTemplate>
 <Rectangle Width="100" Height="100" Fill="{Binding Color}" x:Name="listItem" MouseLeftButtonDown="listItem_MouseLeftButtonDown"></Rectangle>
 </DataTemplate>
 </ListBox.ItemTemplate>
 </ListBox>

 StackPanel _sp = null;
 private void sp_Loaded(object sender, RoutedEventArgs e)
 {
     _sp = sender as StackPanel;
 }