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 >