WPF 寻找数据模板中的元素

<Window x:Class="Wpf180706.Window11"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:Wpf180706"
        Title="Window11" Height="300" Width="300">
    <Window.Resources>
        <local:Person x:Key="person" Id="1" Name="zhangsan" Skill="wpf"></local:Person>
        <DataTemplate x:Key="tpl">
            <Border BorderBrush="Orange" BorderThickness="3" CornerRadius="5">
                <StackPanel>
                    <TextBlock Text="{Binding Id}"></TextBlock>
                    <TextBlock Name="tb2" Text="{Binding Name}"></TextBlock>
                    <TextBlock Text="{Binding Skill}"></TextBlock>
                </StackPanel>
            </Border>
        </DataTemplate>
    </Window.Resources>
    <Grid>
        <StackPanel>
        <ContentPresenter Name="cp" Content="{StaticResource person}" ContentTemplate="{StaticResource tpl}"></ContentPresenter>
        <Button Click="btn_Click">btn</Button>
        </StackPanel>
    </Grid>

</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;


namespace Wpf180706
{
    /// <summary>
    /// Interaction logic for Window11.xaml
    /// </summary>
    public partial class Window11 : Window
    {
        public Window11()
        {
            InitializeComponent();
        }


        private void btn_Click(object sender, RoutedEventArgs e)
        {
           TextBlock tb =  (TextBlock)this.cp.ContentTemplate.FindName("tb2", this.cp);
           MessageBox.Show(tb.Text);
        }


    }


    public class Person
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Skill { get; set; }
    }
}