ControlTemplate 和 DataTemplate 都是派生自FrameworkTemplate， 這個類有 FindName 方法 訪問內部的控制元件

也就是說只有我們獲得了Template 就可以訪問內部控制元件。

對於ControlTemplate，訪問控制元件的Template屬性即可。但是對於 DataTemplate 則要麻煩一些

1、訪問 ControlTemplate 內部控制元件

<Window.Resources>
        <ControlTemplate x:Key="ctemp">
            <StackPanel Background="Orange">
                <TextBlock x:Name="t1" Margin="6" Background="White"></TextBlock>
                <TextBlock x:Name="t2" Margin="6,6" Background="White"></TextBlock>
                <TextBlock x:Name="t3" Margin="6" Background="White"></TextBlock>
            </StackPanel>
        </ControlTemplate>
    </Window.Resources>
    <StackPanel Background="Yellow">
        <UserControl x:Name="uc" Template="{StaticResource ctemp}" Margin="5"></UserControl>
        <Button Content="Find by Name" Click="Button_Click"></Button>
    </StackPanel>

private void Button_Click(object sender, RoutedEventArgs e)
        {
            TextBlock tb = this.uc.Template.FindName("t1", this.uc) as TextBlock;
            tb.Text = "Hello Wpf";
            StackPanel sp=tb.Parent as StackPanel;
            var tb2=sp.Children[1] as TextBlock;
            var tb3=sp.Children[2] as TextBlock;

            tb2.Text="Control Template";
            tb3.Text= "I Can Find you";
        }