ControlTemplate 和 DataTemplate 都是派生自FrameworkTemplate， 这个类有 FindName 方法 访问内部的控件
也就是说只有我们获得了Template 就可以访问内部控件。
对于ControlTemplate，访问控件的Template属性即可。但是对于 DataTemplate 则要麻烦一些
1、访问 ControlTemplate 内部控件
<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";
}