WPF：重写了TabControl的模板，为什么FindName找不到控件？


        <Style  TargetType="{x:Type TabControl}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type TabControl}">
                        <Grid>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="Auto"></RowDefinition>
                                <RowDefinition></RowDefinition>
                            </Grid.RowDefinitions>
                            <TabPanel Grid.Row="0" Panel.ZIndex="1"  Margin="5,0,0,0" IsItemsHost="True"></TabPanel>
                            <Border Name="Borderl" Grid.Row="1" Background="#ffff0000" BorderBrush="#FF999999" BorderThickness="1" Padding="2">
                                <ContentPresenter ContentSource="SelectedContent" ></ContentPresenter>
                            </Border>
                        </Grid>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>if(this.tabControl.FindName("Border1")==null)
{
   this.Title="NULL";
}
else
{
  this.Title="Finded";
}为什么this.tabControl.FindName("Border1")，是空的？模板里分明是有Border1的啊