How to rename a button with double click

I have a button with a custom template. Do you have any idea how I can rename the content in the button with a double click. This is what I have, but from code I cannot access b1.textBox to set the visibility to visible.

 <Window.Resources>
    <Style TargetType="{x:Type Button}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="Button">
      开发者_C百科              <Grid>
                        <Ellipse x:Name="outerCircle"  Fill="Red" Height="50" Width="50"/>
                        <Ellipse x:Name="innerCircle" Fill="White" RenderTransformOrigin=".5,.5">
                            <Ellipse.RenderTransform>
                                <ScaleTransform ScaleX=".9" ScaleY=".9"/>
                            </Ellipse.RenderTransform>
                        </Ellipse>
                        <Grid>
                            <ContentPresenter HorizontalAlignment="Center" VerticalAlignment="Center"/>
                            <TextBox x:Name="textBox" Visibility="Collapsed"/>

                        </Grid>

                    </Grid>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</Window.Resources>

---

 void button1_MouseDoubleClick(object sender, MouseButtonEventArgs e)
    {
        //MessageBox.Show(e.Source.ToString());
        Button b1 = (Button)e.Source;
       // b1.textBox doesn't get displayed here.
    }

---

what about

b1.Template.FindName("textBox",b1) as TextBox

?

---

Why not just add this to the style?
<EventSetter Event="MouseDoubleClick" Handler="HandleDoubleClick" />

Then in code behind:

protected void HandleDoubleClick(object sender, MouseButtonEventArgs e)  
{  
  Button b1 = (Button)sender;
}