How to create a Silverlight popup with a TextBox populate its parent?

Question

I have a popup in a user control. A popup window uses a TextBox to display a textual preview of the data generated by the control.

How to make the size of the popup window the user controlling it inside? With the code as shown below, I found that the text field is sized according to its contents, and the pop-up window is sized according to the text field.

It works fine if I use fixed sizes in row and column definitions, but I would like to pop up to resize it to fit the user control (which in turn matches the browser).

<UserControl
  <!-- usual stuff here -->
>
<Grid>

<!-- layout for the user control here -->
<!-- and after that my popup: -->
<Popup Name="MyPopup">
   <Border BorderBrush="Black" BorderThickness="2" >
      <Grid>
         <Grid.RowDefinitions>
            <RowDefinition Height="22"></RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
         </Grid.RowDefinitions>
         <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"></ColumnDefinition>
         </Grid.ColumnDefinitions>

         <TextBlock Grid.Row="0" Text="Preview:" Margin="5" ></TextBlock>
         <TextBox 
              Grid.Row="1"
              Name="MyTextBox" 
              IsReadOnly="True"
              HorizontalScrollBarVisibility="Visible"
              VerticalScrollBarVisibility="Visible"
              TextWrapping="Wrap"
              Margin="5"
              >
          </TextBox>
      </Grid>
  </Border>
</Popup>

</Grid></UserControl>

Answer 1

# :

    textBox1.Width = UserControl.Width;
    textBox1.Height = UserControl.Height;
    textBox1.Margin = UserControl.Margin;

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