<Grid>

<Grid HorizontalAlignment="Center" VerticalAlignment="Center" x:Name="g">

<Canvas>

<Rectangle RadiusX="5" RadiusY="5"

Width="{Binding ElementName=g, Path=ActualWidth}"

Height="{Binding ElementName=g, Path=ActualHeight}"

Stroke="Blue" StrokeDashArray="5,2,1,2" StrokeThickness="2"/>

</Canvas>

<TextBlock Margin="10,7,10,7" Text="aaa" HorizontalAlignment="Center" VerticalAlignment="Center"/>

</Grid>

</Grid>

效果图：

 

公共样式：

1 

使用示例：

<ContentControl Margin="10" HorizontalAlignment="Center" VerticalAlignment="Center"

BorderThickness="2" BorderBrush="Blue" Style="{StaticResource myBorder}">

<TextBlock Text="abc"/>

</ContentControl>