Silverlight下TextBlock文字居中对齐的实现

.xaml

<Canvas
    xmlns="http://schemas.microsoft.com/client/2007"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Width="640" Height="480"
    Background="White"
    x:Name="Page"
    >
  <Canvas Width="50" Height="26" x:Name="Do_Button" Canvas.Left="35" Canvas.Top="11">
    <Rectangle Width="50" Height="26" Stroke="#FF212121" RadiusX="5" RadiusY="5" StrokeThickness="2" x:Name="RecProgressBg">
      <Rectangle.Fill>
        <LinearGradientBrush EndPoint="0.5,1.167" StartPoint="0.5,-0.333">
          <GradientStop Color="#0A0809" Offset="0"/>
          <GradientStop Color="#0A0809" Offset="1"/>
          <GradientStop Color="#666666" Offset="0.572"/>
          <GradientStop Color="#0A0809" Offset="0.572"/>
        </LinearGradientBrush>
      </Rectangle.Fill>
    </Rectangle>
    <TextBlock x:Name="txtProgress" Width="100" Height="26" Canvas.Left="6" Canvas.Top="3" TextWrapping="NoWrap">
    </TextBlock>
  </Canvas>  
</Canvas>

.xaml.js

        var txtProgress=rootElement.findName("txtProgress");
        txtProgress.foreground="white";
        txtProgress.Text ="4/5";
        txtProgress.FontSize="12";
        txtProgress.FontWeight="Thin";
        var RecProgressBg=rootElement.findName("RecProgressBg");
        txtProgress.SetValue("Canvas.Left",(RecProgressBg.Width-txtProgress.ActualWidth)/2);//居中对齐实现