如何在silverlight中以编程方式在画布中添加UI元素

我在网格内有一个画布。我想动态添加控件（文本块和图像）。我正在使用以下代码，但它没有显示任何内容。

XAML:

<Grid x:Name="BaseGrid"
              Background="White"
              Grid.Row="2">
    <Canvas x:Name="RootCanvas"
            HorizontalAlignment="Stretch"
            VerticalAlignment="Stretch"
            Visibility="Collapsed"
            Canvas.ZIndex="0">
        <Canvas x:Name="BaseCanvas"
                CacheMode="BitmapCache"
                HorizontalAlignment="Center"
                VerticalAlignment="Center"
                Canvas.Left="0"
                Canvas.Top="0"
                Canvas.ZIndex="0">
            <Canvas.Clip>
                <RectangleGeometry x:Name="BaseCanvasClip"/>
            </Canvas.Clip>
            <Canvas x:Name="DrawingCanvas"
                    HorizontalAlignment="Center"
                    VerticalAlignment="Center"
                    Canvas.Left="0"
                    Canvas.Top="0"
                    Canvas.ZIndex="10">
            </Canvas>
            <Canvas x:Name="TransparentCanvas"
                    Background="Transparent"
                    HorizontalAlignment="Center"
                    VerticalAlignment="Center"
                    Canvas.Left="0"
                    Canvas.Top="0"
                    Canvas.ZIndex="100"
                    Visibility="Collapsed">
            </Canvas>
        </Canvas>
    </Canvas>
    </Grid>
</Grid>

代码：

TextBlock txtBlk = new TextBlock();
txtBlk.FontSize = 14;
txtBlk.Foreground = new SolidColorBrush(Colors.Red);
txtBlk.Text = CreateConceptTextBox.Text;
Canvas.SetTop(txtBlk, 100);
Canvas.SetLeft(txtBlk, 450);
//Grid.SetRow(txtBlk, 100);
//Grid.SetColumn(txtBlk, 450);
linkDiscovery.DrawingCanvas.Children.Add(txtBlk);

我关心"绘画画布"。我在这里缺了什么？