Dynamically adding and moving ellipses using WPF - wpf

Question

I'm using WPF and having trouble dynamically/programatically adding ellipses to my grid.
I'm dynamically allocating and placing ellipses inside myGrid. Trouble is the position on the ellipses don't change. I'm using Canvas.SetLeft and SetTop, but the ellipses still seem stuck.
Here is the code for dynamic allocation :
{
...
Ellipse el = new Ellipse();
RadialGradientBrush b = new RadialGradientBrush();
b.RadiusX = r * 10.0f;
b.RadiusY = r * 10.0f;
b.GradientOrigin = new Point(0.5f, 0.5f);
b.GradientOrigin = new Point(0.5f, 0.5f);
b.GradientStops.Add(new GradientStop(Colors.Green, 0.0));
b.GradientStops.Add(new GradientStop(Colors.Blue, 1.0));
el.Width = 5.0f + r * 20.0f;
el.Height = 5.0f + r * 20.0f;
el.Stroke = b;
SetEllipsePosition(el, p);
this.myGrid.Children.Add(el);
...
}
private void SetEllipsePosition(FrameworkElement ellipse, Point j)
{
Canvas.SetLeft(ellipse, j.X);
Canvas.SetTop(ellipse, j.Y);
}
<Grid Height="480" Name="myGrid" Width="640">
<GroupBox Header="Pattern" Height="117" HorizontalAlignment="Left" Margin="10,564,0,0" Name="groupBox1" VerticalAlignment="Top" Width="238"></GroupBox>
<Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="33,30,0,0" Name="button1" VerticalAlignment="Top" Width="75" Click="button1_Click_1" />
<Grid Margin="6,507,408,-121">
<RadioButton Content="Lines" Height="16" HorizontalAlignment="Left" Margin="15,18,0,0" Name="rbLines" VerticalAlignment="Top" GroupName="RenderStyles" />
<RadioButton Content="Circles" Height="16" HorizontalAlignment="Left" Margin="15,49,0,0" Name="rbCircles" VerticalAlignment="Top" GroupName="RenderStyles" />
</Grid>
</Grid>

Answer 1

The problem is that you are using a Grid but setting Canvas properties, you could add a Canvas into the Grid and draw you ellipses on the Canvas ( add them to the Canvases children), and then it would work.
Or you could use the Margin property of your ellipse to set it's position on the Grid

Answer 2

Canvas.Left and Canvas.Top are attached properties: you set them only if your UI element is going to be contained in a Canvas; and only when it is on a Canvas will those properties be used (by the Canvas layout manager). Same with attached properties from Grid (such as Grid.Column to tell the Grid parent in what column the UI elements "wants" to be), Panel (Panel.ZIndex to tell the Panel parent at what z index the UI element should be put), etc.