Changing Position of an Element Programmatically in WPF

I did not knew that this simple thing would be slightly complicated. I have a Canvas in which I am trying to add Ellipse dynamically. Here is the code: ``` <StackPanel> <Canvas Name="canvas" Background="LightBlue" Margin="5" Width="250" Height="250"> </Canvas> <Button Content="Draw Images" Click="Button_Click" Width="100" Margin="10" /> </StackPanel> ``` And here is the code behind: ``` private void Button_Click(object sender, RoutedEventArgs e) { Ellipse ellipse = new Ellipse(); ellipse.Fill = Brushes.Red; ellipse.Width = 10; ellipse.Height = 10; ellipse.SetValue(Canvas.LeftProperty,100); ellipse.SetValue(Canvas.TopProperty,100); canvas.Children.Add(ellipse); } ``` For some reason it throws the exception that 100 is not a valid value!