Анимация. Проблема с кодом или что-то еще? Visual studio, WPF, C#, xaml

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здравствуйте, пожалуйста, этот код показывает анимированный прямоугольник, я не вижу анимации, интересно, что может быть причиной

<pre lang="c#">
// Demonstrates the From and To properties used together.

// Create a NameScope for this page so that
// Storyboards can be used.
NameScope.SetNameScope(this, new NameScope());

Rectangle myRectangle = new Rectangle();

// Assign the Rectangle a name so that
// it can be targeted by a Storyboard.
this.RegisterName(
    "fromToAnimatedRectangle", myRectangle);
myRectangle.Height = 10;
myRectangle.Width = 100;
myRectangle.HorizontalAlignment = HorizontalAlignment.Left;
myRectangle.Fill = Brushes.Black;

// Demonstrates the From and To properties used together.
// Animates the rectangle's Width property from 50 to 300 over 10 seconds.
DoubleAnimation myDoubleAnimation = new DoubleAnimation();
myDoubleAnimation.From = 50;
myDoubleAnimation.To = 300;
myDoubleAnimation.Duration =
    new Duration(TimeSpan.FromSeconds(10));

Storyboard.SetTargetName(myDoubleAnimation, "fromToAnimatedRectangle");
Storyboard.SetTargetProperty(myDoubleAnimation,
    new PropertyPath(Rectangle.WidthProperty));
Storyboard myStoryboard = new Storyboard();
myStoryboard.Children.Add(myDoubleAnimation);

// Use an anonymous event handler to begin the animation
// when the rectangle is clicked.
myRectangle.MouseLeftButtonDown += delegate(object sender, MouseButtonEventArgs args)
    {
        myStoryboard.Begin(myRectangle);

    };

код XAML

<!-- Demonstrates the From and To properties used together. -->
<Rectangle Name="fromToAnimatedRectangle"

   Height="10" Width="100" HorizontalAlignment="Left"

   Fill="Black">
  <Rectangle.Triggers>
    <EventTrigger RoutedEvent="Rectangle.MouseLeftButtonDown">
      <BeginStoryboard>
        <Storyboard>
        <!-- Demonstrates the From and To properties used together.
               Animates the rectangle's Width property from 50 to 300 over 10 seconds. -->
        <DoubleAnimation 

          Storyboard.TargetName="fromToAnimatedRectangle" 

          Storyboard.TargetProperty="Width"

          From="50" To="300" Duration="0:0:10" />
        </Storyboard>
      </BeginStoryboard>
    </EventTrigger>
  </Rectangle.Triggers>
</Rectangle>

Что я уже пробовал:

код XAML:

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