Question

why does it not work the way it should? There is no movement…. below is the code:

namespace MovingBox
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        Storyboard myStoryboard = new Storyboard();

        public MainWindow()
        {
            InitializeComponent();

        }

        private void Start_Animation(object sender, EventArgs e)
        {
            myStoryboard.Begin();
        }

        private void MyAnimatedRectangle_MouseDown(object sender, MouseButtonEventArgs e)
        {
            Start_Animation(sender, e); 
        }
    }
}

XAML:

<Window x:Class="MovingBox.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">



<Grid>
    <StackPanel>
        <StackPanel.Resources>
            <Storyboard x:Name="myStoryboard" x:Key="myStoryboardKey">
                <DoubleAnimation
      Storyboard.TargetName="MyAnimatedRectangle"
      Storyboard.TargetProperty="Opacity"
      From="1.0" To="0.0" Duration="0:0:5" 
      AutoReverse="True" RepeatBehavior="Forever" />
            </Storyboard>
        </StackPanel.Resources>

        <Rectangle Loaded="Start_Animation" x:Name="MyAnimatedRectangle"
 Width="100" Height="100" Fill="Blue" MouseDown="MyAnimatedRectangle_MouseDown" />

    </StackPanel>
</Grid>

Answer 1

The myStoryBoard you are referring to in the Start_Animation method is a different one from the one in the XAML.

Here’s a working version that searches for the storyboard resource:
Note that I removed the Storyboard myStoryboard = new Storyboard();

private void MyAnimatedRectangle_MouseDown(object sender, MouseButtonEventArgs e)
{
    PlayMyStoryboard(sender as FrameworkElement);
}

private void PlayMyStoryboard(FrameworkElement sender)
{
    var sb = sender.FindResource("myStoryboardKey") as Storyboard;
    if (sb != null)
    {
        sb.Begin();
    }
}

private void Start_Animation(object sender, RoutedEventArgs e)
{
    PlayMyStoryboard(sender as FrameworkElement);
}