Animations declared in code behind don't work

[Mopy18]

Describe the bug

I tried to implement this example from the documentation, but with the animation being declared in code behind instead of xaml. When I declare the animation in xaml like in the example it works as intended, but when it is declared in code behind nothing happens.

To Reproduce

So basically my UI has a Rectangle and a button, when the button is clicked it creates the animation and runs it:

var animation = new Animation();
animation.Duration = TimeSpan.FromSeconds(3);

animation.Children.Add(new KeyFrame
{
    Cue = new Cue(0.0),
    Setters =
    {
        new Setter { Property = Rectangle.OpacityProperty, Value = 0 },
    }
});

animation.Children.Add(new KeyFrame
{
    Cue = new Cue(1.0),
    Setters =
    {
        new Setter { Property = Rectangle.OpacityProperty, Value = 1 },
    }
});

await animation.RunAsync(Rect);

Nothing happens when I click the button, the opacity doesn't change at all. Note that if I run this code instead:

var animation = (Animation)this.Resources["ResourceAnimation"];
await animation.RunAsync(Rect);

it works as intended ("ResourceAnimation" being declared in xaml as done in the example).

I also tried animating different properties, using KeyTime instead of Cue, playing with Duration, PlaybackDirection, etc. Still nothing happens.

Expected behavior

No response

Avalonia version

11.1.0

OS

Windows, macOS

Additional context

No response

[maxkatz6]

OpacityProperty is a doable property, while you set an integer.
XAML compiler automatically converts this value, but C# is not.

Change Value = 0 and Value = 1 to Value = 0d and Value = 1d.

[maxkatz6]

Also, when running your code, I got InvalidCastException, which quickly helped me to find this issue. You can consider enabling all exceptions by default in IDE.

[Mopy18]

I feel dumb... Thank you for your time and answer!