Label background animation at runtime with WPF

Question

Hello, I would like to create programmatically an animation for the background color of a label but I have some problems.

I have implemented the following code:

  Public Sub DoBackgroundAnimation(ByVal obj As Label)

        If obj Is Nothing Then Return

        Dim animatedBrush As New SolidColorBrush()
        animatedBrush.Color = Colors.MidnightBlue

        Dim highlightAnimation As New ColorAnimation()
        highlightAnimation.[To] = Colors.Transparent
        highlightAnimation.Duration = TimeSpan.FromSeconds(1)
        Storyboard.SetTarget(highlightAnimation, animatedBrush)
        Storyboard.SetTargetProperty(highlightAnimation, New PropertyPath(SolidColorBrush.ColorProperty))

        Dim story As New Storyboard
        story.Children.Add(highlightAnimation)

        obj.Background = animatedBrush
        story.Begin(obj)

    End Sub

but nothing happens!

The background is simply colored MidnightBlue and no animation.

Do you have any suggestions?

Answer 1

I've seen exactly the same problem earlier today. But it was about render transfrom and in C#.

The short answer is to pass label as a target of animation, and change property path to (Label.Background).(SolidColorBrush.Color). The long answer involves playing with name scopes.

Hope this helps.

Cheers, Anvaka.

Answer 2

The problem I ran into last night (see here) was that using Storyboard.SetTarget only works when the property you're animating is a property of a FrameworkElement or FrameworkContentElement.

You're not actually animating Label.Background, you're animating SolidColorBrush.Color. So (at least, as I understand it) you must create a name scope, give your brush a name, and use Storyboard.SetTargetName to set it as a target.

This method works in C#; translating it to VB should be straightforward:

void AnimateLabel(Label label)
{
    // Attaching the NameScope to the label makes sense if you're only animating
    // things that belong to that label; this allows you to animate any number
    // of labels simultaneously with this method without SetTargetName setting
    // the wrong thing as the target.
    NameScope.SetNameScope(label, new NameScope());
    label.Background = new SolidColorBrush(Colors.MidnightBlue);
    label.RegisterName("Brush", label.Background);

    ColorAnimation highlightAnimation = new ColorAnimation();
    highlightAnimation.To = Colors.Transparent;
    highlightAnimation.Duration = TimeSpan.FromSeconds(1);

    Storyboard.SetTargetName(highlightAnimation, "Brush");
    Storyboard.SetTargetProperty(highlightAnimation, new PropertyPath(SolidColorBrush.ColorProperty));

    Storyboard sb = new Storyboard();
    sb.Children.Add(highlightAnimation);
    sb.Begin(label);
}