WPF

public static class Animations
{
    static Animations()
    {
    }

    public static void Fade(this UIElement control, double sourceOpacity, double targetOpactity, int milliseconds)
    {
        control.BeginAnimation(UIElement.OpacityProperty,
          new DoubleAnimation(sourceOpacity,targetOpactity,
          new Duration(TimeSpan.FromMilliseconds(milliseconds))));
    }
}