build method
Override this method to build widgets that depend on the state of the listenable (e.g., the current value of the animation).
Implementation
@override
Widget build(BuildContext context) {
final animation = listenable as Animation<double>;
return Visibility(
visible: animation.value != 0,
child: FadeTransition(
opacity: animation,
alwaysIncludeSemantics: alwaysIncludeSemantics,
child: child,
),
);
}