Animation<T>.fromValueListenable constructor Null safety

Animation<T>.fromValueListenable(
  1. ValueListenable<T> listenable,
  2. {ValueListenableTransformer<T>? transformer}
)

Create a new animation from a ValueListenable.

The returned animation will always have an animations status of AnimationStatus.forward. The value of the provided listenable can be optionally transformed using the transformer function.

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This constructor can be used to replace instances of ValueListenableBuilder widgets with a corresponding animated widget, like a FadeTransition.

Before: 

Widget build(BuildContext context) {
  return ValueListenableBuilder<double>(
    valueListenable: _scrollPosition,
    builder: (BuildContext context, double value, Widget? child) {
      final double opacity = (value / 1000).clamp(0, 1);
      return Opacity(opacity: opacity, child: child);
    },
    child: Container(
      color: Colors.red,
      child: const Text('Hello, Animation'),
    ),
  );
}

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After: 
Widget build2(BuildContext context) {
  return FadeTransition(
    opacity: Animation<double>.fromValueListenable(_scrollPosition, transformer: (double value) {
      return (value / 1000).clamp(0, 1);
    }),
    child: Container(
      color: Colors.red,
      child: const Text('Hello, Animation'),
    ),
  );
}

Implementation

factory Animation.fromValueListenable(ValueListenable<T> listenable, {
  ValueListenableTransformer<T>? transformer,
}) = _ValueListenableDelegateAnimation<T>;