InheritedNotifier example

main.dart

// Flutter code sample for

// This example shows three spinning squares that use the value of the notifier
// on an ancestor [InheritedNotifier] (`SpinModel`) to give them their
// rotation. The notifier doesn't need to know about the children, or need to
// be an animation controller, however. The `SpinModel` class could just as
// easily listen to another object (say, a separate object that keeps the
// value of a slider) that was a [Listenable], and get the value from that. The
// descendants also don't need to have an instance of the [InheritedNotifier]
// in order to use it, they just need to know that there is one in their
// ancestry. This can help with decoupling widgets from their models.

import 'package:flutter/material.dart';

import 'dart:math' as math;

void main() => runApp(MyApp());

/// This Widget is the main application widget.
class MyApp extends StatelessWidget {
  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Material(child: MyStatefulWidget()),
    );
  }
}

class SliderInfo extends ChangeNotifier {
  SliderInfo();

  double get value => _value;
  double _value = 0.0;
  set value(double value) {
    if (value != _value) {
      _value = value;
      notifyListeners();
    }
  }
}

class SliderNotifier extends InheritedNotifier<SliderInfo> {
  SliderNotifier({
    Key key,
    SliderInfo notifier,
    Widget child,
  }) : super(key: key, notifier: notifier, child: child);

  static double of(BuildContext context) {
    return context.dependOnInheritedWidgetOfExactType<SliderNotifier>().notifier.value;
  }
}

class Spinner extends StatelessWidget {
  const Spinner();

  @override
  Widget build(BuildContext context) {
    return Transform.rotate(
      angle: SliderNotifier.of(context) * 2.0 * math.pi,
      child: Container(
        width: 100,
        height: 100,
        color: Colors.green,
        child: const Center(
          child: Text('Whee!'),
        ),
      ),
    );
  }
}

SliderInfo sliderInfo = SliderInfo();

class MyStatefulWidget extends StatefulWidget {
  MyStatefulWidget({Key key}) : super(key: key);

  @override
  _MyStatefulWidgetState createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> with TickerProviderStateMixin {
  AnimationController _controller;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      duration: const Duration(seconds: 10),
      vsync: this,
    )..repeat();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return SliderNotifier(
      notifier: sliderInfo,
      child: Builder(builder: (BuildContext context) {
        return Column(
          children: <Widget>[
            Slider(
              min: 0.0,
              max: 1.0,
              value: SliderNotifier.of(context),
              onChanged: (double value) {
                sliderInfo.value = value;
              },
            ),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceAround,
              children: const <Widget>[
                Spinner(),
                Spinner(),
                Spinner(),
              ],
            ),
          ],
        );
      }),
    );
  }
}