import 'package:flutter/material.dart';
class InheritedProvider<T> extends InheritedWidget {
  final T data;
  InheritedProvider({@required this.data, Widget child}) : super(child: child);
  @override
  bool updateShouldNotify(InheritedProvider<T> oldWidget) {
    //在此簡單返回true，則每次更新都會調用依賴其的子孫節點的 didChangeDependencies
    return true;
  }
}

class ChangeNotifierProvider<T extends ChangeNotifier> extends StatefulWidget {
  final Widget child;
  final T data; //共享的數據模型，要求繼承ChangeNotifier
  const ChangeNotifierProvider({
    Key key,
    this.child,
    this.data,
  }) : super(key: key);
  ///提供方法，子樹獲取共享數據
  static T of<T>(BuildContext context) {
    final provider =
        context.dependOnInheritedWidgetOfExactType<InheritedProvider<T>>();
    return provider.data;
  }
  @override
  _ChangeNotifierProviderState createState() =>
      _ChangeNotifierProviderState<T>();
}
class _ChangeNotifierProviderState<T extends ChangeNotifier>
    extends State<ChangeNotifierProvider<T>> {
  ///如果數據發生變化（model類調用 notifyListeners）,重新構建InheritedProvider
  void update() {
    setState(() => {});
  }
  @override
  void didUpdateWidget(ChangeNotifierProvider<T> oldWidget) {
    ///當Provider更新時，如果新舊數據不"=="，則解綁舊數據監聽，同時添加新數據監聽
    if (widget.data != oldWidget.data) {
      oldWidget.data.removeListener(update);
      widget.data.addListener(update);
    }
    super.didUpdateWidget(oldWidget);
  }
  @override
  void initState() {
    widget.data.addListener(update);
    super.initState();
  }
  @override
  void dispose() {
    widget.data.removeListener(update);
    super.dispose();
  }
  @override
  Widget build(BuildContext context) {
    return InheritedProvider<T>(
      data: widget.data,
      child: widget.child,
    );
  }
}

///響應數據變化的消費者
class NotifyConsumer<T> extends StatelessWidget {
  final Widget Function(BuildContext context, T value) builder;
  const NotifyConsumer({Key key, @required this.builder}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return builder(
      context,
      ChangeNotifierProvider.of<T>(context),
    );
  }
}

///共享數據模型
class CountModel extends ChangeNotifier {
  int _count = 0;
  int get count => _count;
  //提供自增方法
  void increase() {
    _count++;
    // 通知監聽器（訂閱者），重新構建InheritedProvider， 更新狀態。
    notifyListeners();
  }
}

import 'package:flutter/material.dart';
import 'package:test_interited/provider/change_notifier_provider.dart';
import 'package:test_interited/provider/notify_consumer.dart';
import 'package:test_interited/provider/test/count_model.dart';
class TestNotifierWidget extends StatefulWidget {
  const TestNotifierWidget({Key key}) : super(key: key);
  @override
  _TestNotifierWidgetState createState() => _TestNotifierWidgetState();
}
class _TestNotifierWidgetState extends State<TestNotifierWidget> {
  @override
  Widget build(BuildContext context) {
    return Center(
        child: ChangeNotifierProvider<CountModel>(
            data: CountModel(),
            child: Builder(builder: (context) {
              return Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  Builder(
                    builder: (context) {
                      //獲取共享數據源
                      return NotifyConsumer<CountModel>(
                          builder: (context, value) {
                        return Text(value.count.toString());
                      });
                    },
                  ),
                  Builder(builder: (context) {
                    return RaisedButton(
                      child: Text('自增'),
                      onPressed: () {
                        //獲取共享model，進行數據自增操作
                        ChangeNotifierProvider.of<CountModel>(context).increase();
                      },
                    );
                  }),
                ],
              );
            })));
  }
}