import 'package:flutter/material.dart';
class InheritedShareWidget extends InheritedWidget {
  //用于共享的數據
  final int data;
  InheritedShareWidget({this.data, Widget child}) : super(child: child);
  //定義便捷方法，方便子控件獲取共享數據
  static InheritedShareWidget of(BuildContext context) {
    ///當子控件依賴使用了我們的數據源時，數據變動會觸發子控件中的 didChangeDependencies 方法
    return context.dependOnInheritedWidgetOfExactType<InheritedShareWidget>();
    ///（前提：子控件使用了數據源）子控件中的 didChangeDependencies 方法不會被觸發
    // return context.getElementForInheritedWidgetOfExactType<InheritedShareWidget>().widget;
  }
  @override
  bool updateShouldNotify(covariant InheritedShareWidget oldWidget) {
    //返回true時，才會通知子控件
    return oldWidget.data != this.data;
  }
}

class TestShareChildWidget extends StatefulWidget {
  const TestShareChildWidget({Key key}) : super(key: key);
  @override
  _TestShareChildWidgetState createState() => _TestShareChildWidgetState();
}
class _TestShareChildWidgetState extends State<TestShareChildWidget> {
  @override
  void didChangeDependencies() {
    ///如build 方法中沒有使用 InheritedShareWidget 的數據，那么它的didChangeDependencies()將不會被調用
    super.didChangeDependencies();
    print("enter didChangeDependencies");
  }
  @override
  Widget build(BuildContext context) {
    print("enter child build");
    //獲取Inherited的共享數據：
    final data = InheritedShareWidget.of(context).data.toString();
    return Text(data);
  }
}

class _TestInheritedWidgetState extends State<TestInheritedWidget> {
  int count = 0;
  @override
  Widget build(BuildContext context) {
    return Center(
      child: InheritedShareWidget(
        data: count,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            TestShareChildWidget(),
            RaisedButton(
                child: Text('add'),
                onPressed: () {
                  setState(() {
                    ++count;
                  });
                })
          ],
        ),
      ),
    );
  }
}