import 'package:flutter/material.dart';

void main() {
  runApp(const MaterialApp(
    home: ValueListenableWidget(),
  ));
}

//InheritedWidget 提供从上到下共享数据
class ShareDataWidget extends InheritedWidget {
  const ShareDataWidget({
    Key? key,
    required this.data,
    required Widget child,
  }) : super(key: key, child: child);

  //子树中的共享数据
  final int data;

  //方便子树获取共享数据
  static ShareDataWidget? of(BuildContext context) {
    return context.dependOnInheritedWidgetOfExactType<ShareDataWidget>();
  }

  //data变化是否通知子组件中依赖的data重新build
  @override
  bool updateShouldNotify(ShareDataWidget old) {
    return old.data != data;
  }
}

class TestWidget extends StatefulWidget {
  const TestWidget({Key? key}) : super(key: key);

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

class _TestWidgetState extends State<TestWidget> {
  @override
  Widget build(BuildContext context) {
    //使用InheritedWidget中的共享数据
    return Text(ShareDataWidget.of(context)!.data.toString());
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    //如果build中没有依赖InheritedWidget，则此回调不会调用。
    print("Dependencies change");
  }
}

class InheritedWidgetTest extends StatefulWidget {
  const InheritedWidgetTest({Key? key}) : super(key: key);

  @override
  State createState() => _InheritedWidgetTestState();
}

class _InheritedWidgetTestState extends State<InheritedWidgetTest> {
  int count = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ShareDataWidget(
        data: count,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const Padding(
              padding: EdgeInsets.only(bottom: 20.0),
              child: TestWidget(),
            ),
            ElevatedButton(
              child: const Text("Increment"),
              //重新build，ShareDataWidget的data更新
              onPressed: () => setState(() => ++count),
            )
          ],
        ),
      ),
    );
  }
}

//局部builder
class ValueListenableWidget extends StatefulWidget {
  const ValueListenableWidget({Key? key}) : super(key: key);

  @override
  State createState() => _ValueListenableState();
}

class _ValueListenableState extends State<ValueListenableWidget> {
  static const double textScaleFactor = 1.5;

  //数字变化通知 ValueListenableBuilder
  final ValueNotifier<int> _counter = ValueNotifier(0);

  @override
  Widget build(BuildContext context) {
    //+ 按钮不会触发组件 build
    print('build');
    return Scaffold(
      appBar: AppBar(title: const Text('ValueListenableBuilder 测试')),
      body: Center(
        child: ValueListenableBuilder<int>(
          builder: (BuildContext context, int value, Widget? child) {
            print('_counter change build');
            return Row(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                child!,
                Text('$value 次', textScaleFactor: textScaleFactor),
              ],
            );
          },
          valueListenable: _counter,
          child: const Text('点击了 ', textScaleFactor: textScaleFactor),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        child: const Icon(Icons.add),
        onPressed: () => _counter.value += 1,
      ),
    );
  }
}