说到InheritedWidget，想必大家也都知道这个是Flutter里面非常重要的组件，很多功能场景都是基于InheritedWidget处理实现的，如：Locale、Theme、登录信息以及provider状态管理也是基于InheritedWidget实现

下面先用个小例子，初步学习一下InheritedWidget在不同的widget中通过dependOnInheritedWidgetOfExactType获得共同的数据：

先创建个model

class CNUserModel {
  final int count;
  const CNUserModel(this.count);
}

再创建一个MyIneritedWidget:

class MyInheritedTest extends InheritedWidget {
  final CNUserModel? countModel;
  final Function()? add;

  MyInheritedTest({Key? key, this.countModel, this.add, Widget? child})
      : super(key: key, child: child!);

  //静态方法 方便调用
  // static MyInheritedTest? of(BuildContext context) {
  //   return context.dependOnInheritedWidgetOfExactType(aspect: MyInheritedTest());
  // }

  //静态方法 方便调用
  static MyInheritedTest? of(BuildContext context) {
    return context.dependOnInheritedWidgetOfExactType(aspect: MyInheritedTest);
  }

  //是否重建widget就取决于数据是否相同
  @override
  bool updateShouldNotify(covariant MyInheritedTest oldWidget) {
    // TODO: implement updateShouldNotify
    return countModel != oldWidget.countModel;
  }
}

这里代码有个地方有个问题，我当时敲的时候，没很注意，就是：context.dependOnInheritedWidgetOfExactType(aspect: MyInheritedTest())，结果就是理所当然的报错：

When the exception was thrown, this was the stack: 
#0      new MyInheritedTest (package:getx_demo/first_page.dart:133:37)
#1      MyInheritedTest.of (package:getx_demo/first_page.dart:137:17)
#2      A_View.build (package:getx_demo/first_page.dart:58:43)
#3      StatelessElement.build (package:flutter/src/widgets/framework.dart:4876:49)
#4      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4806:15)
#5      Element.rebuild (package:flutter/src/widgets/framework.dart:4529:5)
#6      BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2659:19)
#7      WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:891:21)
#8      RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:370:5)
#9      SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1146:15)
#10     SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1083:9)
#11     SchedulerBinding.scheduleWarmUpFrame.<anonymous closure> (package:flutter/src/scheduler/binding.dart:864:7)

所以，敲的时候要注意哈！！！

创建两个View使用处理和接收一下数据，看是否能共享成：

class A_View extends StatelessWidget {
  const A_View({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final inheritedTest = MyInheritedTest.of(context);
    final testModel = inheritedTest?.countModel;
    debugPrint('A_View中的值:  ${testModel?.count}');

    return Padding(
      padding: const EdgeInsets.only(left: 10.0, top: 10.0, right: 10.0),
      child: GestureDetector(
        onTap: inheritedTest?.add,
        child: Container(
            height: 40,
            width: 100,
            alignment: Alignment.center,
            decoration: BoxDecoration(
                color: Colors.blue, borderRadius: BorderRadius.circular(5)),
            child: const Text(
              'add method',
              style: TextStyle(color: Colors.white),
            )),
      ),
    );
  }
}

class B_View extends StatelessWidget {
  const B_View({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final testModel = MyInheritedTest.of(context)?.countModel;
    print('B_View中的值:  ${testModel?.count}');
    return Padding(
      padding: const EdgeInsets.only(left: 10.0, top: 10.0, right: 10.0),
      child: Text(
        '当前count:${testModel?.count}',
        style: const TextStyle(fontSize: 20.0),
      ),
    );
  }
}

使用刚刚创建的MyInheritedWidget ：

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

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

class _FirstPageState extends State<FirstPage> {
  CNUserModel? testModel;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    _initData();
  }

  _initData() {
    testModel = const CNUserModel(0);
  }

  _add() {
    setState(() {
      testModel = CNUserModel(testModel!.count + 1);
    });
  }

  @override
  Widget build(BuildContext context) {
    return MyInheritedTest(
      countModel: testModel,
      add: _add,
      child: Scaffold(
        appBar: AppBar(
          title: const Text("InheritedWidgetTestDemo"),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: const [A_View(), B_View()],
          ),
        ),
      ),
    );
  }
}

截屏2022-10-19 10.43.38.png

通过控制台日志可以看出，数据操作和共享是成功的了

简单demo到这就完成了，那么demo终究是demo，怎么实际应用到项目中去呢，接下来咱们就稍微修改修改，使用Provider二者结合实现保存和共享用户信息操作：

model修改下，要保存用户信息嘛：

class CNUserModel {
  String? name;
  int? sex;

  CNUserModel({this.name, this.sex});
}

新增一个继承ChangeNotifier的CNUserTool用来接收更新数据：

class CNUserTool extends ChangeNotifier {
  CNUserTool(this._userInfo);

  CNUserModel _userInfo;

  CNUserModel get userInfo => _userInfo;

  void update(CNUserModel userInfo) {
    _userInfo = userInfo;
    notifyListeners();
  }
}

MyInheritedTest稍作修改：

class MyInheritedTest extends InheritedWidget {
  // final CNUserModel? userModel;
  ValueNotifier<CNUserModel>? _valueNotifier;
  ValueNotifier<CNUserModel> get valueNotifier => _valueNotifier!;

  MyInheritedTest({Key? key, CNUserModel? userModel, Widget? child})
      : super(key: key, child: child!) {
    _valueNotifier = ValueNotifier<CNUserModel>(userModel!);
  }

  void updateData(CNUserModel info) {
    _valueNotifier?.value = info;
  }

  //静态方法 方便调用
  static MyInheritedTest? of(BuildContext context) {
    return context.dependOnInheritedWidgetOfExactType<MyInheritedTest>();
  }

  @override
  bool updateShouldNotify(covariant MyInheritedTest oldWidget) {
    return false;
  }
}

B_View也稍作修改：

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

  @override
  State<B_View> createState() => _B_ViewState();
}

class _B_ViewState extends State<B_View> {
  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {

    CNUserTool userTool = Provider.of<CNUserTool>(context);

    return Text('name: ${userTool.userInfo.name}\n'
        '性别: ${userTool.userInfo.sex! % 2 == 0 ? "男" : "女"}');

  }
}

使用：

    return Scaffold(
      appBar: AppBar(title: const Text('InheritedWidgetDemoPage')),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [

          B_View(),
          const SizedBox(
            height: 20,
          ),
          Consumer<CNUserTool>(
            builder: (BuildContext context, value, Widget? child) {
              return ElevatedButton(
                  onPressed: () {
                    value.update(CNUserModel(name: 'lyl', sex: _clickCount++));
                  },
                  child: const Text("修改信息"));
            },
          ),
        ],
      ),
    );

因为是全局共享用户信息嘛，所以入口函数就要处理对应操作：

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    //初始数据值，一般是读取本地存储，这里直接给默认，具体场景具体处理
    CNUserModel userModel = CNUserModel(name: "lyl", sex: 2);
    return MultiProvider(
      providers: [
        // ChangeNotifierProvider.value(value: CNUserTool(userModel)),
        ChangeNotifierProvider.value(value: CNUserTool(userModel)),
      ],
      child: GetMaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: const HomePage(),
        routes: const {},
      ),
    );
  }
}

20221019-112802.gif

通过gif可以在HomePage里面也读取了对应用户信息数据，可见是正常获取以及共享的。至此，实际应用场景也完成了。

生活百般滋味，人生需要笑对~😄