Error: Could not find the correct ScopedModel when using ScopedModel.of<MyModel>(context)

Question

作为研究 flutter 状态管理的局外人，我喜欢使用 scoped_model 进行状态管理的想法，正如 flutter.dev 中所推荐的那样。我重写了计数器应用运行。我可以使用 ScopedModelDescendant<CounterModel> 访问模型属性，但使用 ScopedModel.of<CounterModel>(context) 访问模型属性时遇到问题。有人可以建议我可能做错了什么吗？我有一种预感，它可能是 ScopedModel 在我的小部件树中的位置。我的代码和错误消息如下。

main.dart

import 'package:flutter/material.dart';
import 'package:scoped_model/scoped_model.dart';
import 'package:second/model/counter_model.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  Widget build(context) {
    return ScopedModel(
      model: new CounterModel(),
      child: Scaffold(
          appBar: AppBar(
            title: Text('ScopedModel'),
          ),
          body: ScopedModelDescendant<CounterModel>(
            builder: (context, child, value) {
              return Text("Pressed ${value.counter} times");
            },
          ),
          floatingActionButton: buildFab1()),
    );
  }

  Widget buildFab1() {
    return ScopedModelDescendant<CounterModel>(
      builder: (context, child, model) => FloatingActionButton(
            child: Icon(Icons.add),
            onPressed: model.incrementCounter,
          ),
    );
  }

  Widget buildFab2(BuildContext context) {
    return FloatingActionButton(
      child: Icon(Icons.add),
      onPressed: ScopedModel.of<CounterModel>(context).incrementCounter,
    );
  }
}

model/counter_model.dart

import 'package:scoped_model/scoped_model.dart';

class CounterModel extends Model {
  int _counter = 0;

  int get counter => _counter;

  void incrementCounter() {
    _counter++;
    notifyListeners();
  }
}

在main.dart中，如果我使用buildFab2(context)而不是buildFab1()，我会得到以下错误


flutter: The following ScopedModelError was thrown building ScopedModelDescendant<Model>(dirty):
flutter: Error: Could not find the correct ScopedModel.
flutter:
flutter: To fix, please:
flutter:
flutter:   * Provide types to ScopedModel<MyModel>
flutter:   * Provide types to ScopedModelDescendant<MyModel>
flutter:   * Provide types to ScopedModel.of<MyModel>()
flutter:   * Always use package imports. Ex: `import 'package:my_app/my_model.dart';
flutter:

我看了一些 SO 问题，但 none 有所帮助。

Answer 1

是的，那是因为，您通过的 context 不会有 CounterModel 的 ScopedModel。

你可以做的是将你的 buildFab2 包裹在一个 Builder 小部件中，这将为你提供一个 context 具有 ScopedModel 和 CounterModel 作为父级.

喜欢：

Builder(
    builder: (context){
      return buildFab2(context);
    },
  )

您的应用将如下所示：

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  Widget build(context) {
    return ScopedModel(
      model: new CounterModel(),
      child: Scaffold(
        appBar: AppBar(
          title: Text('ScopedModel'),
        ),
        body: ScopedModelDescendant<CounterModel>(
          builder: (context, child, value) {
            return Text("Pressed ${value.counter} times");
          },
        ),
        floatingActionButton: Builder(
          builder: (context) {
            // return buildFab1() if fab one required
            return buildFab2(context);
          },
        ),
      ),
    );
  }

  Widget buildFab1() {
    return ScopedModelDescendant<CounterModel>(
      builder: (context, child, model) => FloatingActionButton(
            child: Icon(Icons.add),
            onPressed: model.incrementCounter,
          ),
    );
  }

  Widget buildFab2(BuildContext context) {
    return FloatingActionButton(
      child: Icon(Icons.add),
      onPressed: ScopedModel.of<CounterModel>(context).incrementCounter,
    );
  }
}

希望对您有所帮助！

Answer 2

您需要像这样在 main.dart 中添加 scoppedmodel：

@override
  Widget build(BuildContext context){
    return ScopedModel<UserModel>(
        model: UserModel(),
        child: MaterialApp(
            title: "Quiz Flamengo",
            debugShowCheckedModeBanner: false,
            home: Scaffold(
              body: HomeScreen(),
            )
        )
    );
  }

Error: Could not find the correct ScopedModel when using ScopedModel.of<MyModel>(context)

Error: Could not find the correct ScopedModel when using ScopedModel.of<MyModel>(context)

dart

flutter

scoped-model