错误：使用ScopedModel.of时找不到正确的ScopedModel （上下文）

Question

作为一个寻求颤动状态管理的局外人，我喜欢在scoped_model中推荐使用flutter.dev进行状态管理的想法。我重写了运行的计数器应用程序。我可以使用ScopedModelDescendant<CounterModel>访问模型属性，但是我在使用ScopedModel.of<CounterModel>(context)访问模型属性时遇到了麻烦。有人可以建议我可能做错了吗？我有一种预感，它可能是我的小部件树中的ScopedModel。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,
    );
  }
}

模型/ 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，如果我使用buildFab2(context)而不是buildFab1()，我会收到以下错误

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:

我看了几个SO问题，但都没有帮助。

Answer 1

是的，因为，你通过的context将没有ScopedModel的CounterModel。

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

喜欢：

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

你的应用程序将如下所示：

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,
    );
  }
}

希望有所帮助！