0

作为一个研究 Flutter 状态管理的局外人，我喜欢flutter.devscoped_model中推荐的使用状态管理的想法。我正在重写正在运行的计数器应用程序。我可以使用 访问模型属性，但使用 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，它可能在我的小部件树中。我的代码和错误消息如下。ScopedModelDescendant<CounterModel>ScopedModel.of<CounterModel>(context)ScopedModel

主要.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中，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:

我看了一些 SO 问题，但没有任何帮助。

4

2 回答 2

5

是的，那是因为，context你的 pass 不会有ScopedModelof CounterModel。

您可以做的是将您的小部件包装buildFab2在一个Builder小部件中，该小部件将为您提供作为父母context的东西。ScopedModelCounterModel

像：

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,
    );
  }
}

希望有帮助！

于 2019-04-26T09:37:08.277 回答
1

您需要在 main.dart 中添加 scoppedmodel，如下所示：

@override
  Widget build(BuildContext context){
    return ScopedModel<UserModel>(
        model: UserModel(),
        child: MaterialApp(
            title: "Quiz Flamengo",
            debugShowCheckedModeBanner: false,
            home: Scaffold(
              body: HomeScreen(),
            )
        )
    );
  }
于 2021-01-04T17:53:56.557 回答