Dart Riverpod：未定义 class 'WidgetRef'

Question

我正在浏览 Flutter Riverpod 包文档，出于某种原因 'Getting started' 中的基本 example 抛出错误：

Undefined class 'WidgetRef'. Try changing the name to the name of an existing class, or creating a class with the name 'WidgetRef'.

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

final helloWorldProvider = Provider((_) => 'Hello World');

void main() {
  runApp(
    ProviderScope(child: MyApp()),
  );
}

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

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final String value = ref.watch(helloWorldProvider);
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: Text(value),
        ),
      ),
    );
  }
}

pubspec.yaml

environment:
  sdk: ">=2.12.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter

  cupertino_icons: ^1.0.2
  flutter_riverpod: ^0.14.0+3

dev_dependencies:
  flutter_test:
    sdk: flutter

Answer 1

在您的 pubspec 中您指定了 flutter_riverpod: ^0.14.0+3，而 WidgetRef 仅适用于版本 1.0.0（目前是开发版本而非完整版本）。

在您的 Riverpod 版本中，您可以按如下方式使用 ConsumerWidget：

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

  @override
  Widget build(BuildContext context, ScopedReader watch) {
    final String value = watch(helloWorldProvider);
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: Text(value),
        ),
      ),
    );
  }
}

或者，您可以升级到 flutter_riverpod: ^1.0.0-dev.6

Dart Riverpod：未定义 class 'WidgetRef'

Dart Riverpod: Undefined class 'WidgetRef'

dart

flutter

riverpod