我很初学者..刚刚开始学习颤振。我关注 Google Codelabs 中的“Your First Flutter App”,并停在这一步:https://codelabs.developers.google.com/codelabs/flutter-codelab-first?hl=en#6
该指令要分为 2 列,用户可以在收藏夹页面看到他们选择的收藏夹名称。 我将代码复制到我的 main.dart (我使用 Visual Studio Code),保存文件后,我在视图中没有看到任何更改...我重新调试应用程序,Visual Studio 代码说:
您的项目中存在构建错误。
问题是: 没有为类型“MyAppState”定义吸气剂“favorites”。 尝试导入定义“favorites”的库,将名称更正为现有 getter 的名称,或者定义名为“favorites”的 getter 或字段。
任何人都可以帮我解决这个案子吗...非常感谢
我尝试从 https://codelabs.developers.google.com/codelabs/flutter-codelab-first?hl=en#6
复制代码我复制后的所有 main.dart 如下:
import 'package:english_words/english_words.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
Widget build(BuildContext context) {
return ChangeNotifierProvider(
create: (context) => MyAppState(),
child: MaterialApp(
title: 'my_awesome_namer',
theme: ThemeData(
useMaterial3: true,
colorScheme: ColorScheme.fromSeed(seedColor: Color.fromRGBO(90, 124, 181, 1)),
),
home: MyHomePage(),
),
);
}
}
class MyAppState extends ChangeNotifier {
var current = WordPair.random();
// ↓ Add this.
void getNext() {
current = WordPair.random();
notifyListeners();
}
void toggleFavorite() {}
}
// ...
// ...
class MyHomePage extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
body: Row(
children: [
SafeArea(
child: NavigationRail(
extended: false,
destinations: [
NavigationRailDestination(
icon: Icon(Icons.home),
label: Text('Home'),
),
NavigationRailDestination(
icon: Icon(Icons.favorite),
label: Text('Favorites'),
),
],
selectedIndex: 0,
onDestinationSelected: (value) {
print('selected: $value');
},
),
),
Expanded(
child: Container(
color: Theme.of(context).colorScheme.primaryContainer,
child: GeneratorPage(),
),
),
],
),
);
}
}
class GeneratorPage extends StatelessWidget {
@override
Widget build(BuildContext context) {
var appState = context.watch<MyAppState>();
var pair = appState.current;
IconData icon;
if (appState.favorites.contains(pair)) {
icon = Icons.favorite;
} else {
icon = Icons.favorite_border;
}
return Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
BigCard(pair: pair),
SizedBox(height: 10),
Row(
mainAxisSize: MainAxisSize.min,
children: [
ElevatedButton.icon(
onPressed: () {
appState.toggleFavorite();
},
icon: Icon(icon),
label: Text('Like'),
),
SizedBox(width: 10),
ElevatedButton(
onPressed: () {
appState.getNext();
},
child: Text('Next'),
),
],
),
],
),
);
}
}
// ...
class BigCard extends StatelessWidget {
const BigCard({
super.key,
required this.pair,
});
final WordPair pair;
@override
Widget build(BuildContext context) {
final theme = Theme.of(context); // ← Add this.
// ↓ Add this.
final style = theme.textTheme.displayMedium!.copyWith(
color: theme.colorScheme.onPrimary,
);
return Card(
color: theme.colorScheme.primary, // ← And also this.
child: Padding(
padding: const EdgeInsets.all(20),
// ↓ Change this line.
// ↓ Make the following change.
child: Text(
pair.asLowerCase,
style: style,
semanticsLabel: "${pair.first} ${pair.second}",
),
),
);
}
}
// ...
我期望: 主页分为 2 列,用户可以在收藏夹页面看到他们选择的收藏夹名称(稍后将添加来自谷歌代码实验室的额外代码)
您需要在 favorites
MyAppState
的列表。将会是
class MyAppState extends ChangeNotifier {
var current = WordPair.random();
// ↓ Add this.
void getNext() {
current = WordPair.random();
notifyListeners();
}
var favorites = <WordPair>[]; //this line
void toggleFavorite() {}
}