如何使用提供程序在Flutter中添加依赖项注入

Question

void main() => runApp(MultiProvider(providers: [
ChangeNotifierProvider(
create: (BuildContext context) => QuoteViewModel(),
),
ChangeNotifierProvider(
create: (BuildContext context) => AuthorViewModel(),
),
], child: MyApp()));
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Poems',
home: PoemsListPage(),
);
}
}

main.dart

class QuoteListPage extends StatefulWidget {
@override
_QuoteListPageState createState() => _QuoteListPageState();
}
class _QuoteListPageState extends State<QuoteListPage> {
@override
Widget build(BuildContext context) {
final model = Provider.of<QuoteViewModel>(context);
return Scaffold(
appBar: AppBar(title: Text('Poems List')),
body: _buildBody(model.getQuotes()),
);
}
Widget _buildBody(List<Quote> quotes) => ListView(
children: quotes
.map((quote) => ListTile(
title: Text(quote.body),
))
.toList(),
);
}

quoteListPage.dart

class Quote {
final String id;
final String authorId;
final String body;
Quote(this.id, this.authorId, this.body);
}
class Author {
final String id;
final String name;
Author(this.id, this.name);
}

型号.省道

class Repository {
final Api _api = Api();
final Database _database = Api();
List<Quote> getQuotes() => [];
List<Author> getAuthors() => [];
}

repository.dart

class QuoteViewModel with ChangeNotifier {
final Repository _repository = Repository();
List<Quote> getQuotes() => _repository.getQuotes();
}
class AuthorViewModel with ChangeNotifier {
final Repository _repository = Repository();
List<Author> getAuthors() => _repository.getAuthors();
}

notifiers.dart

在阅读Medium上的一篇文章后，我曾尝试使用ProxyProvider，但最终出现错误"这可能是一个错误，因为提供程序不会自动更新从属项">

List<SingleChildWidget> globalProviders = [
Provider.value(value: Api()),
Provider.value(value: Database()),
ProxyProvider2<Api, Database, Repository>(
update: (_, api, database, __) => Repository(api, database),
),
ProxyProvider<Repository, QuoteViewModel>(
update: (_, repo, __) => QuoteViewModel(repo),
),
ProxyProvider<Repository, AuthorViewModel>(
update: (_, repo, __) => AuthorViewModel(repo),
)
];
void main() => runApp(
MultiProvider(
providers: globalProviders,
child: MyApp(),
),
);

main.dart(更新(

class Repository {
final Api _api;
final Database _database;
Repository({@required api, @required database})
: _api = api,
_database = database;
List<Quote> getQuotes() => [];
List<Author> getAuthors() => [];
}

repository.dart(更新版(

class QuoteViewModel with ChangeNotifier {
final Repository _repository;
QuoteViewModel({@required repository}) : _repository = repository;
List<Quote> getQuotes() => _repository.getQuotes();
}
class AuthorViewModel with ChangeNotifier {
final Repository _repository;
AuthorViewModel({@required repository}) : _repository = repository;
List<Author> getAuthors() => _repository.getAuthors();
}

notifiers.dart(更新版(

Answer 1

Flutter有一个使用提供程序包的指南，可以帮助您。https://flutter.dev/docs/development/data-and-backend/state-mgmt/simple如果您能更具体地处理您与提供商之间的问题，这将非常有帮助。