Flutter extract async to separator class and methods - asynchronous

Question

My implementation repository
in main method i have this lines of code to connect to database and work fine
Future<void> main() async {
final database = await $FloorAppDatabase.databaseBuilder('flutter_database.db').build();
final userDao = database.userDao;
runApp(MaterialApp(...);
}
now i'm trying to use this codes
final database = await $FloorAppDatabase.databaseBuilder('flutter_database.db').build();
final userDao = database.userDao;
from class, for example:
Future<void> main() async {
MyDatabase myDatabase = MyDatabase();
final userDao = myDatabase.userDao;
runApp(MaterialApp(...);
}
unfortunately i get null for userDao in this implementation, i think in that witch i use async i should be change that and use then()
class MyDatabase {
UserDao userDao;
Future<UserDao> initialDatabase() async {
final database = await $FloorAppDatabase.databaseBuilder('flutter_database.db').build();
return database.userDao;
}
}
#dao
abstract class UserDao{
#Query('SELECT * FROM User LIMIT 1')
Stream<User> getUserInfo();
#insert
Future<void> insertUserInformation(User user);
}
UPDATED: implementation solution on scope model
class MydbModel extends Model {
MyDatabase myDatabase = MyDatabase();
Future _doneFuture;
MydbModel() {
_doneFuture= myDatabase.initialDatabase();
}
Future get initializationDone => _doneFuture;
}
class MyDatabase {
AppDatabase db;
UserDao userDao;
Future<void> initialDatabase() async {
db = await $FloorAppDatabase.databaseBuilder('flutter_database.db').build();
}
UserDao getUserDao() {
return db.userDao;
}
}
main() {
runApp(MaterialApp(
title: 'floor sample',
home: App(),
));
}
class App extends StatefulWidget {
App({Key key}) : super(key: key);
#override
State<App> createState() => _AppState();
}
class _AppState extends State<App> {
#override
Widget build(BuildContext context) {
return Scaffold(
body: ScopedModel(
model: MydbModel(),
child: ScopedModelDescendant<MydbModel>(
builder: (context, _, model) => StreamBuilder<User>(
stream: model.myDatabase.userDao.getUserInfo(),
builder: (_, snapshot) {
if (!snapshot.hasData) {
return Text('user not found');
} else {
return Text('user found');
}
},
),
),
),
);
}
}

Answer 1

With given class implementation, you should call the function and wait until it completes:
MyDatabase myDatabase = MyDatabase();
final userDao = await myDatabase.initialDatabase();
Alternatively, if you don't want to recreate databse instance each time, consider assigning it to a class member
class MyDatabase {
AppDatabase db;
Future<void> initDb() async {
db = await $FloorAppDatabase.databaseBuilder('flutter_database.db').build();
}
UserDao getUserDao() {
return db.userDao;
}
// here may be other functions that use db
}
And the use it like this
MyDatabase myDatabase = MyDatabase();
await myDatabase.initDb();
final userDao = myDatabase.getUserDao();
// here you can call other functions from class