Fetch state-object from database - flutter

Question

I want to get my state from database upon startup. I use provider with ChangeNotivierProvider at my first widget. Code included for clarification.
This is my main method, it has the widget that provides the state i plan to use in the app:
void main() => runApp(
ChangeNotifierProvider(
child: MyApp(),
builder: (context) => StateDao.get(),
),
}
My DAO just returns the state from database (i use sembast, but could just as easily be sqflite or Firebase)
Future<State> get() async {
// Database logic
}
State is just an object extending ChangeNotifier
class State extends ChangeNotifier {
// Getters, setters, changeNotifiers etc.
}
This will not work as i cannot call async methods in the builder-method of ChangeNotifierProvider. How, when and where should this be initialized? As i understand it, async calls should not be done in any build methods. I tried overriding didChangeDependencies that provided context-access but i could not get past the async-call in builder method limitation.

Answer 1

You can initialize the value in initState. For example, you can store Future object and use FutureBuilder to build widget when a value is resolved:
Future<State> futureState;
#override
void initState() {
// Calling async method and storing Future object
futureState = StateDao.get();
super.initState();
}
#override
Widget build(BuildContext context) {
return FutureBuilder<State>(
future: futureState,
builder: (context, snapshot) {
// No data yet, showing loader
if (!snapshot.hasData) {
return CircularProgressIndicator();
}
return ChangeNotifierProvider(
child: MyApp(),
builder: (context) => snapshot.data,
);
},
);
}
Another similar approach is to use StreamController and StreamBuilder:
final StreamController<State> stateStream = StreamController<State>();
#override
void initState() {
// Calling async method and setting callback to add data to the stream
StateDao.get().then((v) => stateStream.add(v));
super.initState();
}
#override
void dispose() {
// Closing the sink
stateStream.close();
super.dispose();
}
#override
Widget build(BuildContext context) {
return StreamBuilder<State>(
stream: stateStream.stream,
builder: (context, snapshot) {
// No data yet, showing loader
if (!snapshot.hasData) {
return CircularProgressIndicator();
}
return ChangeNotifierProvider(
child: MyApp(),
builder: (context) => snapshot.data,
);
},
);
}
If you need more complex architecture, you might want to look at BLoC, which is very popular architecture in Flutter community.