Flutter Futures: How can I make this StompClient connection awaitable with Futures? - flutter

Question

I am using StompClient to connect to my gameservers websocket endpoint. For the sake of using FutureBuilder of Flutter I'd like to have async/await features with this client.
Therefore I wrapped the StompClient in the following way:
class CombatClient {
late StompClient _client;
Future<bool> connect() async {
_client = StompClient(
config: StompConfig.SockJS(
url: '${ServerGlobals.backendHost}/connect',
onConnect: (frame) async {
_client.subscribe(destination: "/gameserver/foo", callback: (data) => {print("foo: ${data.body}")});
},
),
);
_client.activate();
return await Future.doWhile(() => _client.connected);
}
}
In my main logic I am using the whole like this:
final combatClient = CombatClient();
await combatClient.connect();
However this does not work because of the following error:
E/flutter (23147): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: type 'Null' is not a subtype of type 'FutureOr<bool>'
E/flutter (23147): #0 CombatClient.connect (package:app/combat/websocket/combat_client.dart:19:12)
E/flutter (23147): <asynchronous suspension>
E/flutter (23147): #1 _DebugCombatPageState.build.<anonymous closure> (package:app/debug/debug_combat_page.dart:61:27)
E/flutter (23147): <asynchronous suspension>
E/flutter (23147):
Regardless of the error I'd just love to know what the proper approach is. I always struggle when it comes to Futures etc. I can't find the right API usage to make my connection to the game server awaitable.

Answer 1

Quoted from #pskink
simply use Completer class instead of return await Future.doWhile(... - the docs say: "A way to produce Future objects and to complete them later with a value or error"