[Flutter] StatelessWidget 에서 시작 시 함수를 호출하는 방법

class Example extends StatefulWidget {

  Example ({Key key}) : super (key : key);

  _ExampleState createState () => _ExampleState ();
}

class _ExampleState extends State <Example> {

  @override
  void initState () {
    _getThingsOnStartup (). then ((value) {
      print ( 'Async done');
    });
    super.initState ();
  }

  @override
  Widget build (BuildContext context) {
  return Container ();
  }
  
  Future _getThingsOnStartup () async {
    await Future.delayed (Duration (seconds : 2));
  }
}

/// 상태 위젯에서 onInit 호출을 제공하는 상태 저장 기능 용 래퍼
class StatefulWrapper extends StatefulWidget {
  final Function onInit;
  final Widget child;

  const StatefulWrapper ({@ required this.onInit, @required this.child});
  
  @override
  _StatefulWrapperState createState () => _StatefulWrapperState ();
}

class _StatefulWrapperState extends State <StatefulWrapper> {

  @override
  void initState () {
    if (widget.onInit != null) {
      widget.onInit ();
    }
    super.initState ();
  }

  @override
  Widget build (BuildContext context) {
    return widget.child;
  }
}

class StartupCaller extends StatelessWidget {
  
  @override
  Widget build (BuildContext context) {
    return StatefulWrapper (
      onInit : () {
        _getThingsOnStartup (). then ((value) {
          print ( 'Async done');
        });
      },
      child : Container () ,
    );
  }
  
  Future _getThingsOnStartup () async {
    await Future.delayed (Duration (seconds : 2));
  }
}

출처 - https://medium.com/filledstacks/how-to-call-a-function-on-start-in-flutter-stateless-widgets-28d90ab3bf49