DART

perform async task when build is done flutter

@override
Widget build(BuildContext context) {
  executeAfterBuild();
  return Container();
}

Future<void> executeAfterBuild() async {
  // this code will get executed after the build method
  // because of the way async functions are scheduled
}

flutter build async

class MyWidget extends StatelessWidget {
  @override
  Widget build(context) {
    return FutureBuilder<String>(
      future: callAsyncFetch(),
      builder: (context, AsyncSnapshot<String> snapshot) {
        if (snapshot.hasData) {
          return Text(snapshot.data);
        } else {
          return CircularProgressIndicator();
        }
      }
    );
  }
}