LateStatic.dart

void main() async {
  runApp(const MyApp());

  // 初期化後
  await LateStaticUtil.initialize();

  // 初期化前に呼ぶ、初期化されていたら1になってる
  var num = await LateStatic().getNumber();
  print(num);

}

class LateStaticUtil {
  static Future initialize() async {
    print('初期化し始める');
    await LateStatic.initialize();
  }
}

class LateStatic {
  static bool isInitialized = false;
  static int number = 0;

  static Future initialize() async {
    print('初期化がはじまり');
    await Future.delayed(Duration(seconds: 5));
    number++;
    isInitialized = true;
    print('初期化が終わり');
  }

  Future<int> getNumber() async {
    await Future.doWhile(() => !isInitialized);
    print('初期化が終わったのでnumberを返せる');
    return number;
  }
}

/*
Running Gradle task 'assembleDebug'...
✓  Built build/app/outputs/flutter-apk/app-debug.apk.
Installing build/app/outputs/flutter-apk/app.apk...
Debug service listening on ws://127.0.0.1:59977/M224qsv5dF0=/ws
Syncing files to device sdk gphone64 arm64...
I/flutter (28415): 初期化し始める
I/flutter (28415): 初期化がはじまり
E/SurfaceSyncer(28415): Failed to find sync for id=0
W/Parcel  (28415): Expecting binder but got null!
I/flutter (28415): 初期化が終わり
I/flutter (28415): 初期化が終わったのでnumberを返せる
I/flutter (28415): 1
*/