info_tren/lib/train_info_page/train_info.dart

import 'dart:io' show Platform;

import 'package:flutter/material.dart';
import 'package:flutter/cupertino.dart';

import 'package:info_tren/models/train_data.dart';
import 'package:info_tren/train_info_page/train_info_cupertino.dart';
import 'package:info_tren/train_info_page/train_info_material.dart';

mixin TrainInfoMixin {
  String title;
  bool showTrainData;
  TrainLookupResult lookupResult;
  bool requestedData;
}

class TrainInfo extends StatelessWidget {
  final int trainNumber;

  TrainInfo({@required this.trainNumber});

  @override
  Widget build(BuildContext context) {
    return TrainDataWebViewAdapter(
      builder: (context) {
        if (Platform.isAndroid) {
          return TrainInfoMaterial(trainNumber: trainNumber,);
        }
        else if (Platform.isIOS) {
          return TrainInfoCupertino(trainNumber: trainNumber,);
        }

        return null;
      },
    );
  }
}

typedef FutureDisplayCallback<T>(BuildContext context, T data);

class FutureDisplay<T> extends StatelessWidget {
  final Future<T> future;
  final FutureDisplayCallback<T> builder;

  FutureDisplay({Key key, @required this.future, @required this.builder}): super(key: key);

  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      future: future,
      builder: (context, snapshot) {
        if (snapshot.hasData) return builder(context, snapshot.data);
        if (snapshot.hasError) throw snapshot.error;
        if (snapshot.connectionState == ConnectionState.done) return Container();

        Widget loadingWidget;
        if (Platform.isAndroid) {
          loadingWidget = CircularProgressIndicator();
        }
        else if (Platform.isIOS) {
          loadingWidget = CupertinoActivityIndicator();
        }

        return Center(
          child: loadingWidget,
        );
      },
    );
  }
}