I have problem with async-await. (I am not very good at programming, but learning by creating random apps...)

Problem: Using dio to get data from Node.js json-server, but I cant transform data from

Future to List. Error: type 'Future' is not a subtype of type 'List' at line 13. List<Routes> routes = _getData();

I have read a lot of discussions here on stackoverflow and many other websites, but I just can't make it work. :( So here I am asking with specific code.

Needed code:

1. Code where error appears (route_list_screen.dart)

import 'package:falcoo/api/api.dart';
import 'package:flutter/material.dart';
import 'package:falcoo/models/routes.dart';

class RouteList extends StatefulWidget {
  const RouteList({Key? key}) : super(key: key);

  @override
  State<RouteList> createState() => _RouteListState();
}

List<Routes> routes = _getData();

class _RouteListState extends State<RouteList> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Výber trasy'),
        automaticallyImplyLeading: true,
        centerTitle: true,
      ),
      body: ListView.separated(
        itemCount: routes.length,
        itemBuilder: (context, index) {
          return ListTile(
            title: Text(routes[index].number),
            subtitle: Text(routes[index].routeType),
            trailing: const Text('??/??'),
            onTap: () {
              Navigator.push(
                context,
                MaterialPageRoute(
                  builder: (context) => RouteSelected(
                    passedRoutes: routes[index],
                  ),
                ),
              );
            },
          );
        },
        separatorBuilder: (context, index) {
          return const Divider();
        },
      ),
    );
  }
}

_getData() async {
  Future<dynamic> futureOfRoutes = getRouteList(856);
  List<dynamic> routes = await futureOfRoutes;
  return routes;
}

2. Connecting to server (api.dart)

import 'package:falcoo/models/routes.dart';

const _url = 'http://10.0.2.2:3000/routes';

getRouteList(int driverId) async {
  Response response;
  var dio = Dio(BaseOptions(
    responseType: ResponseType.plain,
  ));
  response = await dio.get(_url, queryParameters: {"driver_id": driverId});
  final data = routesFromJson(response.data);
  return data;
}

List with param Routes = Routes is model from app.quicktype.io

CodePudding user response：

_getData() returns a future, you can't direct assign it on List<Routes> where it is Future<dynamic>.

You can use initState

class _RouteListState extends State<RouteList> {
  List<Routes>? routes;

  _loadData() async {
    routes = await _getData();
    setState(() {});
  }

  @override
  void initState() {
    super.initState();
    _loadData();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: routes == null
          ? Text("On Future ....")
          : ListView.separated(
              itemCount: routes?.length??0,
              itemBuilder: (context, index) {
                return ListTile(
                  title: Text(routes![index].number),
                  subtitle: Text(routes![index].routeType),
                  trailing: const Text('??/??'),
                  onTap: () {
                    Navigator.push(
                      context,
                      MaterialPageRoute(
                        builder: (context) => RouteSelected(
                          passedRoutes: routes![index],
                        ),
                      ),
                    );
                  },
                );
              },
              separatorBuilder: (context, index) {
                return const Divider();
              },
            ),
    );
  }
}

Also check FutureBuilder