【发布时间】：2022-01-17 23:04:18
【问题描述】：
我基本上可以按照本教程了解如何在 Flutter 中实现 API：https://docs.flutter.dev/cookbook/networking/fetch-data。我按照教程进行操作，但收到一条错误消息“类型'null 不是'String' 的子类型”。我已经尝试向标头添加其他参数，但这并没有解决问题。 我使用的 API 是汽车登记处，您可以在其中输入车牌并获取车辆的所有详细信息。
final response = await http
.get(Uri.parse('https://v1.motorapi.dk/vehicles/CZ33849'),
headers: {"X-AUTH-TOKEN": "rfrzsucnc7eo3m5hcmq6ljdzda1lz793",
"Content-Type": "application/json",
"Accept": "application/json",
});
if (response.statusCode == 200) {
// If the server did return a 200 OK response,
// then parse the JSON.
return Album.fromJson(jsonDecode(response.body));
} else {
// If the server did not return a 200 OK response,
// then throw an exception.
throw Exception('Failed to load album');
}
}
//headers: {"X-AUTH-TOKEN": "rfrzsucnc7eo3m5hcmq6ljdzda1lz793"}
class Album {
final String registration_number;
final String status;
final String type;
final String use;
final String first_registration;
final String vin;
final int doors;
final String make;
final String model;
final String variant;
final String model_type;
final String color;
final String chasis_type;
final String engine_power;
final String fuel_type;
final String RegistreringssynToldsyn;
final String date;
final String result;
Album({
required this.registration_number,
required this.status,
required this.type,
required this.use,
required this.first_registration,
required this.vin,
required this.doors,
required this.make,
required this.model,
required this.variant,
required this.model_type,
required this.color,
required this.chasis_type,
required this.engine_power,
required this.fuel_type,
required this.RegistreringssynToldsyn,
required this.date,
required this.result,
});
factory Album.fromJson(Map<String, dynamic> json) {
return Album(
registration_number: json['registration_number'],
status: json['status'],
type: json['type'],
use: json['use'],
first_registration: json['first_registration'],
vin: json['vin'],
doors: json['doors'],
make: json['make'],
model: json['model'],
variant: json['variant'],
model_type: json['model_type'],
color: json['color'],
chasis_type: json['chasis_type'],
engine_power: json['engine_power'],
fuel_type: json['fuel_type'],
RegistreringssynToldsyn: json['RegistreringssynToldsyn'],
date: json['date'],
result: json['result'],
);
}
}
void main() => runApp(const MyApp());
class MyApp extends StatefulWidget {
const MyApp({Key? key}) : super(key: key);
@override
_MyAppState createState() => _MyAppState();
}
class _MyAppState extends State<MyApp> {
late Future<Album> futureAlbum;
@override
void initState() {
super.initState();
futureAlbum = fetchAlbum();
}
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Fetch Data Example',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: Scaffold(
appBar: AppBar(
title: const Text('Fetch Data Example'),
),
body: Center(
child: FutureBuilder<Album>(
future: futureAlbum,
builder: (context, snapshot) {
if (snapshot.hasData) {
return Text(snapshot.data!.registration_number);
} else if (snapshot.hasError) {
return Text('${snapshot.error}');
}
// By default, show a loading spinner.
return const CircularProgressIndicator();
},
),
),
),
);
}
}
以及来自 API 的 Json 响应（我在 python 中测试了 API）：
{'registration_number': 'CZ33849', 'status': 'Registreret', 'status_date': '2021-03-18T10:53:23.000+01:00', 'type': 'Personbil', 'use': 'Privat personkørsel', 'first_registration': '2020-03-17+01:00', 'vin': 'WVWZZZAWZLY087322', 'own_weight': None, 'total_weight': 1650, 'axels': 2, 'pulling_axels': 1, 'seats': 5, 'coupling': False, 'trailer_maxweight_nobrakes': 590, 'trailer_maxweight_withbrakes': 1000, 'doors': 4, 'make': 'VOLKSWAGEN', 'model': 'POLO', 'variant': '1,0', 'model_type': 'AW', 'model_year': 0, 'color': None, 'chassis_type': 'Hatchback', 'engine_cylinders': 3, 'engine_volume': 999, 'engine_power': 70, 'fuel_type': 'Benzin', 'registration_zipcode': '', 'vehicle_id': 9000000003974700, 'mot_info': {'type': 'RegistreringssynToldsyn', 'date': '2021-03-16', 'result': 'Godkendt', 'status': 'Aktiv', 'status_date': '2021-03-16'}}
【问题讨论】：
-
我认为编译时会产生这个错误---{'color': None , 'own_weight': None } ---in your json.