我在解析JSON时遇到问题，想要一些帮助。
这是我的JSON的摘要
"geocoded_waypoints":[ ],
"routes":[
{
"bounds":{ },
"copyrights":"Map data ©2019 Google",
"legs":[
{
"arrival_time":{ },
"departure_time":{ },
"distance":{ },
"duration":{ },
"end_address":"dsfsfsdf32434324",
"end_location":{ },
"start_address":"123123123123adsfdsfsdfsd",
"start_location":{ },
"steps":[
{
"distance":{ },
"duration":{ },
"end_location":{ },
"html_instructions":"Walk to abc",
"polyline":{ },
"start_location":{
"lat":1232131,
"lng":11231
},
"steps":[
{
"distance":{
"text":"55 m",
"value":55
},
"duration":{
"text":"1 min",
"value":52
},
"end_location":{
"lat":1.3775668,
"lng":103.8481395
},
"html_instructions":"Head \u003cb\u003ewest\u003c/b\u003e toward \u003cb\u003e123 abc Kio Ave G\u003c/b\u003e",
"polyline":{
"points":"galGu|yxRH|@BZ"
},
"start_location":{
"lat":122,
"lng":1231
},
"travel_mode":"WALKING"
},
这是我当前的代码解析JSON对象的方式
class Steps {
final String routes;
final String legs;
final String steps;
final Route html_instructions;
Steps({this.routes, this.legs, this.steps, this.html_instructions});
factory Steps.fromJson(Map<String, dynamic> json) {
return Steps(
routes: json['routes'],
legs: json['legs'],
steps: json['steps'],
html_instructions: Route.fromJson(json['html_instructions'])
);
}
static List<String> parseRoute(routesJson){
List<String> routeList = new List<String>.from(routesJson);
return routeList;
}
}
class Instructions {
final String route;
Instructions({this.route});
factory Instructions.fromJson(Map<String, dynamic> json) {
return Instructions(route: json['html_instructions']);
}
}
class Route {
final String stepp;
final Instructions instructions;
Route({this.stepp, this.instructions});
factory Route.fromJson(Map<String, dynamic> json) {
return Route(
stepp: json['html_instructions'] as String,
instructions: Instructions.fromJson(json['steps'])
);
}
}
我想要实现的是让我自己的html_instructions显示在我的应用程序上。我从http://www.coderzheaven.com/2019/02/19/complex-json-parsing-in-flutter-dart/开始尝试，但是无法解析，而且得到了：未处理的异常：类型'List'不是'String'类型的子类型
我期待着你们的启发，谢谢大家，祝你有美好的一天
答案 0 :(得分：0)
您可以在下面复制粘贴运行完整代码
代码段
Payload payload = payloadFromJson(jsonString);
print( ' ${payload.routes[0].legs[0].steps[0].distance.text}' );
print( ' ${payload.routes[0].legs[0].steps[0].steps[0].distance.text}' );
假设您的json字符串为
{
"geocoded_waypoints":[ ],
"routes":[
{
"bounds":{ },
"copyrights":"Map data ©2019 Google",
"legs":[
{
"arrival_time":{ },
"departure_time":{ },
"distance":{ },
"duration":{ },
"end_address":"dsfsfsdf32434324",
"end_location":{ },
"start_address":"123123123123adsfdsfsdfsd",
"start_location":{ },
"steps":[
{
"distance":{
"text":"55 m",
"value":55
},
"duration":{
"text":"1 min",
"value":52
},
"end_location":{
"lat":1.3775668,
"lng":103.8481395
},
"html_instructions":"Head" ,
"polyline":{
"points":"galGu|yxRH|@BZ"
},
"start_location":{
"lat":122,
"lng":1231
},
"travel_mode":"WALKING",
"steps":[
{
"distance":{
"text":"55 m",
"value":55
},
"duration":{
"text":"1 min",
"value":52
},
"end_location":{
"lat":1.3775668,
"lng":103.8481395
},
"html_instructions":"Head" ,
"polyline":{
"points":"galGu|yxRH|@BZ"
},
"start_location":{
"lat":122,
"lng":1231
},
"travel_mode":"WALKING"
}
]
}]
}]
}]
}
相关的解析类为
// To parse this JSON data, do
//
// final payload = payloadFromJson(jsonString);
import 'dart:convert';
Payload payloadFromJson(String str) => Payload.fromJson(json.decode(str));
String payloadToJson(Payload data) => json.encode(data.toJson());
class Payload {
List<dynamic> geocodedWaypoints;
List<Route> routes;
Payload({
this.geocodedWaypoints,
this.routes,
});
factory Payload.fromJson(Map<String, dynamic> json) => Payload(
geocodedWaypoints: List<dynamic>.from(json["geocoded_waypoints"].map((x) => x)),
routes: List<Route>.from(json["routes"].map((x) => Route.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"geocoded_waypoints": List<dynamic>.from(geocodedWaypoints.map((x) => x)),
"routes": List<dynamic>.from(routes.map((x) => x.toJson())),
};
}
class Route {
Bounds bounds;
String copyrights;
List<Leg> legs;
Route({
this.bounds,
this.copyrights,
this.legs,
});
factory Route.fromJson(Map<String, dynamic> json) => Route(
bounds: Bounds.fromJson(json["bounds"]),
copyrights: json["copyrights"],
legs: List<Leg>.from(json["legs"].map((x) => Leg.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"bounds": bounds.toJson(),
"copyrights": copyrights,
"legs": List<dynamic>.from(legs.map((x) => x.toJson())),
};
}
class Bounds {
Bounds();
factory Bounds.fromJson(Map<String, dynamic> json) => Bounds(
);
Map<String, dynamic> toJson() => {
};
}
class Leg {
Bounds arrivalTime;
Bounds departureTime;
Bounds distance;
Bounds duration;
String endAddress;
Bounds endLocation;
String startAddress;
Bounds startLocation;
List<Step> steps;
Leg({
this.arrivalTime,
this.departureTime,
this.distance,
this.duration,
this.endAddress,
this.endLocation,
this.startAddress,
this.startLocation,
this.steps,
});
factory Leg.fromJson(Map<String, dynamic> json) => Leg(
arrivalTime: Bounds.fromJson(json["arrival_time"]),
departureTime: Bounds.fromJson(json["departure_time"]),
distance: Bounds.fromJson(json["distance"]),
duration: Bounds.fromJson(json["duration"]),
endAddress: json["end_address"],
endLocation: Bounds.fromJson(json["end_location"]),
startAddress: json["start_address"],
startLocation: Bounds.fromJson(json["start_location"]),
steps: List<Step>.from(json["steps"].map((x) => Step.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"arrival_time": arrivalTime.toJson(),
"departure_time": departureTime.toJson(),
"distance": distance.toJson(),
"duration": duration.toJson(),
"end_address": endAddress,
"end_location": endLocation.toJson(),
"start_address": startAddress,
"start_location": startLocation.toJson(),
"steps": List<dynamic>.from(steps.map((x) => x.toJson())),
};
}
class Step {
Distance distance;
Distance duration;
Location endLocation;
String htmlInstructions;
Polyline polyline;
Location startLocation;
String travelMode;
List<Step> steps;
Step({
this.distance,
this.duration,
this.endLocation,
this.htmlInstructions,
this.polyline,
this.startLocation,
this.travelMode,
this.steps,
});
factory Step.fromJson(Map<String, dynamic> json) => Step(
distance: Distance.fromJson(json["distance"]),
duration: Distance.fromJson(json["duration"]),
endLocation: Location.fromJson(json["end_location"]),
htmlInstructions: json["html_instructions"],
polyline: Polyline.fromJson(json["polyline"]),
startLocation: Location.fromJson(json["start_location"]),
travelMode: json["travel_mode"],
steps: json["steps"] == null ? null : List<Step>.from(json["steps"].map((x) => Step.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"distance": distance.toJson(),
"duration": duration.toJson(),
"end_location": endLocation.toJson(),
"html_instructions": htmlInstructions,
"polyline": polyline.toJson(),
"start_location": startLocation.toJson(),
"travel_mode": travelMode,
"steps": steps == null ? null : List<dynamic>.from(steps.map((x) => x.toJson())),
};
}
class Distance {
String text;
int value;
Distance({
this.text,
this.value,
});
factory Distance.fromJson(Map<String, dynamic> json) => Distance(
text: json["text"],
value: json["value"],
);
Map<String, dynamic> toJson() => {
"text": text,
"value": value,
};
}
class Location {
double lat;
double lng;
Location({
this.lat,
this.lng,
});
factory Location.fromJson(Map<String, dynamic> json) => Location(
lat: json["lat"].toDouble(),
lng: json["lng"].toDouble(),
);
Map<String, dynamic> toJson() => {
"lat": lat,
"lng": lng,
};
}
class Polyline {
String points;
Polyline({
this.points,
});
factory Polyline.fromJson(Map<String, dynamic> json) => Polyline(
points: json["points"],
);
Map<String, dynamic> toJson() => {
"points": points,
};
}
完整代码
import 'package:flutter/material.dart';
// To parse this JSON data, do
//
// final payload = payloadFromJson(jsonString);
import 'dart:convert';
Payload payloadFromJson(String str) => Payload.fromJson(json.decode(str));
String payloadToJson(Payload data) => json.encode(data.toJson());
class Payload {
List<dynamic> geocodedWaypoints;
List<Route> routes;
Payload({
this.geocodedWaypoints,
this.routes,
});
factory Payload.fromJson(Map<String, dynamic> json) => Payload(
geocodedWaypoints: List<dynamic>.from(json["geocoded_waypoints"].map((x) => x)),
routes: List<Route>.from(json["routes"].map((x) => Route.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"geocoded_waypoints": List<dynamic>.from(geocodedWaypoints.map((x) => x)),
"routes": List<dynamic>.from(routes.map((x) => x.toJson())),
};
}
class Route {
Bounds bounds;
String copyrights;
List<Leg> legs;
Route({
this.bounds,
this.copyrights,
this.legs,
});
factory Route.fromJson(Map<String, dynamic> json) => Route(
bounds: Bounds.fromJson(json["bounds"]),
copyrights: json["copyrights"],
legs: List<Leg>.from(json["legs"].map((x) => Leg.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"bounds": bounds.toJson(),
"copyrights": copyrights,
"legs": List<dynamic>.from(legs.map((x) => x.toJson())),
};
}
class Bounds {
Bounds();
factory Bounds.fromJson(Map<String, dynamic> json) => Bounds(
);
Map<String, dynamic> toJson() => {
};
}
class Leg {
Bounds arrivalTime;
Bounds departureTime;
Bounds distance;
Bounds duration;
String endAddress;
Bounds endLocation;
String startAddress;
Bounds startLocation;
List<Step> steps;
Leg({
this.arrivalTime,
this.departureTime,
this.distance,
this.duration,
this.endAddress,
this.endLocation,
this.startAddress,
this.startLocation,
this.steps,
});
factory Leg.fromJson(Map<String, dynamic> json) => Leg(
arrivalTime: Bounds.fromJson(json["arrival_time"]),
departureTime: Bounds.fromJson(json["departure_time"]),
distance: Bounds.fromJson(json["distance"]),
duration: Bounds.fromJson(json["duration"]),
endAddress: json["end_address"],
endLocation: Bounds.fromJson(json["end_location"]),
startAddress: json["start_address"],
startLocation: Bounds.fromJson(json["start_location"]),
steps: List<Step>.from(json["steps"].map((x) => Step.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"arrival_time": arrivalTime.toJson(),
"departure_time": departureTime.toJson(),
"distance": distance.toJson(),
"duration": duration.toJson(),
"end_address": endAddress,
"end_location": endLocation.toJson(),
"start_address": startAddress,
"start_location": startLocation.toJson(),
"steps": List<dynamic>.from(steps.map((x) => x.toJson())),
};
}
class Step {
Distance distance;
Distance duration;
Location endLocation;
String htmlInstructions;
Polyline polyline;
Location startLocation;
String travelMode;
List<Step> steps;
Step({
this.distance,
this.duration,
this.endLocation,
this.htmlInstructions,
this.polyline,
this.startLocation,
this.travelMode,
this.steps,
});
factory Step.fromJson(Map<String, dynamic> json) => Step(
distance: Distance.fromJson(json["distance"]),
duration: Distance.fromJson(json["duration"]),
endLocation: Location.fromJson(json["end_location"]),
htmlInstructions: json["html_instructions"],
polyline: Polyline.fromJson(json["polyline"]),
startLocation: Location.fromJson(json["start_location"]),
travelMode: json["travel_mode"],
steps: json["steps"] == null ? null : List<Step>.from(json["steps"].map((x) => Step.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"distance": distance.toJson(),
"duration": duration.toJson(),
"end_location": endLocation.toJson(),
"html_instructions": htmlInstructions,
"polyline": polyline.toJson(),
"start_location": startLocation.toJson(),
"travel_mode": travelMode,
"steps": steps == null ? null : List<dynamic>.from(steps.map((x) => x.toJson())),
};
}
class Distance {
String text;
int value;
Distance({
this.text,
this.value,
});
factory Distance.fromJson(Map<String, dynamic> json) => Distance(
text: json["text"],
value: json["value"],
);
Map<String, dynamic> toJson() => {
"text": text,
"value": value,
};
}
class Location {
double lat;
double lng;
Location({
this.lat,
this.lng,
});
factory Location.fromJson(Map<String, dynamic> json) => Location(
lat: json["lat"].toDouble(),
lng: json["lng"].toDouble(),
);
Map<String, dynamic> toJson() => {
"lat": lat,
"lng": lng,
};
}
class Polyline {
String points;
Polyline({
this.points,
});
factory Polyline.fromJson(Map<String, dynamic> json) => Polyline(
points: json["points"],
);
Map<String, dynamic> toJson() => {
"points": points,
};
}
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
// This is the theme of your application.
//
// Try running your application with "flutter run". You'll see the
// application has a blue toolbar. Then, without quitting the app, try
// changing the primarySwatch below to Colors.green and then invoke
// "hot reload" (press "r" in the console where you ran "flutter run",
// or simply save your changes to "hot reload" in a Flutter IDE).
// Notice that the counter didn't reset back to zero; the application
// is not restarted.
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
// This widget is the home page of your application. It is stateful, meaning
// that it has a State object (defined below) that contains fields that affect
// how it looks.
// This class is the configuration for the state. It holds the values (in this
// case the title) provided by the parent (in this case the App widget) and
// used by the build method of the State. Fields in a Widget subclass are
// always marked "final".
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
String jsonString = '''
{
"geocoded_waypoints":[ ],
"routes":[
{
"bounds":{ },
"copyrights":"Map data ©2019 Google",
"legs":[
{
"arrival_time":{ },
"departure_time":{ },
"distance":{ },
"duration":{ },
"end_address":"dsfsfsdf32434324",
"end_location":{ },
"start_address":"123123123123adsfdsfsdfsd",
"start_location":{ },
"steps":[
{
"distance":{
"text":"55 m",
"value":55
},
"duration":{
"text":"1 min",
"value":52
},
"end_location":{
"lat":1.3775668,
"lng":103.8481395
},
"html_instructions":"Head" ,
"polyline":{
"points":"galGu|yxRH|@BZ"
},
"start_location":{
"lat":122,
"lng":1231
},
"travel_mode":"WALKING",
"steps":[
{
"distance":{
"text":"55 m",
"value":55
},
"duration":{
"text":"1 min",
"value":52
},
"end_location":{
"lat":1.3775668,
"lng":103.8481395
},
"html_instructions":"Head" ,
"polyline":{
"points":"galGu|yxRH|@BZ"
},
"start_location":{
"lat":122,
"lng":1231
},
"travel_mode":"WALKING"
}
]
}]
}]
}]
}
''';
void _incrementCounter() {
Payload payload = payloadFromJson(jsonString);
print( ' ${payload.routes[0].legs[0].steps[0].distance.text}' );
print( ' ${payload.routes[0].legs[0].steps[0].steps[0].distance.text}' );
setState(() {
// This call to setState tells the Flutter framework that something has
// changed in this State, which causes it to rerun the build method below
// so that the display can reflect the updated values. If we changed
// _counter without calling setState(), then the build method would not be
// called again, and so nothing would appear to happen.
_counter++;
});
}
@override
Widget build(BuildContext context) {
// This method is rerun every time setState is called, for instance as done
// by the _incrementCounter method above.
//
// The Flutter framework has been optimized to make rerunning build methods
// fast, so that you can just rebuild anything that needs updating rather
// than having to individually change instances of widgets.
return Scaffold(
appBar: AppBar(
// Here we take the value from the MyHomePage object that was created by
// the App.build method, and use it to set our appbar title.
title: Text(widget.title),
),
body: Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: Column(
// Column is also a layout widget. It takes a list of children and
// arranges them vertically. By default, it sizes itself to fit its
// children horizontally, and tries to be as tall as its parent.
//
// Invoke "debug painting" (press "p" in the console, choose the
// "Toggle Debug Paint" action from the Flutter Inspector in Android
// Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
// to see the wireframe for each widget.
//
// Column has various properties to control how it sizes itself and
// how it positions its children. Here we use mainAxisAlignment to
// center the children vertically; the main axis here is the vertical
// axis because Columns are vertical (the cross axis would be
// horizontal).
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}