I need to solve FormatException: Unexpected character Flutter? - flutter

Question

Hi everyone I got this exception (Unexpected character ) when I call this json.decode(jsonString), but some times when I run the app it doesn't throw any exception .
when this exception appear the expect data that comes from server doesn't displayed on the app .
I test my API in localhost .
my code :
Future<List<Governorate>> getGovernorates() async {
var governorates = List<Governorate>();
var governorate = await client.get('$endpoint/governorates');
String jsonString = governorate.body?.toString();
if(governorate.statusCode == 200){
//print("governorate =====> ${jsonString}");
var parsed= json.decode(jsonString) as List<dynamic>; // sometimes it's fails here and throw the exeption FormatException: Unexpected character
for(var gov in parsed){
governorates.add(Governorate.fromJson(gov));
}
} else {
throw "Can't get governorates";
}
return governorates;
}
json object :
[
{
"id": 1,
"governorate_name": "test governorate",
"governorate_cities": []
},
{
"id": 1,
"governorate_name": "test governorate 2",
"governorate_cities": [
{
"id": 11,
"city_name": "test city",
"governorate_id": 1
}
]
}
]
I try to solve this problem but I don't success I hope you guys give my the Idea about this problem and how can I solve it
Thanks for your attention. I’m looking forward to your answer.

Answer 1

Just check out the code that I have implemented based on your json provided.
This is the json you provided.
[
{
"id":1,
"governorate_name":"test governorate",
"governorate_cities":[
]
},
{
"id":1,
"governorate_name":"test governorate 2",
"governorate_cities":[
{
"id":11,
"city_name":"test city",
"governorate_id":1
}
]
}
]
And from the above json I have created a model class for it just check it out
// To parse this JSON data, do
//
// final governorate = governorateFromJson(jsonString);
import 'dart:convert';
List<Governorate> governorateFromJson(String str) => List<Governorate>.from(json.decode(str).map((x) => Governorate.fromJson(x)));
String governorateToJson(List<Governorate> data) => json.encode(List<dynamic>.from(data.map((x) => x.toJson())));
class Governorate {
Governorate({
this.id,
this.governorateName,
this.governorateCities,
});
int id;
String governorateName;
List<GovernorateCity> governorateCities;
factory Governorate.fromJson(Map<String, dynamic> json) => Governorate(
id: json["id"],
governorateName: json["governorate_name"],
governorateCities: List<GovernorateCity>.from(json["governorate_cities"].map((x) => GovernorateCity.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"id": id,
"governorate_name": governorateName,
"governorate_cities": List<dynamic>.from(governorateCities.map((x) => x.toJson())),
};
}
class GovernorateCity {
GovernorateCity({
this.id,
this.cityName,
this.governorateId,
});
int id;
String cityName;
int governorateId;
factory GovernorateCity.fromJson(Map<String, dynamic> json) => GovernorateCity(
id: json["id"],
cityName: json["city_name"],
governorateId: json["governorate_id"],
);
Map<String, dynamic> toJson() => {
"id": id,
"city_name": cityName,
"governorate_id": governorateId,
};
}
And this is where I have shown a sample ui in the listview for the name.
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:json_parsing_example/models.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(title: 'Users'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
bool _isLoading = false;
List<Governorate> dataList = List();
Future<String> loadFromAssets() async {
return await rootBundle.loadString('json/parse.json');
}
#override
void initState() {
super.initState();
getData();
}
getData() async {
setState(() {
_isLoading = true;
});
String jsonString = await loadFromAssets();
final governorate = governorateFromJson(jsonString);
dataList = governorate;
setState(() {
_isLoading = false;
});
}
/*
// This will be in your case as per you code
Future<List<Governorate>> getGovernorates() async {
var governorates = List<Governorate>();
var governorate = await client.get('$endpoint/governorates');
String jsonString = governorate.body?.toString();
if(governorate.statusCode == 200){
return governorateFromJson(jsonString);
}
} */
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
),
body: _isLoading
? Center(
child: CircularProgressIndicator(),
)
: Container(
child: ListView.builder(
itemCount: dataList.length,
shrinkWrap: true,
itemBuilder: (context, i) {
return Card(
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Text(dataList[i].governorateName),
));
}),
),
);
}
}
This might happen because the list is empty just check the following code and let me know still the error occurs
Change the following factory method from the model class
factory NewMessagesModel.fromJson(Map<String, dynamic> json) => NewMessagesModel(
id: json["id"],
governorateName: json["governorate_name"],
governorateCities: json["governorate_cities"] ==null ?null:List<GovernorateCity>.from(json["governorate_cities"].map((x) => GovernorateCity.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"id": id,
"governorate_name": governorateName,
"governorate_cities":json["governorate_cities"] ==null?null : List<dynamic>.from(governorateCities.map((x) => x.toJson())),
};
}
just check the commented code where I have taken you api fetching code and made some modifications so that it would work and let me know if it works.