The Best Way to Parse a JSON in Dart

Flutter - The best way to parse a JSON

Compare this with things like quicktype: (1) If you do not have a model class, then try to use things like quicktype to get that class from a sample json string. (2) However, I suggest not to use the toJson and fromJson given by quicktype. The reason is that, when your model changes (say add a field / change a field), you must also change your toJson/fromJson accordingly (which is time-consuming and error-prone). Otherwise you get a bug.

If you already have your model class and only need the toJson and fromJson methods: Then the very famous json_serializable package suits you. It will happily generate the toJson and fromJson.

For example, say you have

class Person {
  final String firstName;
  final String lastName;
  final DateTime dateOfBirth;
}

Then with a bit of boilerplate code, it will auto give you

Person _$PersonFromJson(Map<String, dynamic> json) {
  return Person(
    firstName: json['firstName'] as String,
    lastName: json['lastName'] as String,
    dateOfBirth: DateTime.parse(json['dateOfBirth'] as String),
  );
}

Map<String, dynamic> _$PersonToJson(Person instance) => <String, dynamic>{
      'firstName': instance.firstName,
      'lastName': instance.lastName,
      'dateOfBirth': instance.dateOfBirth.toIso8601String(),
    };

Actually that package is more powerful than that. Check out the link for more details.

How to parse any json file in Dart?

Using the dart_convert library you can parse a json string to a map using Map<String, dynamic> yourMap = jsonDecode(jsonString);

Parsing JSON in Dart

The documentation is correct.

//if JSON is an array (starts with '[' )

List<Map> x = JSON.decode(responseText);
print(x[0]['title']);

//if JSON is not an array (starts with '{' )

Map z = JSON.decode(responseText);
print(z['content']);
print(z['id']);
print(z['title']);

Flutter how to parse JSON data

First thing the response from API is not a json list, its a simple json object.
If you wanna iterate over the keys of the above object you can create a list with all the keys and then use key index to get the actual key name in the response.

final List<String> keys = ["alm","co2","hu","temp","th","tm","ts"];

then you can modify your body widget like following -

body: new ListView.builder(
        itemCount: data == null ? 0 : data.length,
        itemBuilder: (BuildContext context, int index) {
          return new ListTile(
            leading: const Icon(Icons.stay_primary_portrait),
            title: Text(data.length.toString()),
            subtitle: Text(data[keys[index]]),
            trailing: Icon(Icons.more_vert),
            dense: true,
            isThreeLine: true,
          );
        },
      ),

Hope this helps!

How to parse complex JSON using default methods in Flutter?

To work with JSON objects that have deep/multiple levels/recursive dot notation, then you can use a fantastic Dart package: g_json. I find it super easy and simple!

It doesn't use generated code as on Flutter recommended packages for JSON and these are complicated. Dart & Flutter teams have to improve.

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I use a complex JSON object and your example and I show you how I access the data (you have to clean your JSON string, maybe your example is copied from a place that add extra double quotes " " on brackets).

Now, look at my code:

import 'dart:convert';
import 'package:g_json/g_json.dart';

void main() {
  String jsonSimple = '{"a":"1"}';

  // Get value from only one level JSON object.
  final Map<String, dynamic> resultSimple = json.decode(jsonSimple);
  print(resultSimple);

  // Your example with some cleaning.
  String jsonExample = jsonEncode({
    "a": {"b": 7}
  });
  var resultDeep = JSON.parse(jsonExample);
  print(resultDeep['a']['b'].rawString());

  // Deep JSON object
  // This is a real JSON data from api.openweathermap.org/data/2.5/weather?q=Barcelona&appid=<your_api_key>. You can try it on your browser, put it on the url and press `ENTER`.
  String jsonWeather = jsonEncode({
    "coord": {"lon": 2.159, "lat": 41.3888},
    "weather": [
      {
        "id": 803,
        "main": "Clouds",
        "description": "broken clouds",
        "icon": "04d"
      }
    ],
    "base": "stations",
    "main": {
      "temp": 291.21,
      "feels_like": 291.11,
      "temp_min": 289.53,
      "temp_max": 293.62,
      "pressure": 1016,
      "humidity": 78
    },
    "visibility": 10000,
    "wind": {"speed": 0.45, "deg": 212, "gust": 1.79},
    "clouds": {"all": 75},
    "dt": 1633360018,
    "sys": {
      "type": 2,
      "id": 18549,
      "country": "ES",
      "sunrise": 1633326668,
      "sunset": 1633368526
    },
    "timezone": 7200,
    "id": 3128760,
    "name": "Barcelona",
    "cod": 200
  });
  print(jsonWeather);
  // It prints: `String`
  print(jsonWeather.runtimeType);
  resultDeep = JSON.parse(jsonWeather);
  print(resultDeep['wind']['speed'].rawString());
  print(resultDeep['weather'][0]['main'].rawString());

  // Extract data for each item of the array.
  final List<dynamic> listJsonWeather = resultDeep['weather'].value;
  List<WeatherEntity> listWeathers = [];
  for (dynamic jsonWeather in listJsonWeather) {
    listWeathers.add(WeatherEntity(
      id: jsonWeather['id'].toString(),
      title: jsonWeather['main'] as String,
      overview: jsonWeather['description'] as String,
      image: '<url>/${jsonWeather['icon']}',
    ));
  }
}

The console prints the next outcome:

7
String
0.45
"Clouds"

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Tips

You can use Postman to fetch API data from services. A very useful tool, trust me!

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