Put this code in your model

to get the information from JSON response simply do that after your request

1. final place = placeFromJson(response.body);
2. to get address => = place.address
3. to get coordinates => place.coordinates.lng , place.coordinates.lat

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import 'dart:convert';Place placeFromJson(String str) => Place.fromJson(json.decode(str));String placeToJson(Place data) => json.encode(data.toJson());class Place {    String address;    Coordinates coordinates;    Place({        this.address,        this.coordinates,    });    factory Place.fromJson(Map<String, dynamic> json) => Place(        address: json["address"],        coordinates: Coordinates.fromJson(json["coordinates"]),    );    Map<String, dynamic> toJson() => {        "address": address,        "coordinates": coordinates.toJson(),    };}class Coordinates {    String lat;    String lng;    Coordinates({        this.lat,        this.lng,    });    factory Coordinates.fromJson(Map<String, dynamic> json) => Coordinates(        lat: json["lat"],        lng: json["lng"],    );    Map<String, dynamic> toJson() => {        "lat": lat,        "lng": lng,    };}

You can explicitly specify which methods of LatLng should be used for serialization using JsonKey annotation:

@JsonSerializable()class Place {  Place({    this.address,    this.coordinates,  });  final String address;  @JsonKey(fromJson: LatLng.fromJson, toJson: jsonEncode)  final LatLng coordinates;}

I didn't find a super easy solution for this. I ended up, writing a custom toJson/fromJson for the LatLng property. I've put it statically onto my model, but you could also create a global function, if you need to reuse it.

Take care, that in my example LatLng is nullable.

import 'dart:collection';import 'dart:convert';import 'package:latlong2/latlong.dart';part 'challenge_model.g.dart';@JsonSerializable()class ChallengeModel with _$ChallengeModel {  ChallengeModel({    required this.startPosition,  });  @override  @JsonKey(fromJson: latLngFromJson, toJson: latLngToJson)  final LatLng? startPosition;  /// Create [ChallengeModel] from a json representation  static fromJson(Map<String, dynamic> json) => _$ChallengeModelFromJson(json);  /// Json representation  @override  Map<String, dynamic> toJson() => _$ChallengeModelToJson(this);  static String latLngToJson(LatLng? latLng) =>      jsonEncode(latLng != null ? {'latitude': latLng.latitude, 'longitude': latLng.longitude} : null);  static LatLng? latLngFromJson(String jsonString) {    final LinkedHashMap<String, dynamic>? jsonMap = jsonDecode(jsonString);    return jsonMap != null ? LatLng(jsonMap['latitude'], jsonMap['longitude']) : null;  }}