Flutter/Dart JSON and serialization of an existing library class - json

Question

I have a class:
import 'package:google_maps_flutter/google_maps_flutter.dart';
class Place {
Place({
this.address,
this.coordinates,
});
final String address;
final LatLng coordinates;
}
LatLng is a class of google_maps_flutter. How can I make my Place class serializable using json_annotation and json_serializable?
Thank you very much!

Answer 1

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;
}

Answer 2

Put this code in your model
to get the information from JSON response simply do that after your request
final place = placeFromJson(response.body);
to get address => = place.address
to get coordinates => place.coordinates.lng , place.coordinates.lat
=============================================
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,
};
}

Answer 3

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;
}
}