Datetime timezone deserialization

Question

I've developed a Rest API for my app. It sends to the app dates in the following format 2018-09-07T17:29:12+02:00, where I guess +2:00 represents my timezone as part of one object.

In my Flutter app, once I deserialize the received object, it substracts two hours to the actual received DateTime object.

The class I'm trying to deserialize is defined as follows:

import 'package:json_annotation/json_annotation.dart';

part 'evento.g.dart';

@JsonSerializable(nullable: false)
class Evento {
  final int id;
    final String nombre;
    final String discoteca;
    final int precio_desde;
    final int edad_minima;
    final DateTime fecha_inicio;
    final DateTime fecha_fin;
    final DateTime fecha_fin_acceso;
    final String cartel;
  final bool incluyeCopa;
    Evento(this.id, this.nombre, this.discoteca, this.precio_desde, this.edad_minima, this.fecha_inicio, this.fecha_fin, this.fecha_fin_acceso, this.cartel, this.incluyeCopa, this.num_tipos);
  factory Evento.fromJson(Map<String, dynamic> json) => _$EventoFromJson(json);
  Map<String, dynamic> toJson() => _$EventoToJson(this);
} 

Answer 1

DateTime can only represent local time and UTC time.

It supports timezone offset for parsing, but normalizes it to UTC

print(DateTime.parse('2018-09-07T17:29:12+02:00').isUtc);

prints true.

You can then only convert between local and UTC time using toLocal() or toUtc()

Answer 2

Try calling the .toLocal() method on the date when you deserialize it.

This is what the docs say

Use the methods toLocal and toUtc to get the equivalent date/time value specified in the other time zone.

Answer 3

One more way with json_serializable and freezed.

Create a class for converting DateTime.

import 'package:freezed_annotation/freezed_annotation.dart';

class DatetimeJsonConverter extends JsonConverter<DateTime, String> {
  const DatetimeJsonConverter();

  @override
  DateTime fromJson(String json) => DateTime.parse(json).toLocal();

  @override
  String toJson(DateTime object) => object.toUtc().toIso8601String();
}

After that just add it to every DateTime property in your classes.

@DatetimeJsonConverter() @JsonKey(name: 'created_at') required DateTime createdAt,

And it will be converted to Local\UTC time accordingly.