jsonEncode generating error while converting object to jsonstring in flutter

Question

For explaining what I am facing problem while creating a jsonstring from object list,I have created this basic demo, actually I am trying to create a backup file for saving records but I am getting an error while jsonEncode.

getting following error

Converting object to an encodable object failed: Instance of 'TransactionModel'

class TransactionModel {
  String id;
  bool isexpense;
  DateTime date;
  double amount;

  TransactionModel({
    this.amount = 0.00,
    required this.id,
    this.isexpense = true,
    required this.date,
  });

  Map<String, dynamic> toJson() {
    return {
      'id': id,
      'isexpense': isexpense,
      'date': date,
      'amount': amount,
    };
  }
}

void main() {

  List<TransactionModel> trans = [
    TransactionModel(
      date: DateTime.now(),
        id: '1',),
  ];

  String result = jsonEncode(trans);//error bcz of jsonEncode

  print(result);
}

eamirho3ein · Accepted Answer · 2023-02-08 18:11:17Z

1

You can't encode an object with custom property like DateTime, you need first convert it to map, then encode it, try this:

void main() {

  List<TransactionModel> trans = [
    TransactionModel(
      date: DateTime.now(),
        id: '1',),
  ];

  var listOfMap = trans.map((e) => e.toJson()).toList();

  String result = jsonEncode(listOfMap);

  print(result);
}

edited Feb 8, 2023 at 18:11

answered Feb 8, 2023 at 17:38

eamirho3ein

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9 Comments

Irfan Ganatra Over a year ago

But I have already tried this

Irfan Ganatra Over a year ago

import 'dart:convert'; main() { User user = User('bezkoder', 21); String jsonUser = jsonEncode(user); print(jsonUser); }

eamirho3ein Over a year ago

I updated my answer, The example that you provide only works when you define TransactionModel with string or int or variable like that, not works with dateTime, if you want to use this kind of variable you need to convert it the way I answerd. @IrfanGanatra

eamirho3ein Over a year ago

The approach in that page won't works on dynamic classes as property, its only works when you use static type like string, int,... . @IrfanGanatra

Irfan Ganatra Over a year ago

Yes..I got your point and checked with editing date:date.toString() in my code and it worked....So converting to map is compulsory while using such datetime..

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