flutter - Comparing two lists of objects isn't working

Question

I've two lists of objects that i wanna compare, a and b:

final dia = DateTime(2017, 9, 7, 17, 30);
final ppp = Parcela("1", 225.5, dia, null, 1, false, false);
final ppp2 =Parcela("1", 225, dia.add(const Duration(days: 3)), null, 1, false, false);
final ppp3 =Parcela("1", 225, dia.add(const Duration(days: 3)), null, 1, false, false);
List<Parcela> a = [ppp,ppp2,];
List<Parcela> b = [ppp, ppp3];

Both of them are equal, but when i try to check it with the functions bellow i get false on response:

print(a.every(b.toSet().contains));
print(listEquals(a, b));

I tried also "quiver" and "collection" libraries from pub dev but the result is the same

The Parcela model:

class Parcela {
  String id;
  double valor;
  DateTime dataPagamento;
  DateTime dataPago;
  int status;
  int ref;

  Parcela(String id, double valor, DateTime dataPagamento, DateTime dataPago,
      int ref, bool pago, bool atraso) {
    this.id = id;
    this.valor = valor;
    this.dataPagamento = dataPagamento;
    this.dataPago = this.dataPago;
    this.status = _getStatus(pago, atraso);
    this.ref = this.ref;
  }
  int _getStatus(bool pago, bool atraso) {
    if (pago) {
      if (atraso) {
        return 3;
      } else {
        return 1;
      }
    } else {
      if (atraso) {
        return 2;
      } else {
        return 0;
      }
    }
  }
}

Edit1:

I've tried Dan James suggestion but my class isn't final as his, so i've removed "final" from name attribute:

class Person extends Equatable {
   Person(this.name);

   String name;

  @override
  List<Object> get props => [name];

}

the new test vars:

Person p = Person("name");
Person p2 = Person("name2");
Person p3 = Person("tobias");

List<Person> aa = [p, p2];
List<Person> bb = [p, p2..name = "teste"];
List<Person> cc = [p, p3];

but when i test the lists:

var filtered_lst =List.from(aa.where((value) => !bb.contains(value)));
print(filtered_lst);
print(listEquals(aa, bb));
print(listEquals(aa, cc));

the console returns this:

I/flutter (12746): []
I/flutter (12746): true
I/flutter (12746): false

Dan James · Accepted Answer · 2021-05-15 18:26:08Z

2

ppp2 does not equal ppp3 because they are two different instances of a class. You could override the '==' operator to check if each field is the same. ie. ppp2.id == ppp3.id.

eg/ (taken from equatable docs but this is vanillar dart)

class Person {
  const Person(this.name);

  final String name;

  @override
  bool operator ==(Object other) =>
    identical(this, other) ||
    other is Person &&
    runtimeType == other.runtimeType &&
    name == other.name;

  @override
  int get hashCode => name.hashCode;
}

Or look into the equatable package which does this for you. https://pub.dev/packages/equatable

Straight from the equatable docs:

import 'package:equatable/equatable.dart';

class Person extends Equatable {
  const Person(this.name);

  final String name;

  @override
  List<Object> get props => [name];

}

edited May 15, 2021 at 18:26

answered May 15, 2021 at 18:24

Dan James

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6 Comments

Gianluca Bettega Over a year ago

can you add a sample code to your answer?

Gianluca Bettega Over a year ago

your solution doesn't work: Person p = Person("name"); Person p2 = Person("name2"); List<Person> aa = [p, p2]; List<Person> bb = [p, p2..name = "teste"]; print(listEquals(aa, bb)); returns true

enzo Over a year ago

It's returning true in the first comparison because when you do p2..name = "teste" you're also modifying the p2 object inside aa, so aa and bb will be true.

Gianluca Bettega Over a year ago

Is there any way of generating a copy of another list that doesn't point to the same address of memory?

Dan James Over a year ago

using the spread operator is an easy way to create a new list. eg/. List list2 = [...list1];

|

Gianluca Bettega · Accepted Answer · 2021-06-02 22:56:01Z

Using the library equatable from Dan James answer:

import 'package:equatable/equatable.dart';

// ignore: must_be_immutable
class Parcela extends Equatable {
  String id;
  double valor;
  DateTime dataPagamento;
  DateTime dataPago;
  int status;
  int ref;

  Parcela(String id, double valor, DateTime dataPagamento, DateTime dataPago,
      int ref, bool pago, bool atraso) {
    this.id = id;
    this.valor = valor;
    this.dataPagamento = dataPagamento;
    this.dataPago = this.dataPago;
    this.status = _getStatus(pago, atraso);
    this.ref = this.ref;
  }
  int _getStatus(bool pago, bool atraso) {
    if (pago) {
      if (atraso) {
        return 3;
      } else {
        return 2;
      }
    } else {
      if (atraso) {
        return 1;
      } else {
        return 0;
      }
    }
  }
  @override
  List<Object> get props => [id,valor,dataPagamento,];
}

The only way of copying a list that doesn't point to the same memory address:

List<Parcela> copyParcelas(List<Parcela> list) {
  List<Parcela> copyList = [];
  for (var item in list) {
    List<bool> _status = pagoAtraso(item.status);
    Parcela betItems = Parcela(item.id, item.valor, item.dataPagamento,
        item.dataPago, item.ref, _status[0], _status[1]);
    copyList.add(betItems);
  }
  return copyList;
}

Then the check to return the list items that changed:

List<Parcela> editarParcelas(List<Parcela> parcelas, List<Parcela> original){
    return filteredlst = parcelas.toSet().difference(original.toSet()).toList();
}

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