Arguments are missing in constructor of TypeAdapter from extended class

[giandifra]

Steps to Reproduce
I have created TypeAdapter from this comment to use extended class.

Code sample
pet.dart

import 'package:hive/hive.dart';

class Pet extends Equatable {
  @HiveField(0)
  final String name;

  @HiveField(1)
  final int age;

  Pet(this.name, this.age);

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

dog.dart

import 'package:hive/hive.dart';
import 'pet.dart';

part 'dog.g.dart';

@HiveType(typeId: 1)
class Dog extends Pet {
  Dog(String name, int age) : super(name, age);
}

dog.g.dart

// GENERATED CODE - DO NOT MODIFY BY HAND

part of 'dog.dart';

// **************************************************************************
// TypeAdapterGenerator
// **************************************************************************

class DogAdapter extends TypeAdapter<Dog> {
  @override
  final typeId = 1;

  @override
  Dog read(BinaryReader reader) {
    var numOfFields = reader.readByte();
    var fields = <int, dynamic>{
      for (var i = 0; i < numOfFields; i++) reader.readByte(): reader.read(),
    };
    return Dog();
  }

  @override
  void write(BinaryWriter writer, Dog obj) {
    writer
      ..writeByte(2)
      ..writeByte(0)
      ..write(obj.name)
      ..writeByte(1)
      ..write(obj.age);
  }
}

How you can see, there is an error in the constructor of Dog in TypeAdapter, arguments are missing.

Version

• Flutter version: 1.15.2-pre.36
• Flutter channel: master
• hive: ^1.4.0+1
• hive_flutter: ^0.3.0+1
• hive_generator: ^0.7.0

[simc]

Unfortunately, only zero-argument constructors and constructors which use Initializing parameters (like "Pet(this.name, this.age)") can be used.

[yringler]

I just stumbled into this.
For others who see this: that just means that a base class has to be non-final, and either have no constructor or a constructor with no arguments.
I do like my finals, but not too bad.

[mohammadne]

my problem is that I am using JsonSerializable for my classes and if I not specify the constructor, I will get
The class `Pet` has no default constructor.
so I have to use constructor for that.

any help is appreciated.

[mohammadne]

is there any way to fix the constructor issue ?

[yringler]

If you don't specify a constructor, then there's an implicit default constructor. Can you paste your class?

[mohammadne]

If you don't specify a constructor, then there's an implicit default constructor. Can you paste your class?

#442 (comment)

[themisir]

Duplicate of #442

[qwertie]

@simc I'm struggling to figure out how to migrate old data into a new object format. You say only this. parameters can be used, but the documentation says that "Fields can be...changed from public to private or vice versa". But the compiler rejects this._foo as a constructor parameter, so it would seem that making fields private is impossible. I guess I have to use fields with names like private_foo? And apparently I will also need to have fields that aren't used - fields whose only purpose is to be migrated in the constructor, and are never used after that. They should be normal constructor parameters, not fields, but this isn't allowed? This is poor UX (for developers) and wastes memory.

Moreover, it looks like certain fields that should be final must be mutable so that the constructor can change them, since a parameter x cannot use both this.x syntax and : x = expr syntax at the same time. And presumably it is also not possible to use a factory constructor like MyClass.fromHive() for the migration code, since factory constructors don't use "this." parameters.