The class 'List' doesn't have a constructor named 'fromJson'. Try invoking a different constructor, or define a constructor named 'fromJson'

Question

class Product {
    String status;
    List<List> note;
    List<List> table;

    Product({this.status, this.note, this.table});

    Product.fromJson(Map<String, dynamic> json) {
        status = json['status'];
        if (json['note'] != null) {
            note = <List>[];
            json['note'].forEach((v) { note.add(new List.fromJson(v)); });
        }
        if (json['table'] != null) {
            table = <List>[];
            json['table'].forEach((v) { table.add(new List.fromJson(v)); });
        }
    }

    Map<String, dynamic> toJson() {
        final Map<String, dynamic> data = new Map<String, dynamic>();
        data['status'] = this.status;
        if (this.note != null) {
      data['note'] = this.note.map((v) => v.toJson()).toList();
    }
        if (this.table != null) {
      data['table'] = this.table.map((v) => v.toJson()).toList();
    }
        return data;
    }
}

The class 'List' doesn't have a constructor named 'fromJson'. Try invoking a different constructor, or define a constructor named 'fromJson'. / Error in List.fromJson and v.toJson

score 0 · Answer 1 · answered Sep 16 '21 at 06:48

The error message says it pretty straightforward.

you can not call

new List.fromJson(v)

Try to create a dart Iterable from your json and use .from() constructor

List<E>.from(
Iterable elements,
{bool growable = true}
)

Or try other constructors defined by the List Class https://api.dart.dev/stable/2.14.2/dart-core/List-class.html

This lib might also be helpful https://pub.dev/packages/json_serializable

Jahidul Islam · Answer 2 · 2021-09-16T06:58:57.337

The list is an abstract class. It has not a constructor fromJson. If you want to convert from JSON into list, you must assign a list with Elements (Note) Like:

//Generic form 
List<E>
// For note 
List<Note> note;
// call like that
json['note'].forEach((v) { note.add(new Note.fromJson(v)); });

Model class of Note:

class Note {
  String title;
  String description;

  Note({this.title, this.description});

  Note.fromJson(Map<String, dynamic> json) {
    title = json['title'];
    description = json['description'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['title'] = this.title;
    data['description'] = this.description;
    return data;
  }
}

The class 'List' doesn't have a constructor named 'fromJson'. Try invoking a different constructor, or define a constructor named 'fromJson'

2 Answers2