Convert List to Json String then Convert this String back to List in Dart

Question

I want to convert a list List<Word> myListto String and put it into sharedPreference and later I also want to convert that string (from sharedPreference) back to List<Word>.

Here is my model class Word

class Word {
  int id;
  String word;
  String meaning;
  String fillInTheGapSentence;

  Word.empty();

  Word(int id, String word, String meaning, String fillInTheGapSentence){
    this.id = id;
    this.word = word;
    this.meaning = meaning;
    this.fillInTheGapSentence = fillInTheGapSentence;
  }
}

I can convert the List<Word> myList to String like this

var myListString = myList.toString();

But couldn't make List<Word> myListFromString from myListString.

Thanks.

Solution

First of all, myList.toString() is not in JSON format, unless you override toString() method. What you have to do is manually transform the object into a Dictionary then encoded it to JSON string. In reverse, you need to convert the string into a dictionary, then transform it into an object. Something like this:

import 'dart:convert';

class Word {
  int id;
  String word;
  String meaning;
  String fillInTheGapSentence;

  Word.empty();

  Word(int id, String word, String meaning, String fillInTheGapSentence) {
    this.id = id;
    this.word = word;
    this.meaning = meaning;
    this.fillInTheGapSentence = fillInTheGapSentence;
  }

  Map<String, dynamic> toMap() {
    return {
      'id': this.id,
      'word': this.word,
      'meaning': this.meaning,
      'fillInTheGapSentence': this.fillInTheGapSentence,
    };
  }

  factory Word.fromMap(Map<String, dynamic> map) {
    return new Word(
      map['id'] as int,
      map['word'] as String,
      map['meaning'] as String,
      map['fillInTheGapSentence'] as String,
    );
  }
}

String convertToJson(List<Word> words) {
  List<Map<String, dynamic>> jsonData =
      words.map((word) => word.toMap()).toList();
  return jsonEncode(jsonData);
}

List<Word> fromJSon(String json) {
  List<Map<String, dynamic>> jsonData = jsonDecode(json);
  return jsonData.map((map) => Word.fromMap(map)).toList();
}

Comments

[sj_959]

Thanks a lot! I got my code to work with a few tweaks in yours. (Specifically the List<Map<String, dynamic>> part in fromJson)

[Al Walid Ashik]

awesome @sj_959