Parsing a json in flutter

Question

I have this json that I am fetching from firebase realtime database

 [{image: https://cdn.searchenginejournal.com/wp-content/uploads/2019/07/the-essential-guide-to-using-images-legally-online-1520x800.png, shopId: 1}, 
{image: https://cdn.searchenginejournal.com/wp-content/uploads/2019/07/the-essential-guide-to-using-images-legally-online-1520x800.png, shopId: 2}]

When I try to parse it, I am receiving different errors: First way:

List<HomeSlider> posts = List<HomeSlider>.from(l.map((model)=> HomeSlider.fromJson(model)));

imgList.addAll(List<HomeSlider>.from(data.value) => HomeSlider.HomeSlider.fromJson(json));

Second way:

      Map<dynamic, dynamic> yearMap = data.value;
  yearMap.forEach((key, value) {
     imgList.add(HomeSlider.fromJson(value));
  });

I have the home slider object:

    import 'package:json_annotation/json_annotation.dart';

/// This allows the `User` class to access private members in
/// the generated file. The value for this is *.g.dart, where
/// the star denotes the source file name.
part 'HomeSlider.g.dart';

@JsonSerializable()
class HomeSlider{

  HomeSlider(this.image, this.shopId);
  String image="";
  String shopId="";

  /// A necessary factory constructor for creating a new User instance
  /// from a map. Pass the map to the generated `_$UserFromJson()` constructor.
  /// The constructor is named after the source class, in this case, User.
  factory HomeSlider.fromJson(Map<String, dynamic> json) => _$HomeSliderFromJson(json);

  /// `toJson` is the convention for a class to declare support for serialization
  /// to JSON. The implementation simply calls the private, generated
  /// helper method `_$UserToJson`.
  Map<String, dynamic> toJson() => _$HomeSliderToJson(this);

}

Errors are: 'String' is not a subtype of type 'Map<String, dynamic>' or w json exception if I try to encode it

I have generated the class as by the documentation using flutter CLI Any suggestions? Thanks

I am getting it from firebase as a string. How to parse the data received from firebase into a list of objects? — Miriana Itani
– Miriana Itani, Commented Aug 28, 2021 at 18:57

ZeRj · Accepted Answer · 2021-08-29 10:00:18Z

1

First: Your Json looks wrong, it's missing the double quotes:

[{"image": "https://cdn.searchenginejournal.com/wp-content/uploads/2019/07/the-essential-guide-to-using-images-legally-online-1520x800.png", "shopId": 1}, 
{"image": "https://cdn.searchenginejournal.com/wp-content/uploads/2019/07/the-essential-guide-to-using-images-legally-online-1520x800.png", "shopId": 2}]

Second: In your Model shopId probably should be an int. If string is intended, you also need to put the id in double quotes.

Then use jsonDecode to convert the String into a List<Map<String,dynamic>> and convert it like that:

  List<HomeSlider> homeSliderList;
  homeSliderList= (jsonDecode(yourJsonString) as List)
      .map((i) => HomeSlider.fromJson(i))
      .toList();

edited Aug 29, 2021 at 10:00

answered Aug 27, 2021 at 17:47

ZeRj

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3 Comments

Miriana Itani Over a year ago

jsonDecode(jsonEncode(content)) I tried to encode the json but still not working. I will post the different errors

Miriana Itani Over a year ago

Dart Unhandled Exception: FormatException: Unexpected character (at character 2). I think there is a problem with the json returned from firebase. For some reason, firebase is not returning it with the proper format

Miriana Itani Over a year ago

I just encoded the json string before. Thanks

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