Handling null value inside Map - api

Question

I'm learning to use BLOC pattern for consume API from newsapi.org. I have result JSON and Model like this from https://newsapi.org/v2/everythingq=flutter&apiKey=7f8eef4261bc4c29b26c4d5e93e8b5d6:
Json
{
"status": "ok",
"totalResults": 533,
"articles": [
{
"source": {
"id": "cnn",
"name": "CNN"
},
"author": "Sandee LaMotte, CNN",
"title": "Burnout linked to potentially deadly irregular heartbeat, study says",
"description": "If you're feeling bone-deep mental and physical exhaustion, or what is otherwise known as burnout, new research suggests you could be at a higher risk for a potentially fatal heart flutter.",
"url": "https://www.cnn.com/2020/01/13/health/burnout-linked-to-atrial-fibrillation-wellness/index.html",
"urlToImage": "https://cdn.cnn.com/cnnnext/dam/assets/200113120102-02-burnout-stock-super-tease.jpg",
"publishedAt": "2020-01-14T00:15:07Z",
"content": "(CNN)If you're feeling bone-deep mental and physical exhaustion, or what is otherwise known as burnout, new research suggests you could be at a higher risk for a potentially fatal heart flutter.\r\nAtrial fibrillation, also called AFib or AF, is the most common… [+4971 chars]"
},
{
"source": {
"id": "the-verge",
"name": "The Verge"
},
"author": "Ashley Carman",
"title": "The sex toy banned from CES last year is unlike anything we’ve ever seen",
"description": "Lora DiCarlo’s Osé personal massager made it to CES this year, after being banned and having its award revoked in 2019. The device is certainly innovative, using suction and movement to stimulate the G-spot and clitoris instead of vibration.",
"url": "https://www.theverge.com/2020/1/6/21051259/lora-dicarlo-sex-tech-toy-massager-awards-ban-ose-ces-2020",
"urlToImage": "https://cdn.vox-cdn.com/thumbor/G5zPZiQZgwqS9FqLqzUE3eyyLyA=/0x146:2040x1214/fit-in/1200x630/cdn.vox-cdn.com/uploads/chorus_asset/file/19576504/loradicarlo1.jpg",
"publishedAt": "2020-01-06T14:25:23Z",
"content": "Its certainly innovative\r\nAshley Carman / The Verge\r\nLora DiCarlo likely didnt intend to change CES forever, but the sexual wellness company and its personal massager accomplished just that last year. After having an award revoked and being banned from the sh… [+3125 chars]"
},
{
"source": {
"id": null,
"name": "Codemagic.io"
},
"author": null,
"title": "Flutter vs. Other Mobile Development Frameworks: A UI and Performance Experiment",
"description": "In this experiment we created the same app five times, each time with a different framework. The frameworks I used were native Android, native iOS, Flutter, Xamarin Forms and React Native",
"url": "https://blog.codemagic.io/flutter-vs-ios-android-reactnative-xamarin/",
"urlToImage": "https://blog.codemagic.io/uploads/Codemagic-io_Blog_Flutter-Versus-Other-Mobile-Development-Frameworks_1.png",
"publishedAt": "2020-01-03T21:26:48Z",
"content": "Written by Bram De Coninck\r\nIve already read a lot of articles about how Flutter compares to other mobile development frameworks, but most of them were written from a theoretical point of view. Its already been well established that Flutter is a solid choice … [+24309 chars]"
},
{
"source": {
"id": null,
"name": "Insider.com"
},
"author": "dschild#businessinsider.com (Darcy Schild), Darcy Schild",
"title": "Kylie Jenner shared a sneak peek of her new makeup collection inspired by her daughter, Stormi",
"description": "Kylie Jenner/YouTube; Kylie Jenner/Instagram Kylie Jenner, the makeup mogul behind Kylie Cosmetics, is launching a collection of new eyeshadows, Lip Kits, lip glosses, and a blush inspired by her 1-year-old daughter, Stormi. Jenner gave her followers a sneak …",
"url": "https://www.insider.com/kylie-jenner-cosmetics-stormi-collection-when-to-buy-2020-1",
"urlToImage": "https://i.insider.com/5e24bb4b3ac0c9452948fd10?width=1200&format=jpeg",
"publishedAt": "2020-01-19T20:24:58Z",
"content": "Kylie Jenner is launching a makeup collection inspired by her 1-year-old daughter, Stormi Webster.\r\nThe Stormi Collection by Kylie Cosmetics will be available for purchase starting February 1, Jenner said in an Instagram Story post on Saturday.\r\nIn November 2… [+2710 chars]"
},
]
}
NewsModel
class NewsModel {
final Map<String, dynamic> source;
final String author;
final String title;
final String description;
final String url;
final String urlToImage;
final String publishedAt;
final String content;
NewsModel({
this.source,
this.author,
this.title,
this.description,
this.url,
this.urlToImage,
this.publishedAt,
this.content,
});
NewsModel.fromJson(Map<String, dynamic> parsedJson)
: source = parsedJson['source']== null
? "Unknown Source"
: parsedJson['source'],
author = parsedJson['author'] == null
? "Unknown Author"
: parsedJson['author'],
title =
parsedJson['title'] == null ? "Unknown Title" : parsedJson['title'],
description = parsedJson['description'] == null
? "Unknown Description"
: parsedJson['description'],
url = parsedJson['url'] == null ? "Unknown Url" : parsedJson['url'],
urlToImage = parsedJson['urlToImage'] == null
? "https://homepages.cae.wisc.edu/~ece533/images/peppers.png"
: parsedJson['urlToImage'],
publishedAt = parsedJson['publishedAt'] == null
? "Unknown PublishedAt"
: parsedJson['publishedAt'],
content = parsedJson['content'] == null
? "Unknown Content"
: parsedJson['content'];
Map<String, dynamic> toMapForDb() {
return <String, dynamic>{
"source": source,
"author": author,
"title": title,
"description": description,
"url": url,
"urlToImage": urlToImage,
"publishedAt": publishedAt,
"content": content,
};
}
}
final newsModel = NewsModel();
source in this json is MAP,But one of its value is null (id). How to handling null value in my model ?
I'm trying handling this null value like this
source = parsedJson['source']['id'] == null? "Unknown Source" : parsedJson['source'],
But i get the error message Error From Bloc =type 'String' is not a subtype of type Map<String, dynamic>
My temporary solution to handling null value return Text(news.source["id"] ?? "null"); . But i want handling inside my model.
If you need BLOC source code
BLOC
import 'package:network/models/news_model.dart';
import 'package:repositories/repositories/news_repositories.dart';
import 'package:rxdart/subjects.dart';
class NewsBloc {
final _newsRepositories = NewsRepositories();
final _newsFetch = PublishSubject<List<NewsModel>>();
Stream<List<NewsModel>> get allEverythingNews => _newsFetch.stream;
Future<void> getEverythingNews() async {
try {
List<NewsModel> news = await _newsRepositories.getNewsEverything();
final newsAddSink = _newsFetch.sink.add(news);
return newsAddSink;
} catch (e) {
print("Error From Bloc =" + e.toString());
_newsFetch.sink.addError(e);
}
}
void dispose() {
_newsFetch.close();
}
}
final newsBloc = NewsBloc();

Answer 1

As can be seen from json you are getting object as a source and in your model you create a map to store source but when source is null then you are trying to assign String value to it. That’s why you are getting error.
Try To assign map like:
source = parsedJson['source']== null
? {"id": 0, "name": "Unknown Source"}
: parsedJson['source'],

Answer 2

By this error:
Error From Bloc =type 'String' is not a subtype of type Map
It is seems that the value provided in the NewsModel.fromJson() is a string and not a Map.
You need to do this:
NewsModel.fromJson(json.decode(STRING_FROM_API_RESPONSE))
Note that json is from import 'dart:convert';