Ufdjrw

I use flutter with package firebase_database. With the code

final FirebaseDatabase _database = FirebaseDatabase.instance;

@override
void initState() 
 super.initState();
 _newsList = new List();

 _newsQuery = _database
 .reference()
 .child('news')
 .orderByChild('published')
 .limitToFirst(10);

 _newsQuery.onChildAdded.listen(_onEntryAdded);


_onEntryAdded(Event event) 
 setState(() 
 News n = News.fromSnapshot(event.snapshot);
 _newsList.add(n);
 );

i get a perfect list _newsList of all queried items. The news class is

 import 'package:firebase_database/firebase_database.dart';

 class News 
 String key;
 String image;
 String text;
 String title;
 String published;

 News(this.image, this.text, this.published);

 News.fromSnapshot(DataSnapshot snapshot) :
 key = snapshot.key,
 text = snapshot.value["text"],
 title = snapshot.value["title"],
 image = snapshot.value["image"],
 published = snapshot.value["published"];

 toJson() 
 return 
 "image": image,
 "text": text,
 "title": title,
 "published": published,
 ;
 

The json-structure in the database is:

database
|__news
 |__post1
 | |__text: "Lorem ipsum"
 | |__title: "Title of post"
 |
 |__post2
 |__ ...

Now i want to load a nested json-structure from the database with

database
|__news
 |__category1
 | |
 | |__post1
 | | |__text: "Lorem ipsum 1"
 | | |__title: "Title of post1"
 | |__post2
 | | |__text: "Lorem ipsum 2"
 | | |__title: "Title of post2"
 | |__description: "description text"
 | |__id: "id of category"
 | .
 | .
 |
 |__category2
 | |
 | |__post34
 | | |__text: "Lorem ipsum 34"
 | | |__title: "Title of post34"
 | .
 | .

I try to find a solution to load the nested DataSnapshots into class, but i always get exceptions. The best code i tried so far is

 class News {
 final List<Category> categories;

 News(this.categories);

 factory News.fromSnapshot(DataSnapshot snapshot) 

 List<dynamic> listS = snapshot.value;

 listS.forEach((value) =>
 print('V $value')
 );

 List<Category> list = listS.map((i) => Category.fromJson(i)).toList();

 return News(
 categories: list
 );

 

But this throws the exception

E/flutter ( 5882): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: type '_InternalLinkedHashMap' is not a subtype of type 'Map'
E/flutter ( 5882): #0 new News.fromSnapshot. (package:app/models/news.dart:23:55)
E/flutter ( 5882): #1 MappedListIterable.elementAt (dart:_internal/iterable.dart:414:29)
E/flutter ( 5882): #2 ListIterable.toList (dart:_internal/iterable.dart:219:19)

I found in flutter and dart no code-example to load nested json with DataSnapshot. Do you know any code-sample?

If you want to see my full code, then look at https://github.com/matthiaw/gbh_app. The not working part is the nested json in calendar at https://github.com/matthiaw/gbh_app/blob/4de0f20f6162801db86ef6644609829c27a4dd76/lib/models/calendar.dart