CODEWITHSUNDEEP
firebasedictionaryflutterfirebase-realtime-database
Gianluca Bettega
Gianluca Bettega

Reputation: 342

Read list of items from firebase database flutter

I'm trying to build a list of items from this database:

enter image description here

but i'm getting this error:

_TypeError (type 'List<dynamic>' is not a subtype of type 'List<DataSnapshot>')

i can get the item values just using snap2.value but i need to get the element key because it's my item id, to build my list.

import 'package:firebase_database/firebase_database.dart';
final DatabaseReference _refdata =
    FirebaseDatabase.instance.reference().child('host');

getItems() async {
  String _refOnline;
  await _refdata.child("ref").once().then((value) => _refOnline = value.value);
  if (dataRef != _refOnline) {
    await _refdata.child("values/valores").once().then((DataSnapshot snap2) {
  List<DataSnapshot> result = snap2.value;
  lista = result
      .map((element) => Item(
          element.key,
          element.value["nome"],
          element.value["preco"].toDouble(),
          element.value["precoantes"] ?? "",
          element.value["tipo"],
          element.value["disponivel"],
          element.value["descricao"],
          element.value["calorias"]))
      .toList();
});

edit:

with this change im able to return values:

List<Map<dynamic, dynamic>> result =
          List<Map<dynamic, dynamic>>.from(snap2.value);
      result.forEach((element) {
        if (element != null) {
          print(element);
        }
      });

but i cant return the keys (1,2,3,4,5)

and it's the same as doing this(suposing query ordered by keys):

List<dynamic> result = snap2.value;
      int _i = 1;
      result.forEach((value) {
        if (value != null) {
          lista.add(Item(
              _i.toString(),
              value["nome"],
              value["preco"].toDouble(),
              value["precoantes"] ?? "",
              value["tipo"],
              value["disponivel"],
              value["descricao"],
              value["calorias"]));
          _i += 1;
          print(value["nome"]);
          print(value);
          print(lista.length);
        }

and now im getting this error:

NoSuchMethodError (NoSuchMethodError: The method 'add' was called on null.
Receiver: null
Tried calling: add(Instance of 'Item'))

Upvotes: 2

Views: 5186

Answers (2)

Gianluca Bettega
Gianluca Bettega

Reputation: 342

I've managed to solve it using this implementation:

getItems() async {
  String _refOnline;
  List<dynamic> result;
  await _refdata.child("ref").once().then((value) => _refOnline = value.value);
  if (dataRef != _refOnline) {
    await _refdata.child("values/valores").once().then((DataSnapshot snap2) {
      result = snap2.value;
      int _i = 1;
      result.forEach((value) {
        if (value != null) {
          Item _a = Item(
              _i.toString(),
              value["nome"],
              value["preco"].toDouble(),
              value["precoantes"] ?? "",
              value["tipo"],
              value["disponivel"],
              value["descricao"],
              value["calorias"]);
          lista.add(_a);
          _i += 1;
        }
      });
      savepref("ref_key", _refOnline);
    });
  } else {
    lista = [oi, oi2, oi3, oi4, oi5, oi6, oi7, oi8, oi9, oi10, oi11, oi12];
    //readIt();
  }
}

there was a problem on lista definition blocking it to receive new items in lista.add function.

I've now defined lista as:

List<Item> lista = [];

And with the above function, everything now works.

thx Frank van Puffelen !

Upvotes: 0

Frank van Puffelen
Frank van Puffelen

Reputation: 598901

There is no way in FlutterFire to get the child nodes as a list of DataSnapshot objects.

The closest I got was:

currentRoundListener = dbRoot.child('rounds/$currentRoundKey').once.then((snapshot) {
  currentRound = List<String>.from(snapshot.value as List<dynamic>);
});

You could give this a try with:

List<DataSnapshot> result = List<DataSnashot>.from(snap2.value as List<dynamic>);

But more likely the values under the snapshot will only be available as a map:

Map<String, dynamic> result = Map<String, dynamic>.from(snap2.value as Map<dynamic, dynamic>);

If you need to maintain the order of the child nodes, have a look here: Flutter: Firebase Real-Time database orderByChild has no impact on query result and here: Flutter Firebase Database wrong timestamp order

Upvotes: 3

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