local JSON results are not shwoing - Flutter - json

Question

I have a local JSON file that contains a list of words and I want to display the words in a list using flutter/Dart, for some reason the results are not displayed. All I get is a blank page along with this exception:
The following NoSuchMethodError was thrown building FutureBuilder(dirty, state:
I/flutter (25570): _FutureBuilderState#b10bc):
This is the code I am working with:
class _ListContentState extends State<ListContent> {
List<WordsDictionary> _words = List<WordsDictionary>();
Future<List<WordsDictionary>> _getWords() async{
var dictionaryData = await
DefaultAssetBundle.of(context).loadString('assets/json/dictionary.json');
var words = List<WordsDictionary>();
if(dictionaryData != null){
var jsonData = json.decode(dictionaryData);
for(var word in jsonData){
words.add(WordsDictionary.fromJson(word));
}
}else {
print('fail');
}
return words;
}
#override
void initState(){
_getWords().then((value) {
setState(() {
_words.addAll(value);
});
});
super.initState();
}
#override
Widget build(BuildContext context) {
return ListView.builder(
itemBuilder: (context, index) {
return Card(
elevation: 6.0,
child: Padding(
padding: const EdgeInsets.only(top: 6.0, bottom: 6.0, left: 8.0, right: 8.0),
child: Row(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(_words[index].wordEnglish,),
Spacer(),
Text(_words[index].wordGerman,),
],
),
),
);
},
itemCount: _words.length,
);
}
}
WordDictionary.dart :
class WordsDictionary {
int wordId;
String wordEnglish;
String wordGerman;
WordsDictionary(
this.wordId,
this.wordEnglish,
this.wordGerman
);
WordsDictionary.fromJson(Map<String, dynamic> json){
wordId = json['wordId'];
wordEnglish = json['englishWord'];
wordGerman = json['germanWord'];
}
}

Answer 1

Please wrap your list view with future builder
I slightly change your WordsDictionary class
example json
[
{
"wordId" : "1",
"wordEnglish" : "abc",
"wordGerman" : "def"
},
{
"wordId" : "2",
"wordEnglish" : "123",
"wordGerman" : "456"
}
]
the following is full working code
import 'package:flutter/material.dart';
import 'dart:convert';
void main() => runApp(MyApp());
// To parse this JSON data, do
//
// final wordsDictionary = wordsDictionaryFromJson(jsonString);
List<WordsDictionary> wordsDictionaryFromJson(String str) =>
List<WordsDictionary>.from(
json.decode(str).map((x) => WordsDictionary.fromJson(x)));
String wordsDictionaryToJson(List<WordsDictionary> data) =>
json.encode(List<dynamic>.from(data.map((x) => x.toJson())));
class WordsDictionary {
String wordId;
String wordEnglish;
String wordGerman;
WordsDictionary({
this.wordId,
this.wordEnglish,
this.wordGerman,
});
factory WordsDictionary.fromJson(Map<String, dynamic> json) =>
WordsDictionary(
wordId: json["wordId"],
wordEnglish: json["wordEnglish"],
wordGerman: json["wordGerman"],
);
Map<String, dynamic> toJson() => {
"wordId": wordId,
"wordEnglish": wordEnglish,
"wordGerman": wordGerman,
};
}
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
// This is the theme of your application.
//
// Try running your application with "flutter run". You'll see the
// application has a blue toolbar. Then, without quitting the app, try
// changing the primarySwatch below to Colors.green and then invoke
// "hot reload" (press "r" in the console where you ran "flutter run",
// or simply save your changes to "hot reload" in a Flutter IDE).
// Notice that the counter didn't reset back to zero; the application
// is not restarted.
primarySwatch: Colors.blue,
),
home: ListContent(),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
// This widget is the home page of your application. It is stateful, meaning
// that it has a State object (defined below) that contains fields that affect
// how it looks.
// This class is the configuration for the state. It holds the values (in this
// case the title) provided by the parent (in this case the App widget) and
// used by the build method of the State. Fields in a Widget subclass are
// always marked "final".
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
// This call to setState tells the Flutter framework that something has
// changed in this State, which causes it to rerun the build method below
// so that the display can reflect the updated values. If we changed
// _counter without calling setState(), then the build method would not be
// called again, and so nothing would appear to happen.
_counter++;
});
}
#override
Widget build(BuildContext context) {
// This method is rerun every time setState is called, for instance as done
// by the _incrementCounter method above.
//
// The Flutter framework has been optimized to make rerunning build methods
// fast, so that you can just rebuild anything that needs updating rather
// than having to individually change instances of widgets.
return Scaffold(
appBar: AppBar(
// Here we take the value from the MyHomePage object that was created by
// the App.build method, and use it to set our appbar title.
title: Text(widget.title),
),
body: Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: Column(
// Column is also a layout widget. It takes a list of children and
// arranges them vertically. By default, it sizes itself to fit its
// children horizontally, and tries to be as tall as its parent.
//
// Invoke "debug painting" (press "p" in the console, choose the
// "Toggle Debug Paint" action from the Flutter Inspector in Android
// Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
// to see the wireframe for each widget.
//
// Column has various properties to control how it sizes itself and
// how it positions its children. Here we use mainAxisAlignment to
// center the children vertically; the main axis here is the vertical
// axis because Columns are vertical (the cross axis would be
// horizontal).
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
class ListContent extends StatefulWidget {
#override
_ListContentState createState() => _ListContentState();
}
class _ListContentState extends State<ListContent> {
List<WordsDictionary> _words = List<WordsDictionary>();
Future<List<WordsDictionary>> _getWords() async {
var dictionaryData = await DefaultAssetBundle.of(context)
.loadString('assets/json/dictionary.json');
var words = List<WordsDictionary>();
if (dictionaryData != null) {
words = wordsDictionaryFromJson(dictionaryData);
print("words lenght ${words.length}");
} else {
print('fail');
}
return words;
}
#override
Widget build(BuildContext context) {
return FutureBuilder(
builder: (context, AsyncSnapshot<List<WordsDictionary>> wordSnap) {
switch (wordSnap.connectionState) {
case ConnectionState.none:
return new Text('none');
case ConnectionState.waiting:
return new Center(child: new CircularProgressIndicator());
case ConnectionState.active:
return new Text('');
case ConnectionState.done:
if (wordSnap.hasError) {
return new Text(
'${wordSnap.error}',
style: TextStyle(color: Colors.red),
);
} else {
return ListView.builder(
itemCount: wordSnap.data.length,
itemBuilder: (context, index) {
WordsDictionary wordsDictionary = wordSnap.data[index];
return Card(
elevation: 6.0,
child: Padding(
padding: const EdgeInsets.only(
top: 6.0, bottom: 6.0, left: 8.0, right: 8.0),
child: Row(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(
wordsDictionary.wordEnglish,
),
Spacer(),
Text(
wordsDictionary.wordGerman,
),
],
),
));
});
}
}
},
future: _getWords(),
);
}
}