How can I pass a List to another class - flutter

Question

I have a list in this file called check_symptoms.dart which the list is called _chosenItems
i want it to pass it to another file which is a stateful widget
here's my code for Check_symptoms.dart
import 'package:diagnose_app/results.dart';
import 'package:flutter/material.dart';
import 'dart:convert';
import 'package:flutter/services.dart';
class SymptomsChecker extends StatefulWidget {
const SymptomsChecker({Key? key}) : super(key: key);
#override
State<SymptomsChecker> createState() => _SymptomsCheckerState();
}
class _SymptomsCheckerState extends State<SymptomsChecker> {
List _items = [];
List _itemsForDisplay = [];
List _chosenItems = [];
int maxheight = 0;
ScrollController _scrollController = ScrollController();
Future<void> readJson() async {
final String response =
await rootBundle.loadString('assets/data/Symptoms.json');
final data = await json.decode(response);
setState(() {
_items = data["Symptoms"];
_itemsForDisplay = _items;
});
}
#override
void initState() {
// TODO: implement initState
readJson();
super.initState();
}
#override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: const Color.fromARGB(255, 105, 120, 255),
body: Padding(
padding: const EdgeInsets.all(5),
child: Column(
children: [
// Display the data loaded from sample.json
// _ListChosenItem(23),
SizedBox(
height: 25,
),
_searchBar(),
Divider(
height: 1,
),
Expanded(
child: ListView.builder(
itemBuilder: (context, index) {
return _ListItem(index);
},
itemCount: _itemsForDisplay.length,
),
),
Divider(
height: 2,
),
Padding(
padding: const EdgeInsets.all(3.0),
child: LimitedBox(
maxHeight: 200,
child: Scrollbar(
controller: _scrollController,
child: SingleChildScrollView(
//scrollDirection: Axis.horizontal,
child: Wrap(
children: _chosenItems.map((item) {
//print(_chosenItems);
return chosenItems(item);
}).toList(),
),
),
),
),
),
Divider(
color: Colors.black,
height: 10,
thickness: 1,
),
Padding(
padding: const EdgeInsets.symmetric(horizontal: 10),
child: Container(
height: 50,
width: double.infinity,
child: ElevatedButton(
onPressed: () {
Navigator.of(context).push(MaterialPageRoute(
// sending chosenItems to results.dart
builder: (context) => Results(list: _chosenItems)));
},
child: Text(
"Find Results",
style: TextStyle(fontSize: 20, fontWeight: FontWeight.w500),
),
style: ElevatedButton.styleFrom(),
),
),
),
SizedBox(
height: 5,
),
],
),
),
);
}
Padding chosenItems(item) {
return Padding(
padding: const EdgeInsets.all(3.0),
child: Builder(builder: (context) {
return ElevatedButton.icon(
onPressed: () {
setState(() {
_itemsForDisplay.add(item);
//_items.add(item);
_chosenItems.remove(item);
});
},
style: ElevatedButton.styleFrom(
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(10)),
textStyle:
const TextStyle(fontSize: 15, fontWeight: FontWeight.w400)),
label: Text(item),
icon: Icon(
Icons.remove_circle,
color: Color.fromARGB(255, 255, 217, 216),
),
);
}),
);
}
_searchBar() {
return Padding(
padding: const EdgeInsets.all(8),
child: TextField(
decoration: InputDecoration(
border: OutlineInputBorder(borderRadius: BorderRadius.circular(10)),
filled: true,
fillColor: Color.fromARGB(255, 244, 244, 244),
hintText: 'Search Symptoms'),
style: TextStyle(color: Color.fromARGB(255, 22, 25, 52)),
maxLines: 1,
onChanged: (text) {
text = text.toLowerCase();
setState(() {
_itemsForDisplay = _items.where((item) {
var itemEntity = item.toLowerCase();
return itemEntity.contains(text);
}).toList();
});
},
),
);
}
_ListItem(index) {
return Wrap(
children: [
ElevatedButton(
onPressed: () {
setState(() {
_chosenItems.add(_itemsForDisplay[index]);
_itemsForDisplay.removeAt((index));
//_items.removeAt((index));
});
},
style: ElevatedButton.styleFrom(
textStyle:
const TextStyle(fontSize: 18, fontWeight: FontWeight.w500)),
child: Text(_itemsForDisplay[index]),
),
],
);
}
_ListChosenItem(index) {
return Padding(
padding: const EdgeInsets.all(8.0),
child: Wrap(
children: [
ElevatedButton(
onPressed: () {},
style: ElevatedButton.styleFrom(
textStyle: const TextStyle(fontSize: 20)),
child: Text(_chosenItems[index]),
),
],
),
);
}
}
here's the way I'm receiving the list in results.dart
import 'package:flutter/material.dart';
class Results extends StatefulWidget {
final List list;
const Results({required this.list});
#override
State<Results> createState() => _ResultsState(list);
}
class _ResultsState extends State<Results> {
#override
Widget build(BuildContext context) {
print(list);
return Scaffold();
}
}
this line of code of results.dart
State<Results> createState() => _ResultsState(list);
is says:
List list Type: List
package:diagnose_app/results.dart
Don't put any logic in createState.dartno_logic_in_create_state Too
many positional arguments: 0 expected, but 1 found. Try removing the
extra arguments.
Am I passing the list in a wrong way? thanks for helping in advance.

Answer 1

First of all, an instance of State can access the members of its parent StatefulWidget via the widget property.
So your particular problem can be solved simply by accessing widget.list, you don't need to pass the list explicitly to _ResultsState:
import 'package:flutter/material.dart';
class Results extends StatefulWidget {
final List list;
const Results({required this.list});
#override
State<Results> createState() => _ResultsState();
}
class _ResultsState extends State<Results> {
#override
Widget build(BuildContext context) {
print(widget.list);
return Scaffold();
}
}
But further, if you do want to explicitly pass a value to a class constructor, you'll need to add the field as a member to the class and define the constructor that takes that value.