如何将List传递给另一个类

Question

我在这个文件中有一个名为check_symptoms的列表。该列表名为_chosenItems我希望它传递给另一个文件，这是一个有状态的小部件这是我的Check_symptoms.dart代码

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]),
),
],
),
);
}
}

这是我在results。dart

中接收列表的方式

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();
}
}

results.dart的这行代码

State<Results> createState() => _ResultsState(list);

是说:

列表列表类型:列表包:diagnose_app/results.dart

不要在createState中添加任何逻辑。dartno_logic_in_create_state太许多位置参数:0期望，但1发现。试着去掉额外的参数。

我是否以错误的方式传递列表?谢谢你的帮助。

Answer 1

首先，State的实例可以通过widget属性访问其父StatefulWidget的成员。

所以你的问题可以简单地通过访问widget.list来解决，你不需要显式地将列表传递给_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();
}
}

但是，如果您确实希望显式地将值传递给类构造函数，则需要将字段作为成员添加到类中，并定义接受该值的构造函数。