我正在做一辆手推车。但是，我遇到了一个问题。按照计划，用户可以添加购物车中的商品数量。但是，由于我使用了一个变量，计数器会同时在各处增加/减少。如何修复？附言：我不知道这个产品会有多少，它是用户自己添加的
这是我的代码-保存状态-
int value = 1;
inc() {
setState(() {
value++;
});
}
dec() {
setState(() {
value--;
});
}
-扩展(
child: ListView.builder(
controller: controller,
padding: EdgeInsets.all(5),
itemCount: HomeBody.shoppingBasketHeader!.length,
itemBuilder: (context, index) {
if (index < HomeBody.shoppingBasketHeader!.length) {
return Container(
padding: EdgeInsets.all(5),
margin: EdgeInsets.all(2),
decoration: const BoxDecoration(
border: Border(bottom: BorderSide(color: Colors.black))
),
child: Row(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Column(
children: [
Container(
width: 150,
child: Image.network('http://10.0.2.2:1337${HomeBody.shoppingBasketImage?[index]}'),
)
],
),
Column(
children: [
Container(
width: 200,
child: Column(
children: [
Container(
margin: EdgeInsets.all(5),
child: Text(' ${HomeBody.shoppingBasketHeader?[index]}', style: TextStyle(fontSize: 15),),
),
],
),
),
Container(
width: 200,
child: Column(
children: [
Container(
margin: EdgeInsets.all(5),
child: Text(' ${HomeBody.shoppingBasketPrice?[index]}', style: TextStyle(fontSize: 15),),
),
],
),
),
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Container(
child: IconButton(onPressed: () {inc();}, icon: Icon(Icons.add)),
),
Container(
child: Text('$value'),
),
Container(
child: IconButton(onPressed: () {dec();}, icon: Icon(Icons.remove)),
)
],
)
],
),
],
),
);
} else {
return Padding(padding: EdgeInsets.symmetric(
vertical: 10),
child: Center(
child: Text('Список полностью загружен!'),
),
);
}
}
)
**
- 选项1
**
为下面的代码段创建一个单独的小部件，并在本地声明计数变量(值(。
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Container(
child: IconButton(onPressed: () {inc();}, icon: Icon(Icons.add)),
),
Container(
child: Text('$value'),
),
Container(
child: IconButton(onPressed: () {dec();}, icon: Icon(Icons.remove)),
)
],
)
**
- 选项2
**为每行数据创建一个单独的类，并使用List
class CartRow{
int数量，双倍价格，串产品，}
**
- 选项3
**使用选项1和选项2 中的新类别/实体
-------------------------选项1代码------------------
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
class ShoppingCartLine extends StatefulWidget {
const ShoppingCartLine({Key? key}) : super(key: key);
@override
_ShoppingCartLineState createState() => _ShoppingCartLineState();
}
class _ShoppingCartLineState extends State<ShoppingCartLine> {
int? value;
@override
void initState() {
super.initState();
value = 1;
}
@override
Widget build(BuildContext context) {
return _getBody();
}
Widget _getBody(){
return Row(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Container(
child: IconButton(onPressed: () {inc();}, icon: Icon(Icons.add)),
),
Container(
child: Text('${value.toString()}'),
),
Container(
child: IconButton(onPressed: () {dec();}, icon: Icon(Icons.remove)),
)
],
);
}
inc() {
setState(() {
value = (value! + 1);
});
}
dec() {
setState(() {
if(value! > 1){
value = (value! - 1);
}
});
}
}
--------------------------------main.dart--------------------------------导入"package:flutter/material.dart"；
import 'features/shopping_cart_line.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
// 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: const MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
const MyHomePage({Key? key, required 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
State<MyHomePage> 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>[
const Text(
'You have pushed the button this many times:',
),
Column(
children: [
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
const ShoppingCartLine(),
const ShoppingCartLine(),
],
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: const Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
enter code here