制作新小部件后清除类的列表
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【中文标题】制作新小部件后清除类的列表【英文标题】:List for a class clears out after making new widget 【发布时间】:2020-09-27 19:40:50 【问题描述】:我正在尝试学习颤振,但我偶然发现了一个我无法解决的问题。我有一个 MyApp/MyAppState 类,它有一个小部件列表(ovelser),在 listVeiw.builder 中使用。
import './barbutton.dart';
import './ovelser.dart';
void main()
runApp(MaterialApp(home: MyApp()));
class MyApp extends StatefulWidget
// This widget is the root of your application.
@override
State<StatefulWidget> createState()
// TODO: implement createState
return MyAppState();
class MyAppState extends State<MyApp>
List<Widget> ovelser = [];
@override
Widget build(BuildContext context)
return Scaffold(
appBar: AppBar(
title: Text("progresjon"),
backgroundColor: Colors.blue,
actions: <Widget>[AddButton(nameOvelse)],
),
body: ListView.builder(
itemCount: ovelser.length,
itemBuilder: (context, index)
final Widget ovelse = ovelser[index]; // lagrer bare ovelse objektet
return Dismissible(
// dismissible gjør det mulig å slette ting i listView
key: UniqueKey(),
onDismissed: (direction)
//hva som skjer når man skal slette
setState(()
ovelser.removeAt(index);
);
,
background: Container(
color: Colors.red,
),
//child er hva som skal være objektet som kan slettes
child: ovelse,
);
,
),
);
void addOvelse(String name)
setState(()
ovelser.add(Ovelser(name));
);
print(ovelser.length);
nameOvelse(BuildContext context)
TextEditingController custumcontroller = TextEditingController();
return showDialog(
context: context,
builder: (BuildContext context)
return AlertDialog(
title: Text("new activity"),
content: TextField(
controller: custumcontroller,
),
actions: <Widget>[
FlatButton(
child: Text("create"),
onPressed: ()
String activityName = " " + custumcontroller.text;
addOvelse(activityName);
Navigator.of(context).pop();
,
)
],
);
,
);
列表 ovelser 接受 Ovelser 对象。这些对象有一个类,它有一个接收整数的列表(progresjonsList),我可以通过 AlertDialog 添加到该列表中。 int 中带有 progresjonList 的类的代码:
import './ovleseraddbutton.dart';
class Ovelser extends StatefulWidget
final String name;
Ovelser(this.name);
@override
OvelserState createState() => OvelserState();
class OvelserState extends State<Ovelser>
List<int> progresjonList = [];
@override
Widget build(BuildContext context)
return Container(
height: 80,
width: double.infinity,
alignment: Alignment.centerLeft,
decoration: BoxDecoration(
border: Border(
top: BorderSide(width: 0.5, color: Colors.grey),
bottom: BorderSide(width: 0.5, color: Colors.grey),
)),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Flexible(
child: Container(
child: Text(widget.name,
overflow: TextOverflow.fade,
softWrap: false,
maxLines: 1,
style: TextStyle(
fontStyle: FontStyle.italic,
fontSize: 20,
fontWeight: FontWeight.bold)),
)),
OvelserAddbutton(addvalue)
]),
);
void insertValue(int value)
setState(()
this.progresjonList.add(value);
);
addvalue(BuildContext context)
TextEditingController custumcontroller = TextEditingController();
return showDialog(
context: context,
builder: (BuildContext context)
return AlertDialog(
title: Text("add new value"),
content: TextField(
controller: custumcontroller,
keyboardType: TextInputType.number,
),
actions: <Widget>[
FlatButton(
child: Text("add"),
onPressed: ()
String stringnumber = custumcontroller.text;
int number = int.parse(stringnumber);
insertValue(number);
print(number);
print(progresjonList.length);
print(this.progresjonList);
Navigator.of(context).pop();
,
)
],
);
,
);
问题是每次我在 ovelser(ListView 中使用的列表)中创建一个新小部件时,带有整数的列表 (progresjonList) 都会被清除,因此它们是空的,并且不会保留先前由 AlertDialog 添加的值。我不明白我怎么能防止这种情况发生,所以我保持整数相加。谁能帮我?提前谢谢你:)
还有两个其他小文件,其中只有图标小部件,我认为这不是问题,但如果您需要它们,它们就是:)
class AddButton extends StatelessWidget
final Function setInFunction;
AddButton(this.setInFunction);
@override
Widget build(BuildContext context)
return IconButton(
icon: Icon(Icons.add),
onPressed: () => setInFunction(context),
);
import 'package:flutter/material.dart';
class OvelserAddbutton extends StatelessWidget
final Function setInFunction;
OvelserAddbutton(this.setInFunction);
@override
Widget build(BuildContext context)
return IconButton(
icon: Icon(Icons.add),
onPressed: () => setInFunction(context),
);
```
【问题讨论】:
【参考方案1】:progessjonList 对于 Ovelser 类是本地的。您需要将 overserList 传递给 Ovelser 类。
class Ovelser extends StatefulWidget
final String name;
final List<int> list;
Ovelser(this.name, this.list);
@override
OvelserState createState() => OvelserState();
然后,当您想添加到 OvelserState 中的列表时,只需使用
widget.list.add(/*add int here*/);
我看到的是你的 insertValue 函数
void insertValue(int value)
setState(()
widget.list.add(value);
);
您传入的列表将是对原始类中的 ovelser 列表的引用。
【讨论】:
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