新文本(counter.toString())显示不更新计数器增量在颤振
新文本(counter.toString())显示不更新计数器增量在颤振
提问于 2019-11-01 11:01:45
我正在使用flutter构建一个食品推车应用程序。但是，当Listtile的尾部增加或减少时，我不得不显示计数器值。
每当一个新的项目被添加到购物车时，计数器就会增加，但是应用程序不会显示当前的计数器值。
下面是下面的代码。我已经在faced.Thank你的问题上发表了评论。
import 'package:flutter/material.dart';
import 'package:ifhe_canteen/StudentCart.dart';
class StudentHomePage extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: HomePage(),
);//MaterialApp
}
}
class HomePage extends StatefulWidget{
@override
HomePage1 createState() => new HomePage1();
}
class HomePage1 extends State<HomePage>{
int selectedPage=0;
final pageOptions=[
Text('Messages'),
Text('Cart'),
Text('Profile'),
];
@override
Widget build(BuildContext context) {
var Listview=ListView(
children: <Widget>[
ListTile(
leading: Icon(Icons.fastfood),
)
],
);
return Scaffold(
appBar: AppBar(
title: Text('Categories'),
),
body:new Container(
child: new ListView.builder(
itemBuilder: (BuildContext context, int index) {
return new StuffInTiles(listOfTiles[index]);
},
itemCount: listOfTiles.length,
),
),//body: pageOptions[selectedPage],
bottomNavigationBar: BottomNavigationBar(
currentIndex: selectedPage,
onTap: (int index){
setState(() {
selectedPage=index;
});
},// this will be set when a newx tab is tapped
items: [
BottomNavigationBarItem(
icon: new Icon(Icons.home),
title: new Text('Home'),
),
BottomNavigationBarItem(
icon: new Icon(Icons.shopping_basket),
title: new Text('Cart'),
),
BottomNavigationBarItem(
icon: Icon(Icons.person),
title: Text('Profile'),
),
],
),
);
}
}
class StuffInTiles extends StatelessWidget {
final MyTile myTile;
StuffInTiles(this.myTile);
int _itemCount;
String item;
void _removeproduct(){
_itemCount--;
print(_itemCount);
}
int _addproduct(){
_itemCount++;
print(_itemCount);
item=_itemCount.toString();
print(item);
return _itemCount;
}
@override
Widget build(BuildContext context) {
return _buildTiles(myTile);
}
Widget _buildTiles (MyTile t) {
if (t.children.isEmpty)
{
return new ListTile(
dense: true,
enabled: true,
isThreeLine: false,
title: new Text(t.title),
trailing:new Row(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
new IconButton(icon: new Icon(Icons.remove),onPressed:()=>_removeproduct()),
new Text(_itemCount.toString()),//here, the incremented value is not displayed
new IconButton(icon: new Icon(Icons.add),onPressed:()=>_addproduct()),//here the function is called
],
),
onTap:()=>print("here cart value will be incremented"),
);
}
return new ExpansionTile(
key: new PageStorageKey<MyTile>(t),
title: new Text(t.title),
children: t.children.map(_buildTiles).toList(),
);
}
}
class MyTile {
String title;
List<MyTile> children;
MyTile(this.title, [this.children = const <MyTile>[]]);
}
List<MyTile> listOfTiles = <MyTile>[
new MyTile(
'Mess 1',
<MyTile>[
new MyTile(
'Maggie',
<MyTile>[
new MyTile('Veg Cheese Maggie'),
new MyTile('Plain Maggie'),
new MyTile('Chicken Maggie'),
],
),//Maggie
new MyTile(
'Paratha',
<MyTile>[
new MyTile('Veg Paratha'),
new MyTile('Veg Butter Paratha'),
new MyTile('Chicken Paratha'),
new MyTile('Chicken Butter Paratha'),
],
),//Paratha
],
),
new MyTile(
'Mess 2',
<MyTile>[
new MyTile(
'Maggie',
<MyTile>[
new MyTile('Veg Cheese Maggie'),
new MyTile('Plain Maggie'),
new MyTile('Chicken Maggie'),
],
),//Maggie
new MyTile(
'Paratha',
<MyTile>[
new MyTile('Veg Paratha'),
new MyTile('Veg Butter Paratha'),
new MyTile('Chicken Paratha'),
new MyTile('Chicken Butter Paratha'),
],
),//Paratha
],
),
];回答 1
Stack Overflow用户
回答已采纳
发布于 2019-11-01 11:33:32
当您更新代码中的变量时，您需要调用setState，并且希望在屏幕上看到这种更改。注意，它只在StatefulWidgets中工作，这意味着如果您需要它，您需要一个StatefulWidget (就像您已经做的那样)。setState方法将刷新屏幕，查看的值将发生变化。
编辑_addproduct和_removeproduct函数，以便在_itemCounter变量上有一个setState：
void _removeproduct(){
setState((){
_itemCount--;
});
}
int _addproduct(){
setState((){
_itemCount++;
});
}我建议你读一些文章如何使用颤振状态。诚挚的问候。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/58658105
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