将数据从另一个类传递到另一个类 onPressed Flutter
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【中文标题】将数据从另一个类传递到另一个类 onPressed Flutter【英文标题】：Passing data from another class to another's class onPressed Flutter 【发布时间】：2020-07-17 05:03:54 【问题描述】：我正在尝试将数据从 A 类传递到另一个 B 类。B 类会接受它并通过 onPressed（在 B 类中）将数据传递到屏幕 C。
以下是我如何传递和检索数据。目前，我在屏幕 C 中的输出为“null”，它应该显示来自 A 类的数据
从 A 类传递数据class SelectAccount extends StatefulWidget
@override
_SelectAccountState createState() => _SelectAccountState();
class _SelectAccountState extends State<SelectAccount>
var dropdownValue = 'one';
@override
Widget build(BuildContext context)
return Container(
child: Padding(
padding: EdgeInsets.only(right: 10, left: 10),
child: Container(
constraints: BoxConstraints.expand(width: 375.0, height: 100.0),
decoration: BoxDecoration(
color: Colors.white,
border: Border.all(color: Colors.grey),
borderRadius: BorderRadius.circular(5.0),
),
child: Container(
child: Padding(
padding: const EdgeInsets.only(
right: 12.0, left: 12.0, top: 5.0, bottom: 5.0),
child: DropdownButtonHideUnderline(
child: DropdownButton<String>(
itemHeight: 120,
isExpanded: true,
value: dropdownValue,
onChanged: (String value)
setState(()
dropdownValue = value;
);
,
items: [
DropdownMenuItem<String>(
child: Column(
children: <Widget>[
Card(
//margin: EdgeInsets.symmetric(vertical: 20.0, horizontal: 20.0),
child: Container(
padding: EdgeInsets.only(left: 10.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(
'Saving Account',
style: TextStyle(
fontSize: 15.0,
fontWeight: FontWeight.bold,
color: Colors.black,
),
),
SizedBox(
height: 5.0,
),
Text(
'Savings XXX-X-XX563-9',
style: TextStyle(
fontSize: 10.0,
color: Colors.grey[900],
),
),
SizedBox(
height: 15.0,
),
Container(
child: Row(
children: <Widget>[
RichText(
text: TextSpan(
text: '56,302.56',
style: TextStyle(
fontSize: 25.0,
fontWeight: FontWeight.bold,
color: Colors.black,
),
children: <TextSpan>[
TextSpan(
text: ' THB',
style: TextStyle(
fontSize: 15.0,
fontWeight:
FontWeight.bold),
),
],
),
),
],
),
),
],
),
),
),
],
),
value: 'one',
),
DropdownMenuItem<String>(
child: Column(
children: <Widget>[
Card(
//margin: EdgeInsets.symmetric(vertical: 20.0, horizontal: 20.0),
child: Container(
padding: EdgeInsets.only(left: 10.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(
'Saving Account 2',
style: TextStyle(
fontSize: 15.0,
fontWeight: FontWeight.bold,
color: Colors.black,
),
),
SizedBox(
height: 5.0,
),
Text(
'Savings XXX-X-XX563-9',
style: TextStyle(
fontSize: 10.0,
color: Colors.grey[900],
),
),
SizedBox(
height: 15.0,
),
Container(
child: Row(
children: <Widget>[
RichText(
text: TextSpan(
text: '89,302.56',
style: TextStyle(
fontSize: 25.0,
fontWeight: FontWeight.bold,
color: Colors.black,
),
children: <TextSpan>[
TextSpan(
text: ' THB',
style: TextStyle(
fontSize: 15.0,
fontWeight:
FontWeight.bold),
),
],
),
),
],
),
),
],
),
),
),
],
),
value: 'two',
),
//DropdownMenuItem<String>(),
],
),
),
),
),
),
),
);
class PassAccount
static String dropdownValue;
class ToContainer extends StatefulWidget
final PassAccount dropdownValue;
ToContainer(Key key, this.dropdownValue) : super(key: key);
@override
_ToContainerState createState() => _ToContainerState();
class _ToContainerState extends State<ToContainer>
var AccountSelected = PassAccount.dropdownValue;
@override
Widget build(BuildContext context)
return Container(
color: Colors.white,
child: Column(
children: <Widget>[
Container(
padding: EdgeInsets.only(
top: 5.0, left: 10.0, right: 10.0, bottom: 10.0),
child: SafeArea(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Row(
children: <Widget>[
Expanded(
child: CupertinoButton(
child: Text(
'Next',
style: style.clickButton,
),
onPressed: ()
var route = new MaterialPageRoute(
builder: (BuildContext context) =>
new DirectedScreen(
value: PassData(
account: AccountSelected,
)),
);
Navigator.of(context).push(route);
,
color: Colors.blue[600],
borderRadius: BorderRadius.circular(200.0),
disabledColor: Colors.grey,
),
),
],
),
],
),
),
),
],
),
);
class PassData
final String account;
const PassData(
this.account
);
class DirectedScreen extends StatefulWidget
final PassData value;
DirectedScreen(Key key, this.value) : super(key: key);
@override
_DirectedScreenState createState() => _DirectedScreenState();
class _DirectedScreenState extends State<DirectedScreen>
@override
Widget build(BuildContext context)
return Scaffold(
backgroundColor: Colors.white,
appBar: AppBar(
title: Text('Transfer Summary'),
),
body: Container(
child: new Center(
child: Column(
children: <Widget>[
Padding(
child: new Text(
'PASSED VALUES',
style: new TextStyle(
fontWeight: FontWeight.bold, fontSize: 20.0),
textAlign: TextAlign.center,
),
padding: EdgeInsets.only(bottom: 20.0),
),
Padding(
child: new Text(
'Bank : $widget.value.account',
style: new TextStyle(fontWeight: FontWeight.bold),
textAlign: TextAlign.left,
),
padding: EdgeInsets.all(10.0),
),
],
),
),
),
);
感谢您的帮助！
【问题讨论】：
因为dropdownvalue 没有设置？
@BillionShiferaw 实际上是这样。 dropdownValue 是从下拉菜单中选择的项目的值。我已经编辑了上面的代码。
【参考方案1】：
您应该能够使用arguments 将数据从 B 传递到屏幕 C。您可以查看指南以获取示例。
【讨论】：
【参考方案2】：不要为每个小部件创建单独的数据类。而是仅使用现有的。使用widget.dropdownValue 使用状态类中的参数，该参数在有状态小部件类中定义。见以下代码：
onPressed: ()
var route = new MaterialPageRoute(
builder: (BuildContext context) =>
new DirectedScreen(value: widget.dropdownValue),
);
Navigator.of(context).push(route);
,
并且在 DirectedScreen 中使用 PassAccount 仅捕获值。
【讨论】：
感谢您的回复。我正在使用一个单独的类，因为“dropdownValue”的值来自下拉菜单项。代码很长，所以我把它分开了。您认为按照您的建议将它们编译成一个类更好吗？ 是的，最好将所有数据类分开并尽可能重用每个类【参考方案3】：您可以在下面复制粘贴运行完整代码
您需要将var AccountSelected = PassAccount.dropdownValue; 移动到build
代码 sn-p
@override
Widget build(BuildContext context)
var AccountSelected = PassAccount.dropdownValue;
return Container(
工作演示，初始化为 456，点击浮动操作按钮后变为 789
完整代码
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
class PassAccount
static String dropdownValue;
class ToContainer extends StatefulWidget
final PassAccount dropdownValue;
ToContainer(Key key, this.dropdownValue) : super(key: key);
@override
_ToContainerState createState() => _ToContainerState();
class _ToContainerState extends State<ToContainer>
//var AccountSelected = PassAccount.dropdownValue;
@override
Widget build(BuildContext context)
var AccountSelected = PassAccount.dropdownValue;
return Container(
color: Colors.white,
child: Column(
children: <Widget>[
Container(
padding: EdgeInsets.only(
top: 5.0, left: 10.0, right: 10.0, bottom: 10.0),
child: SafeArea(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Row(
children: <Widget>[
Expanded(
child: CupertinoButton(
child: Text(
'Next',
//style: style.clickButton,
),
onPressed: ()
var route = new MaterialPageRoute(
builder: (BuildContext context) =>
new DirectedScreen(
value: PassData(
account: AccountSelected,
)),
);
Navigator.of(context).push(route);
,
color: Colors.blue[600],
borderRadius: BorderRadius.circular(200.0),
disabledColor: Colors.grey,
),
),
],
),
],
),
),
),
],
),
);
class PassData
final String account;
const PassData(this.account);
class DirectedScreen extends StatefulWidget
final PassData value;
DirectedScreen(Key key, this.value) : super(key: key);
@override
_DirectedScreenState createState() => _DirectedScreenState();
class _DirectedScreenState extends State<DirectedScreen>
@override
Widget build(BuildContext context)
return Scaffold(
backgroundColor: Colors.white,
appBar: AppBar(
title: Text('Transfer Summary'),
),
body: Container(
child: new Center(
child: Column(
children: <Widget>[
Padding(
child: new Text(
'PASSED VALUES',
style: new TextStyle(
fontWeight: FontWeight.bold, fontSize: 20.0),
textAlign: TextAlign.center,
),
padding: EdgeInsets.only(bottom: 20.0),
),
Padding(
child: new Text(
'Bank : $widget.value.account',
style: new TextStyle(fontWeight: FontWeight.bold),
textAlign: TextAlign.left,
),
padding: EdgeInsets.all(10.0),
),
],
),
),
),
);
void main()
runApp(MyApp());
class MyApp extends StatelessWidget
@override
Widget build(BuildContext context)
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
class MyHomePage extends StatefulWidget
MyHomePage(Key key, this.title) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
class _MyHomePageState extends State<MyHomePage>
int _counter = 0;
@override
void initState()
PassAccount.dropdownValue = "456";
super.initState();
void _incrementCounter()
PassAccount.dropdownValue = "789";
setState(()
_counter++;
);
@override
Widget build(BuildContext context)
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
ToContainer(),
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
【讨论】：
感谢您的回复。根据您的代码，银行的价值是硬编码的，对。我的 dropdownValue 实际上是下拉菜单项中的值。你认为我仍然可以解决代码吗？谢谢！ 它可以正常工作。获得下拉值后。只需设置 PassAccount.dropdownValue = "yourvalue"。就像单击浮动操作按钮并更改值一样。 AccountSelected 是您原始代码中的固定值。 其实不需要AccountSelected。你可以直接使用 DirectedScreen(value: PassData(account: PassAccount.dropdownValue 我可以知道为什么我不需要 AccountSelected 吗？因为，点击按钮时会传递 dropdownValue。以上是关于将数据从另一个类传递到另一个类 onPressed Flutter的主要内容，如果未能解决你的问题，请参考以下文章