Dart 颤振状态类
新的颤振和一般新的编程 目标:我试图创建一个有状态的文本字段,我可以从main调用它(传递字段名称和字段限制)。基本上,我试图简洁,减少连续文本字段的代码量 我主要有以下代码:Dart 颤振状态类,dart,flutter,Dart,Flutter,新的颤振和一般新的编程 目标:我试图创建一个有状态的文本字段,我可以从main调用它(传递字段名称和字段限制)。基本上,我试图简洁,减少连续文本字段的代码量 我主要有以下代码: import 'package:flutter/material.dart'; import 'package:ui_practice2/StatefulForm.dart'; void main() => runApp(new KangarooApp()); class KangarooApp extends
import 'package:flutter/material.dart';
import 'package:ui_practice2/StatefulForm.dart';
void main() => runApp(new KangarooApp());
class KangarooApp extends StatelessWidget {
Widget build(BuildContext context){
return new MaterialApp(
home: MyStateful(),
);
}
}
class MyStateful extends StatefulWidget {
MyStateful({Key key, this.title}): super(key: key);
final String title;
@override
MyState createState() => new MyState();
}
class MyState extends State<MyStateful> {
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text("Assets")
),
body: new Container(
margin: new EdgeInsets.symmetric(vertical: 20.0, horizontal: 20.0),
child: new ListView(
children: <Widget>[
new StatefulForm("Peter", 10)
],
)
)
);
}
}
导入“包装:颤振/材料.省道”;
导入“package:ui_practice2/StatefulForm.dart”;
void main()=>runApp(新袋鼠app());
类KangarooApp扩展了无状态小部件{
小部件构建(构建上下文){
返回新材料PP(
主页:MyStateful(),
);
}
}
类MyStateful扩展StatefulWidget{
MyStateful({Key,this.title}):super(Key:Key);
最后的字符串标题;
@凌驾
MyState createState()=>新建MyState();
}
类MyState扩展状态{
@凌驾
小部件构建(构建上下文){
归还新脚手架(
appBar:新的appBar(
标题:新文本(“资产”)
),
主体:新容器(
边距:新边集。对称(垂直:20.0,水平:20.0),
子:新列表视图(
儿童:[
新的州政府形式(“彼得”,10岁)
],
)
)
);
}
}
上面的目标是通过传入StatefulForm.dart中的两个参数来调用StatefulForm类,如下所示:
import 'package:flutter/material.dart';
import 'package:ui_practice2/main.dart';
class StatefulForm extends State<MyStateful> {
final TextEditingController _texteditcontrol = new TextEditingController();
String fieldName = "";
int maxLength = 0;
@override
StatefulForm(String text, int limitNum){
fieldName= text;
maxLength = limitNum;
}
Widget build(BuildContext context) {
final theme = Theme.of(context);
return new Theme(
data: theme.copyWith(primaryColor: Color.fromRGBO(33, 206, 153, 1.0)),
child: new TextField(
maxLength: maxLength,
controller: _texteditcontrol,
decoration: new InputDecoration(
labelText: fieldName),
onChanged: (String e) {
setState (() {
fieldName = e;
});
},
)
);
}
}
导入“包装:颤振/材料.省道”;
导入“包:ui_practice2/main.dart”;
类StatefulForm扩展状态{
final TextEditingController_TextEditingControl=新的TextEditingController();
字符串fieldName=“”;
int maxLength=0;
@凌驾
StatefulForm(字符串文本,int limitNum){
字段名=文本;
maxLength=limitNum;
}
小部件构建(构建上下文){
最终主题=主题(上下文);
返回新主题(
数据:theme.copyWith(primaryColor:Color.fromRGBO(332061531.0)),
孩子:新文本字段(
maxLength:maxLength,
控制器:_texteditcontrol,
装饰:新的输入装饰(
labelText:fieldName),
一旦更改:(字符串e){
设置状态(){
fieldName=e;
});
},
)
);
}
}
当我调用StatefulForm(“Peter”,10)时,我得到了主要的红线错误,即:“元素类型StatefulForm不能分配给列表类型小部件”
有人对此有什么建议吗?甚至有可能创建一个可以重复调用的有状态资产吗?我不想在这里写一个读文档的答案,但我真的认为读文档是一个好主意,因为它可能比我更好地解释
至少,试着在颤振页面上完成这一步,然后
用我自己的话来说是TLDR。我对基本的颤振模板做了一些修改,用一个无状态小部件来说明这一点
import 'package:flutter/material.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new 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 press Run > Flutter Hot Reload in IntelliJ). Notice that the
// counter didn't reset back to zero; the application is not restarted.
primarySwatch: Colors.blue,
),
home: new MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, 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
_MyHomePageState createState() => new _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 new Scaffold(
appBar: new 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: new Text(widget.title),
),
body: new Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: new Column(
// Column is also 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 paint" (press "p" in the console where you ran
// "flutter run", or select "Toggle Debug Paint" from the Flutter tool
// window in IntelliJ) 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>[
new Text(
'You have pushed the button this many times:',
),
new TimesPressedDisplay(numTimesPressed: _counter);
],
),
),
floatingActionButton: new FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: new Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
class TimesPressedDisplay extends StatelessWidget {
final int numTimesPressed;
TimesPressedDisplay({@required this.numTimesPressed}):
assert(numTimesPressed != null);
@override
Widget build(BuildContext context) {
return new Text(
'$numTimesPressed',
style: Theme.of(context).textTheme.display1,
),
}
}
导入“包装:颤振/材料.省道”;
void main()=>runApp(新的MyApp());
类MyApp扩展了无状态小部件{
//此小部件是应用程序的根。
@凌驾
小部件构建(构建上下文){
返回新材料PP(
标题:“颤振演示”,
主题:新主题数据(
//这是应用程序的主题。
//
//尝试使用“flutter run”运行应用程序。您将看到
//应用程序有一个蓝色工具栏。然后,在不退出应用程序的情况下,重试
//将下面的primarySwatch更改为Colors.green,然后调用
//“热重新加载”(在运行“颤振运行”的控制台中按“r”,
//或者在IntelliJ中按Run>Flatter Hot Reload)。请注意
//计数器未重置回零;应用程序未重新启动。
主样本:颜色。蓝色,
),
主页:新MyHomePage(标题:“颤振演示主页”),
);
}
}
类MyHomePage扩展StatefulWidget{
MyHomePage({Key,this.title}):超级(Key:Key);
//此小部件是应用程序的主页。它是有状态的,表示
//它有一个状态对象(定义如下),其中包含影响
//看起来怎么样。
//此类是状态的配置。它保存值(在此
//案例名称)由家长(在本例中为应用程序小部件)提供,以及
//由State的build方法使用。小部件子类中的字段包括
//始终标记为“最终”。
最后的字符串标题;
@凌驾
_MyHomePageState createState()=>new_MyHomePageState();
}
类_MyHomePageState扩展状态{
int _计数器=0;
void _incrementCounter(){
设置状态(){
//这个对setState的调用告诉颤振框架,某些东西
//已在此状态下更改,这将导致它重新运行下面的生成方法
//以便显示能够反映更新的值。如果我们更改
//_计数器,而不调用setState(),则生成方法将不可用
//再打一次电话,似乎什么也没发生。
_计数器++;
});
}
@凌驾
小部件构建(构建上下文){
//每次调用setState时都会重新运行此方法,例如,按done
//通过上面的_incrementCounter方法。
//
//对颤振框架进行了优化,以制定重新运行的构建方法
//快速,这样你就可以重建任何需要更新的东西
//而不是必须单独更改小部件的实例。
归还新脚手架(
appBar:新的appBar(
//在这里,我们从MyHomePage对象中获取由创建的值
//使用App.build方法,并使用它设置appbar标题。
标题:新文本(widget.title),
),
正文:新中心(
//中心是一个布局小部件。它接受一个子元素并对其进行定位
/在父母的中间。
子:新列(
//列也是一个布局小部件,它包含一系列子项和
//安排他们