Flutter 颤振中的下拉按钮问题
我在使用Flatter(1.0)中的Dropdownbutton小部件时遇到问题,它经常抛出错误 以下是我的代码:Flutter 颤振中的下拉按钮问题,flutter,Flutter,我在使用Flatter(1.0)中的Dropdownbutton小部件时遇到问题,它经常抛出错误 以下是我的代码: import 'package:flutter/material.dart'; void main() => runApp(new Myapp()); class Myapp extends StatefulWidget { @override State<StatefulWidget> createState() { return new M
import 'package:flutter/material.dart';
void main() => runApp(new Myapp());
class Myapp extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return new Myappstate();
}
}
class Myappstate extends State<Myapp> {
String value = '';
List<String> values = [];
void init() {
values.addAll(['one', 'two']);
value = values.elementAt(0);
}
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text("drop down demo"),
),
body: new Container(
child: new Column(
children: <Widget>[
new DropdownButton(
items: values.map((String val) {
return new DropdownMenuItem(
value: val,
child: Text(val),
);
}).toList(),
onChanged: null,
)
],
),
),
);
}
}
我试图添加这个非常基本的小部件,但由于某些原因,我一直无法找到问题
请告知我能找到的任何帮助。您必须包装在MaterialApp中,并在initState中加载初始数据 检查此代码,但有细微更改:
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: MyHomeapp(),
);
}
}
class MyHomeapp extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return new MyHomeappstate();
}
}
class MyHomeappstate extends State<MyHomeapp> {
String value = '';
List<String> values = [];
@override
void initState() {
super.initState();
setState(() {
values.addAll(['one', 'two']);
value = values.elementAt(0);
});
}
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text("drop down demo"),
),
body: new Container(
child: new Column(
children: <Widget>[
new DropdownButton(
hint: Container(
child: Text('Select option'),
),
items: values.map((String val) {
return new DropdownMenuItem(
value: val,
child: Text(val),
);
}).toList(),
onChanged: (val) {
debugPrint('selected option: $val');
},
)
],
),
),
);
}
}
导入“包装:颤振/材料.省道”;
void main()=>runApp(MyApp());
类MyApp扩展了无状态小部件{
@凌驾
小部件构建(构建上下文){
返回材料PP(
主页:MyHomeapp(),
);
}
}
类MyHomeapp扩展StatefulWidget{
@凌驾
状态createState(){
返回新的MyHomeappstate();
}
}
类MyHomeappstate扩展了状态{
字符串值=“”;
列表值=[];
@凌驾
void initState(){
super.initState();
设置状态(){
addAll(['one','two']);
value=values.elementAt(0);
});
}
小部件构建(构建上下文){
归还新脚手架(
appBar:新的appBar(
标题:新文本(“下拉演示”),
),
主体:新容器(
子:新列(
儿童:[
新下拉按钮(
提示:容器(
子项:文本(“选择选项”),
),
项:values.map((字符串val){
返回新的DropdownMenuItem(
值:val,
子项:文本(val),
);
}).toList(),
一旦更改:(val){
debugPrint('selected option:$val');
},
)
],
),
),
);
}
}
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: MyHomeapp(),
);
}
}
class MyHomeapp extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return new MyHomeappstate();
}
}
class MyHomeappstate extends State<MyHomeapp> {
String value = '';
List<String> values = [];
@override
void initState() {
super.initState();
setState(() {
values.addAll(['one', 'two']);
value = values.elementAt(0);
});
}
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text("drop down demo"),
),
body: new Container(
child: new Column(
children: <Widget>[
new DropdownButton(
hint: Container(
child: Text('Select option'),
),
items: values.map((String val) {
return new DropdownMenuItem(
value: val,
child: Text(val),
);
}).toList(),
onChanged: (val) {
debugPrint('selected option: $val');
},
)
],
),
),
);
}
}