[英]There should be exactly one item with [DropdownButton]'s value:
String selectedItem = 'Instalação Fibra';
DropdownButton<String>(
value: selectedItem,
onChanged: (value) {
setState(() {
selectedItem = value;
});
},
items: <String>['Instalação de TV', 'Instalação Rádio']
.map<DropdownMenuItem<String>>((String e) {
return DropdownMenuItem<String>(
value: e,
child: Text(e),
);
}).toList(),
)
這怎么會是錯的? 這不是編譯。 我嘗試了幾種方法,但都出現了同樣的錯誤。
您可以在下面復制粘貼運行完整代碼
<String>['Instalação de TV', 'Instalação Rádio']
中不存在selectedItem
'Instalação Fibra'
您可以使用List<String> items
並設置selectedItem = items[0]
代碼片段
List<String> items = ['Instalação Fibra','Instalação de TV', 'Instalação Rádio'];
String selectedItem;
@override
void initState() {
selectedItem = items[0];
super.initState();
}
工作演示
完整代碼
import 'package:flutter/material.dart';
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> {
List<String> items = ['Instalação Fibra','Instalação de TV', 'Instalação Rádio'];
String selectedItem;
@override
void initState() {
selectedItem = items[0];
super.initState();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: DropdownButton<String>(
value: selectedItem,
onChanged: (value) {
setState(() {
selectedItem = value;
});
},
items: items.map<DropdownMenuItem<String>>((String e) {
return DropdownMenuItem<String>(
value: e,
child: Text(e),
);
}).toList(),
),
);
}
}
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.