flutter - 如何在上下文中结合 Flutter 中的 DropdownMenu 和 AppLocalization?
问题描述
我在与 AppLocalization 一起使用下拉菜单时遇到问题。我已经根据用户在电话设置中选择的语言实现了自动本地化。在我想用本地化值实现下拉菜单之前,它工作得很好。当我渲染下拉菜单时,它可以工作,但是在我选择值后,会出现类似Flutter 的错误:应该只有一个项目具有 [DropdownButton] 的值,请注意我需要在 KeyValueRecords 列表中使用 appLocalization,
import 'package:MyHorse.sk/app_localizations.dart';
class AddNewTrainingFormState extends State<AddNewTrainingForm> {
KeyValueRecordType recordType;
@override
Widget build(BuildContext context) {
List<KeyValueRecordType> recordTypes = <KeyValueRecordType>[
KeyValueRecordType(
key: "dressage",
value: AppLocalizations.of(context).translate('dressage')),
KeyValueRecordType(
key: "cavaletti",
value: AppLocalizations.of(context).translate('cavaletti')),
KeyValueRecordType(
key: "jumping",
value: AppLocalizations.of(context).translate('jumping')),
KeyValueRecordType(
key: "hacking",
value: AppLocalizations.of(context).translate('hacking')),
KeyValueRecordType(
key: "groundwork",
value: AppLocalizations.of(context).translate('groundwork')),
KeyValueRecordType(
key: "competition",
value: AppLocalizations.of(context).translate('competition')),
KeyValueRecordType(
key: "other", value: AppLocalizations.of(context).translate('other')),
];
return Scaffold(
body: Container(
child: Theme(
data: Theme.of(context).copyWith(
canvasColor: Colors.black,
),
child: DropdownButton<KeyValueRecordType>(
value: recordType,
onChanged: (KeyValueRecordType value) {
setState(() {
recordType = value; //show selected value
});
},
items: recordTypes
.map<DropdownMenuItem<KeyValueRecordType>>(
(recordType) =>
new DropdownMenuItem<KeyValueRecordType>(
child: Text(recordType.value),
value: recordType,
))
.toList(),
),
),
class KeyValueRecordType {
String key;
String value;
KeyValueRecordType({this.key, this.value});
}
所以错误是:
There should be exactly one item with [DropdownButton]'s value: Instance of 'KeyValueRecordType'.
I/flutter ( 9900): Either zero or 2 or more [DropdownMenuItem]s were detected with the same value
I/flutter ( 9900): 'package:flutter/src/material/dropdown.dart':
I/flutter ( 9900): Failed assertion: line 834 pos 15: 'items == null || items.isEmpty || value == null ||
I/flutter ( 9900): items.where((DropdownMenuItem<T> item) {
I/flutter ( 9900): return item.value == value;
I/flutter ( 9900): }).length == 1'
我尝试了不同的方法,当我在 onchanged 中指定 recordType.key 时,我收到此键不存在的错误。我也尝试将 List 放在 FutureBuilder 和单独的函数中,但都不起作用。由于我需要 Context 我不能把它放在构建方法之外。
解决方案
您可以在下面复制粘贴运行完整代码
您可以使用包https://pub.dev/packages/equatable并扩展Equatable
代码片段
import 'package:equatable/equatable.dart';
...
class KeyValueRecordType extends Equatable {
String key;
String value;
KeyValueRecordType({this.key, this.value});
@override
List<Object> get props => [key, value];
}
工作演示
完整代码
import 'package:equatable/equatable.dart';
import 'package:flutter/material.dart';
class KeyValueRecordType extends Equatable {
String key;
String value;
KeyValueRecordType({this.key, this.value});
@override
List<Object> get props => [key, value];
}
class AddNewTrainingForm extends StatefulWidget {
@override
AddNewTrainingFormState createState() => AddNewTrainingFormState();
}
class AddNewTrainingFormState extends State<AddNewTrainingForm> {
KeyValueRecordType recordType;
@override
Widget build(BuildContext context) {
List<KeyValueRecordType> recordTypes = <KeyValueRecordType>[
KeyValueRecordType(key: "dressage", value: 'dressage'),
KeyValueRecordType(key: "cavaletti", value: 'cavaletti'),
KeyValueRecordType(key: "jumping", value: 'jumping'),
KeyValueRecordType(key: "hacking", value: 'hacking'),
KeyValueRecordType(key: "groundwork", value: 'groundwork'),
KeyValueRecordType(key: "competition", value: 'competition'),
KeyValueRecordType(key: "other", value: 'other'),
];
return SafeArea(
child: Scaffold(
body: Container(
child: Theme(
data: Theme.of(context).copyWith(
canvasColor: Colors.white,
),
child: DropdownButton<KeyValueRecordType>(
value: recordType,
onChanged: (KeyValueRecordType value) {
setState(() {
recordType = value; //show selected value
});
},
items: recordTypes
.map<DropdownMenuItem<KeyValueRecordType>>(
(recordType) => new DropdownMenuItem<KeyValueRecordType>(
child: Text(recordType.value),
value: recordType,
))
.toList(),
),
),
)),
);
}
}
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: AddNewTrainingForm(),
);
}
}
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