颤振:下拉按钮设置状态不起作用

Question

我有一个DropDownButton，它是从SQLite数据库中填充的，目前对我的应用程序来说还可以。但在选择一个条目后，DropDownButton并没有显示所选的条目，只是显示提示。为了检查我的条目，我尝试用选择的条目填充文本字段，但这也没有改变。这是我的DropDownButton代码：

List<DropdownMenuItem<String>> teamList;
DropdownMenuItem selectedTeam;
DropdownButton(
hint: Text("Choose"),
value: selectedTeam,
onChanged: (value) {
setState(() {
_teamController.text = value.name;
selectedTeam = value;
});
},
items: teamList,
),

实际上，我在initstate中用一个代码片段填充了我的teamList：

super.initState();
teamList = [];
db.getData().then((listMap) {
listMap.map((map) {
print(map.toString());
return getDropDownWidget(map);
}).forEach((dropDownMenuItem) {
teamList.add(dropDownMenuItem);
});
setState(() {});
});

和这个：

DropdownMenuItem<String> getDropDownWidget(Map<String, dynamic> map) {
return DropdownMenuItem<String>(
value: map['team'],
child: Text(map['team']),
);

}

在我的dbhelper文件中，我有这样的代码：

Future<List<Map<String, dynamic>>> getData() async {
var dbClient = await db;
return await dbClient.rawQuery('SELECT team FROM teamTable');

}

Answer 1

Hey Thomas看看这个例子：

import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: SampleApp(),
debugShowCheckedModeBanner: false,
);
}
}
class SampleApp extends StatefulWidget {
@override
_SampleAppState createState() => _SampleAppState();
}
class _SampleAppState extends State<SampleApp> {
List<String> teamList = ['Sample', 'Sample2', 'Sample3', 'Sample4'];
String selectedTeam;
TextEditingController _teamController = TextEditingController();
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Your heading'),
),
body: Container(
child: Column(
children: <Widget>[
TextFormField(
controller: _teamController,
),
new DropdownButton<String>(
items: teamList.map((String value) {
return new DropdownMenuItem<String>(
value: value,
child: new Text(value),
);
}).toList(),
value: selectedTeam,
hint: Text('Choose'),


onChanged: (value) {
setState(() {
_teamController.text = value;
selectedTeam = value;
print('This is the selected value: $selectedTeam');
});
},
),
],
)));
}
}

如果有效，请告诉我。