I have created two DropdownButtons in the appBar and in the Body of a Scaffold.The Top DropdownButton changes the language whenever it is selected.After I selected One Conversion rate from the second Dropdown Button and Change the Language, the code crushes.Here is the Code..
import 'package:flutter/material.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
primarySwatch: Colors.blue),
home: new MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => new _MyHomePageState();
}
class User {
User(this.name);
final String name;
}
class CurrencyClass {
final String currencyType;
CurrencyClass(this.currencyType);
}
class _MyHomePageState extends State<MyHomePage> {
User selectedUser;
CurrencyClass selectedCurrency;
List<User> users = <User>
[User('English'),User('Amharic'),User('Oromigna'),
User('Tigrigna'),User('Somali')];
List<CurrencyClass> currency = <CurrencyClass>[
CurrencyClass('USD'),
CurrencyClass('GBP'),
CurrencyClass('CAD'),
CurrencyClass('AUD'),
CurrencyClass('EURO'),CurrencyClass('SAR'),];
@override
void initState() {
super.initState();
selectedUser = users[0];
}
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
actions: <Widget>[
DropdownButton<User>(
value: selectedUser,
onChanged:(User newValue){
setState(() {
selectedUser = newValue;
if(newValue == users[0]){
currency = <CurrencyClass>[CurrencyClass('English'),CurrencyClass('CAD'),CurrencyClass('AUD'),CurrencyClass('EURO'),CurrencyClass('SAR')];
}
else if(newValue == users[1]){
currency = <CurrencyClass>[CurrencyClass('Amharic'),CurrencyClass('CAD'),CurrencyClass('AUD'),CurrencyClass('EURO'),CurrencyClass('SAR')];
}
else if(newValue == users[2]){
currency = <CurrencyClass>[CurrencyClass('Oromigna'),CurrencyClass('CAD'),CurrencyClass('AUD'),CurrencyClass('EURO'),CurrencyClass('SAR')];
} else if(newValue == users[3]){
currency = <CurrencyClass>[CurrencyClass('Tigringa'),CurrencyClass('CAD'),CurrencyClass('AUD'),CurrencyClass('EURO'),CurrencyClass('SAR')];
} else {
currency = <CurrencyClass>[CurrencyClass('Somaligna'),CurrencyClass('CAD'),CurrencyClass('AUD'),CurrencyClass('EURO'),CurrencyClass('SAR')];
}
});
},
items: users.map((User user){
return new DropdownMenuItem<User>(
value: user,
child:Text(
user.name,
style: TextStyle(color: Colors.black),
),
);
}).toList(),
)
],
),
body: new Center(
child: new Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
new Padding(padding: EdgeInsets.symmetric(vertical: 50.0),),
new Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text('Amount',style: TextStyle(fontSize: 20.0),),
Padding(padding: EdgeInsets.symmetric(horizontal: 15.0)),
Text('Birr',style: TextStyle(fontSize: 24.0),),
Padding(padding: EdgeInsets.symmetric(horizontal: 15.0)),
DropdownButton<CurrencyClass>(
value: selectedCurrency,
onChanged: (CurrencyClass newExchange){
setState(() {
selectedCurrency = newExchange;
});
},
items: currency.map((CurrencyClass user2){
return DropdownMenuItem<CurrencyClass>(
value: user2,
child: Text(
user2.currencyType,
style: TextStyle(color: Colors.red),
),
);
}).toList(),
),
],
),
],
),
),
);
}
}
Here is the Error when I select the top DropdownButton after selecting some value in the bottom dropdownButton
Launching lib/main.dart on XT1068 in debug mode...
Built build/app/outputs/apk/debug/app-debug.apk.
I/FlutterActivityDelegate(11200): onResume setting current activity to
this
I/flutter (11200): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY
╞═══════════════════════════════════════════════════════════
I/flutter (11200): The following assertion was thrown building
MyHomePage(dirty, state: _MyHomePageState#3ce11):
I/flutter (11200): 'package:flutter/src/material/dropdown.dart': F
Failed assertion: line 481 pos 15: 'value == null ||
I/flutter (11200): items.where((DropdownMenuItem<T> item) =>
item.value == value).length == 1': is not true.
I/flutter (11200): Either the assertion indicates an error in the
framework itself, or we should provide substantially
I/flutter (11200): more information in this error message to help you
determine and fix the underlying cause.
The problem in the original post is when setting the currency values on selecting the bar dropdown. You need to also set the selectedCurrency.
selectedCurrency = currency[0];
Or do what Gunter did in the edit. Just do not change the currency dropdown so there is no problem at all.
onChanged:(User newValue){
setState(() {
selectedUser = newValue;
if(newValue == users[0]){
currency = <CurrencyClass>[CurrencyClass('English'),CurrencyClass('CAD'),CurrencyClass('AUD'),CurrencyClass('EURO'),CurrencyClass('SAR')];
}
else if(newValue == users[1]){
currency = <CurrencyClass>[CurrencyClass('Amharic'),CurrencyClass('CAD'),CurrencyClass('AUD'),CurrencyClass('EURO'),CurrencyClass('SAR')];
}
else if(newValue == users[2]){
currency = <CurrencyClass>[CurrencyClass('Oromigna'),CurrencyClass('CAD'),CurrencyClass('AUD'),CurrencyClass('EURO'),CurrencyClass('SAR')];
}
else if(newValue == users[3]){
currency = <CurrencyClass>[CurrencyClass('Tigringa'),CurrencyClass('CAD'),CurrencyClass('AUD'),CurrencyClass('EURO'),CurrencyClass('SAR')];
}
else {
currency = <CurrencyClass>[CurrencyClass('Somaligna'),CurrencyClass('CAD'),CurrencyClass('AUD'),CurrencyClass('EURO'),CurrencyClass('SAR')];
}
selectedCurrency = currency[0];
});
},