Dropdown Button wont change - flutter

Question

Hi i got stuck while write flutter code on dropdown button, where after user choosed from the list the hint wont changed to what the user choose. Can anyone help ?
So here is my code:
DropdownButton(items: [
DropdownMenuItem(value: "1", child: Text('+')),
DropdownMenuItem(value: "2", child: Text('-')),
DropdownMenuItem(value: "3", child: Text('X')),
DropdownMenuItem(value: "4", child: Text('/'))
].toList(), onChanged: (value){
setState(() {
_value = value;
});
},hint: Text('Operation'),)

Answer 1

I have just created an example below just check it and let me know if it works :
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
title: 'Flutter Demo',
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> {
String selectedOperator;
var listOfOperators = [
Operators(type: "+ Addition", value: 1),
Operators(type: "- Substraction", value: 2),
Operators(type: "* Multiplication", value: 3),
Operators(type: "/ Division", value: 4),
];
#override
void initState() {
super.initState();
print(listOfOperators.length);
}
#override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
home: Scaffold(
body: Center(
child: Container(
child: Padding(
padding: const EdgeInsets.all(30.0),
child: Container(
height: 50,
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(5.0),
border: Border.all(
color: Colors.red, style: BorderStyle.solid, width: 0.80),
),
child: DropdownButton(
value: selectedOperator,
isExpanded: true,
icon: Padding(
padding: const EdgeInsets.only(left: 15.0),
child: Icon(Icons.arrow_drop_down),
),
iconSize: 25,
underline: SizedBox(),
onChanged: (newValue) {
setState(() {
print(newValue);
selectedOperator = newValue;
});
print(selectedOperator);
},
hint: Padding(
padding: const EdgeInsets.all(8.0),
child: Text('Select'),
),
items: listOfOperators.map((data) {
return DropdownMenuItem(
value: data.value.toString(),
child: Padding(
padding: const EdgeInsets.only(left: 10.0),
child: Text(
data.type,
style: TextStyle(
fontSize: 18,
color: Colors.black,
),
),
),
);
}).toList()),
),
),
),
),
),
);
}
}
class Operators {
String type;
int value;
Operators({this.type, this.value});
}

Answer 2

Here you go with running example:
String dropdownValue = 'Lahore';
#override
Widget build(BuildContext context) {
return DropdownButton<String>(
value: dropdownValue,
icon: Icon(Icons.arrow_downward),
iconSize: 24,
elevation: 16,
style: TextStyle(
color: Colors.deepPurple
),
underline: Container(
height: 2,
color: Colors.deepPurpleAccent,
),
onChanged: (String newValue) {
setState(() {
dropdownValue = newValue;
});
},
items: <String>['Lahore', 'Islamabad', 'Faisalabad', 'Attabad']
.map<DropdownMenuItem<String>>((String value) {
return DropdownMenuItem<String>(
value: value,
child: Text(value),
);
})
.toList(),
);
}