Flutter DropdownButtonFormField not updating variable - flutter

Question

So I am struggling with the DropdownButtonFormField where when you change the value it runs the onChange function with the updated value. However, once the onChange finishes the value variable seems to reset itself meaning it never changes.
This is a cut-down version of the full form:
final _formKey = GlobalKey<FormState>();
TextEditingController assetGroupNameController = new TextEditingController();
TextEditingController assetGroupDescriptionController = new TextEditingController();
String assetGroupTypeController;
Widget build(BuildContext context) {
ProgressDialog pr;
assetGroupNameController.text = widget.assetGroup.name;
assetGroupDescriptionController.text = widget.assetGroup.description;
assetGroupTypeController = widget.assetGroup.type;
return ListView(
children: <Widget>[
Card(
elevation: 13.0,
child: Form(
key: _formKey,
child: DropdownButtonFormField(
value: assetGroupTypeController,
items: assetGroupTypes.map((f) {
return new DropdownMenuItem<String>(
value: f['key'],
child: new Text(f['text']),
);
}).toList(),
onChanged: (value) {
typeDropdownChange(value);
})
)
)
);
}
void typeDropdownChange(value) {
setState(() {
assetGroupTypeController = value;
});
}

Answer 1

You assigned the controller directly to value parameter of DropdownButtonFormField and you have string value for DropdownMenuItem. You should be storing the same data type value. Check below example and modify your code accordingly
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Material(
child: Center(
child: new MyDropDown(),
),
),
);
}
}
class MyDropDown extends StatefulWidget {
const MyDropDown({
Key key,
}) : super(key: key);
#override
_MyDropDownState createState() => _MyDropDownState();
}
class _MyDropDownState extends State<MyDropDown> {
String selected;
#override
Widget build(BuildContext context) {
return DropdownButtonFormField<String>(
value: selected,
items: ["Item 1", "Item 2", "Item 3"]
.map((label) => DropdownMenuItem<String>(
child: Text(label),
value: label,
))
.toList(),
onChanged: (value) {
setState(() => selected = value);
},
);
}
}