Flutter - DropdownButtonFormField value not updating - dart

Question

My Dropdown button value doesn't update until the AlertDialog box is closed and reopened.
I have the variable set at the top of my class
class _ItemListState extends State<ItemList> {
int _ratingController;
...
}
Within the class I have an AlertDialog that opens a form, within here I have the DropdownButtonFormField
AlertDialog(
content: Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
TextField(
controller: _eateryController,
autofocus: true,
decoration:
InputDecoration(labelText: 'Eatery', hintText: 'eg Pizza Hut'),
),
TextField(
controller: _supplierController,
decoration: InputDecoration(
labelText: 'Supplier', hintText: 'eg Deliveroo'),
),
TextField(
controller: _descriptionController,
decoration: InputDecoration(
labelText: 'Description', hintText: 'eg cheese pizza'),
),
DropdownButtonFormField<int>(
value: _ratingController,
items: [1, 2, 3, 4, 5]
.map((label) => DropdownMenuItem(
child: Text(label.toString()),
value: label,
))
.toList(),
hint: Text('Rating'),
onChanged: (value) {
setState(() {
_ratingController = value;
});
},
),
],
),
actions: <Widget>[
FlatButton(
onPressed: () {
_handleSubmit(_eateryController.text, _supplierController.text,
_descriptionController.text, _ratingController);
Navigator.pop(context);
},
child: Text('Save'),
),
FlatButton(
onPressed: () => Navigator.pop(context),
child: Text('Cancel'),
)
],
);
the setState doesn't seem to be dynamically updating the fields value. The updated value will only show once I close and re open the AlertDialog.
How can I get this to update instantly?
Thanks

Answer 1

You need to create a new StatefulWidget class that should return your AlertDialog
class MyDialog extends StatefulWidget {
#override
_MyDialogState createState() => _MyDialogState();
}
class _MyDialogState extends State<MyDialog> {
int _ratingController;
#override
Widget build(BuildContext context) {
return AlertDialog(
content: Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
TextField(
controller: _eateryController,
autofocus: true,
decoration:
InputDecoration(labelText: 'Eatery', hintText: 'eg Pizza Hut'),
),
TextField(
controller: _supplierController,
decoration: InputDecoration(
labelText: 'Supplier', hintText: 'eg Deliveroo'),
),
TextField(
controller: _descriptionController,
decoration: InputDecoration(
labelText: 'Description', hintText: 'eg cheese pizza'),
),
DropdownButtonFormField<int>(
value: _ratingController,
items: [1, 2, 3, 4, 5]
.map((label) => DropdownMenuItem(
child: Text(label.toString()),
value: label,
))
.toList(),
hint: Text('Rating'),
onChanged: (value) {
setState(() {
_ratingController = value;
});
},
),
],
),
actions: <Widget>[
FlatButton(
onPressed: () {
_handleSubmit(_eateryController.text, _supplierController.text,
_descriptionController.text, _ratingController);
Navigator.pop(context);
},
child: Text('Save'),
),
FlatButton(
onPressed: () => Navigator.pop(context),
child: Text('Cancel'),
)
],
);
}
}
Use it like this
showDialog(
context: context,
builder: (context) {
return MyDialog();
},
);

Answer 2

You can use statefulBuilder inside alert dialog.
return AlertDialog(
title: new Text('Table'),
content: StatefulBuilder(builder:
(BuildContext context,
StateSetter setState) {
return Container(
child: new SingleChildScrollView(
scrollDirection: Axis.vertical,
child: new Column(
children: <Widget>[
DropdownButtonFormField<String>(
value: dropdownValue,
style: TextStyle(
color: Colors.black87),
items: <String>[
'Lot 1',
'Lot 2',
'Lot 3',
'Lot 4',
].map<
DropdownMenuItem<
String>>(
(String value) {
return DropdownMenuItem<
String>(
value: value,
child: Text(value),
);
}).toList(),
onChanged: (String newValue) {
setState(() {
dropdownValue = newValue;
});
},
),
```

Answer 3

It looks like you're calling setState in a wrong widget. The AlertDialog doesn't belong to ItemList's tree because it's located inside another Route. So calling setState inside _ItemListState won't rebuild the AlertDialog.
Consider pulling out content of AlertDialog into a separate StatefulWidget and putting int _ratingController into it's state.