Flutter : using changeNotifier and provider when the context is not available - flutter

Question

I'm trying to use the simple state management described in the Flutter docs, using a ChangeNotifier, a Consumer, and a ChangeNotifierProvider.
My problem is that I can't get a hold a on valid context to update my model (details below...). I get an error:
Error: Error: Could not find the correct Provider above this CreateOrganizationDialog Widget
This likely happens because you used a BuildContext that does not include the provider of your choice. There are a few common scenarios:
The provider you are trying to read is in a different route.
Providers are "scoped". So if you insert of provider inside a route, then other routes will not be able to access that provider.
You used a BuildContext that is an ancestor of the provider you are trying to read.
Make sure that CreateOrganizationDialog is under your MultiProvider/Provider.
This usually happen when you are creating a provider and trying to read it immediately.
Here are extracts of my code:
class OrganizationModel extends ChangeNotifier {
final List<Organization> _items = [];
/// An unmodifiable view of the items in the cart.
UnmodifiableListView<Organization> get items => UnmodifiableListView(_items);
void addList(List<Organization> items) {
_items.addAll(items);
notifyListeners();
}
}
This is my model.
class OrganizationBodyLayout extends StatelessWidget {
Future<void> _showCreateOrganizationDialog() async {
return showDialog<void>(
context: navigatorKey.currentState.overlay.context,
barrierDismissible: false,
child: CreateOrganizationDialog());
}
_onCreateOrganizationPressed() {
_showCreateOrganizationDialog();
}
_onDeleteOrganizationPressed() {
//TODO something
}
_onEditOrganizationPressed() {
//TODO something
}
#override
Widget build(BuildContext context) {
return Container(
child: Column(mainAxisSize: MainAxisSize.max, children: [
ButtonBar(
alignment: MainAxisAlignment.start,
mainAxisSize: MainAxisSize.max,
children: <Widget>[
RaisedButton(
onPressed: _onCreateOrganizationPressed,
child: Text("New Organization"),
),
],
),
Expanded(
child: Container(
color: Colors.pink,
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
Expanded(
child: ChangeNotifierProvider(
create: (context) => OrganizationModel(),
child: OrganizationListView(),
)),
Expanded(child: Container(color: Colors.brown))
]))),
]));
}
}
A stateless widget that contains a ChangeNotifierProvider just on top of the list widget using the model.
On a button click, a modal dialog is shown, then data is fetched from the network. I should then update my model calling the addList operation.
Below is the code for the stateful dialog box.
class CreateOrganizationDialog extends StatefulWidget {
#override
_CreateOrganizationDialogState createState() =>
_CreateOrganizationDialogState();
}
class _CreateOrganizationDialogState extends State<CreateOrganizationDialog> {
TextEditingController _nametextController;
TextEditingController _descriptionTextController;
#override
initState() {
_nametextController = new TextEditingController();
_descriptionTextController = new TextEditingController();
super.initState();
}
#override
Widget build(BuildContext context) {
return Dialog(
child: Container(
width: 200,
height: 220,
child: Column(
children: [
Text('New organization',
style: Theme.of(context).textTheme.headline6),
Padding(
padding: EdgeInsets.all(8.0),
child: TextFormField(
decoration: new InputDecoration(hintText: "Organization name"),
controller: _nametextController,
),
),
Padding(
padding: EdgeInsets.all(8.0),
child: TextFormField(
decoration:
new InputDecoration(hintText: "Organization description"),
controller: _descriptionTextController,
),
),
ButtonBar(
children: [
FlatButton(
child: new Text("Cancel"),
onPressed: () {
Navigator.of(context).pop();
},
),
FlatButton(
child: new Text("Create"),
onPressed: () {
setState(() {
Future<Organization> organization =
backendCreateOrganization(_nametextController.text,
_descriptionTextController.text);
organization.then((value) {
Future<List<Organization>> organizations =
backendReloadOrganizations();
organizations.then((value) {
var model = context.read<OrganizationModel>();
// var model = navigatorKey.currentState.overlay.context.read<OrganizationModel>();
//model.addList(value);
});
});
});
Navigator.of(context).pop();
//context is the one for the create dialog here
},
)
],
)
],
),
));
}
}
My problem happens at the line
var model = context.read<OrganizationModel>();
Thinking of it, the context available here is the modal dialog box context - so it's kind of logical that the Provider is not found in the widget tree.
However, I can't see how to retrieve the proper context (which would be the one for the result list view, where the Provider is located) in order to get the model and then update it.
Any idea is welcome :-)

Answer 1

Solved (kind of).
The only way I've found to solve this is by making my model a global variable:
var globalModel = OrganizationModel();
And referencing this global model in all widgets that consume it. I can't find a way to find the context of a stateless widget from within a callback in another stateful widget.
It works, but it's ugly. Still open to elegant solutions here :-)

Answer 2

Get_it seems to be elegant way of sharing models across the application. Please check the documentation for the different use cases they provide.
You could do something like the following
GetIt getIt = GetIt.instance;
getIt.registerSingleton<AppModel>(AppModelImplementation());
getIt.registerLazySingleton<RESTAPI>(() =>RestAPIImplementation());
And in other parts of your code, you could do something like
var myAppModel = getIt.get<AppModel>();