Flutter Riverpod - Initialize with async values

Question

I'm trying to learn Riverpod and I have a ChangeNotifierProvider that has a few fields that need to be initialized with a value that is returned from an async operation. Is this possible, as I know I cant create the ChangeNotifierProvider asynchronously?

Example ChangeNotifierProvider

class SomeState extends ChangeNotifier {
  String email = '';

  // needs to be set to value returned from
  // shared preferences upon init
}

If not possible, is there another provider that could work better knowing I want to initialize its value to the returned value from async method?

Answer 1

Yes, it is possible as Abion47's comment. Let me show more details in the code below

class EmailNotifier extends ChangeNotifier {
  String email = '';

  void load() {
    functionReturnFuture.then(value) {
      setEmail(value);
    }
  }

  void setEmail(String value) {
    // email loaded but not changed, so no need to notify the listeners
    if(value == email) return;

    // email has loaded and change then we notify listeners
    email = value;
    notifyListeners();
  }
}


var emailNotifier = ChangeNotifierProvider<EmailNotifier>((ref) {
  var notifier = EmailNotifier();

  // load the email asynchronously, once it is loaded then the EmailNotifier will trigger the UI update with notifyListeners
  notifier.load();
  return notifier;
});

As we manage state independently from Flutter UI, there is nothing blocking you from running code to trigger a state change, for example in our case notifier.load().

After notifier.load() and email is set then the provider will trigger UI change using notifyListeners().

You can achieve a similar result using FutureProvider.