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How to have async calls at the creation of an ChangeNotifier in Dart / Flutter?

class FoldersProvider extends ChangeNotifier {
  final _folders = <Directory>[];

  FoldersProvider() {
    _addDefaultFoldersIfAccessible();
  }
// more code
}

_addDefaultFoldersIfAccessible is an async function.

I normally should await the Future<void> result

but I can’t make the constructor async and I should still be able to instantiate it like a regular ChangeNotifier so it can still work as intended in my Flutter App.

Do you have any solution?

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2

Answers


  1. 0

    You can initialize the result value of _addDefaultFoldersIfAccessible as a "warm-up data" before running your app. To allow smooth transition, you can use runApp twice in your main function so that you can show a widget (perhaps a loading screen) before your main app is running.

    // main.dart
Future<void> main() async {
  runApp(const LoadingScreen());  
  await yourInitializingFunction();
  runApp(const MyApp());
}

    Ideally, yourInitializingFunction should handle all the necessary async tasks that are required by the ChangeNotifier so that you don’t need to make _addDefaultFoldersIfAccessible async anymore.

    See also:

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  2. 0

    Since you can’t apply async to the body of a constructor you could try the following:

    FoldersProvider() {
_addDefaultFoldersIfAccessible().then((value) => someAction);
}

    If you replace someAction with what you want to do when _addDefaultFoldersIfAccessible is complete. This value can be null.

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