Hello Im working on flutter app using changenotifier for state managment In fact Im trying to intialize a list with async function result but I get this error: Uncaught Error: TypeError: Instance of '_Future<dynamic>': type '_Future<dynamic>' is not a subtype of type 'List<Location>'

class MapMarker extends ChangeNotifier{

   List<Location> locationsList = [];
   MapMarker(){
     LocationsDatabase.instance.getAllLocations().then((value) => locationsList=value);
   }



   static getAllLocations()  {
    List<Location> a = await LocationsDatabase.instance.getAllLocations();
    return  a
  }



}

any ideas how to do that ?

CodePudding user response：

I would consider reworking the class so that the static method creates an instance of Example, rather than the constructor calling the static method.

class Example {
  List<int> abc;
  Example(this.abc);

  static Future<Example> fill() async {
    return Example(await Future.delayed(const Duration(seconds: 2), () {
      return [1, 2, 3];
    }));
  }
}

void main() async {
  print((await Example.fill()).abc);
}

The MapMarker example can be updated in the same way.

class MapMarker extends ChangeNotifier {
  List<Location> locationsList;
  MapMarker(this.locationsList);

  static Future<MapMarker> getMapMarkerWithLocations() async {
    return MapMarker(await LocationsDatabase.instance.getAllLocations());
  }
}

But since you are using a ChangeNotifier why not simply add a call to notifyListeners()?

class MapMarker extends ChangeNotifier {
  List<Location> locationsList = [];
  MapMarker() {
    LocationsDatabase.instance.getAllLocations().then((value) {
      locationsList = value;
      notifyListeners();
    });
  }
}

CodePudding user response：

Small change on you code

class Example {
  Future<List<int>>? abc = null;

  Example() {
    initial();
  }

  initial() async {
    abc = fill();
  }

  static Future<List<int>> fill() async {
    return await Future.delayed(const Duration(seconds: 2), () {
      return [1, 2, 3];
    });
    // return [];
  }
}

main() async {
  print((await Example().abc));
}

output:

[1, 2, 3]

Maper

class MapMarker extends ChangeNotifier{

  Future<List<Location>>? locationsList = null;
  MapMarker(){
   initial();
  }
  initial() async {
    locationsList = fill();
  }


  static Future< List<Location>> getAllLocations() async  {
    List<Location> a = await LocationsDatabase.instance.getAllLocations();
    return  a;
  }



}