如何修复：必须初始化不可为 null 的实例字段“userFuture”？

Question

This is my code for main.dart:

 class HomePage extends StatefulWidget {
  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
Future userFuture; //error is here

  Future<List<String>> getData() async {
    var databaseRef2 = FirebaseDatabase.instance.reference();
    databaseRef2 = FirebaseDatabase.instance.reference().child("Sliders");
    DatabaseEvent event = await databaseRef2.once();
    Map<dynamic, dynamic> values =
        event.snapshot.value as Map<dynamic, dynamic>;
    values.forEach((key, values) {
      imgList.add(values["img"]);
    });
    return imgList;
  }

  }
}

If I declare Future as:

Future userFuture;

I get this error:

Non-nullable instance field 'userFuture' must be initialized.
Try adding an initializer expression, or a generative constructor that initializes it

Please tell me how to fix it? Thanks in advance

Answer 1

As per flutter null-safety try to add?

 Future? userFuture;

Or

late Future  userFuture;

Answer 2

Well from sdk 2.12 onwards, dart supports null-safety
there are two ways to fix this error, since you haven't mentioned the use of userFuture.

1. add late keyboard before the initialisation late Future userFuture
2. add null safety operator Future? userFuture Future? userFuture