how to solve dynamic list type casting error in Hive?

Question

sorry I am new in using Flutter and using Hive local storage.

I am using

  hive: ^2.0.4
  hive_flutter: ^1.0.0

I open the box in main function like this

Future<void> main() async {

  await Hive.initFlutter();
  await Hive.openBox<List<Event>>("events");

}

after getting the data from the server, I save all the events to hive by using code like this

final eventsBox = Hive.box<List<Event>>("events");
final List<Event> eventsFromServer = await getEventsFromServer();
eventsBox.put("recommended_events", eventsFromServer);

but I have error when trying to read the data from the box, I read it like this

final eventsBox = Hive.box<List<Event>>("events");

// error in this one line below
final eventsFromHive = eventsBox.get("recommended_events", defaultValue: []) ?? []; 

type 'List < dynamic > ' is not a subtype of type 'List< Event >?' in type cast

how to solve this type casting error?

from the documentation in here it is said

Lists returned by get() are always of type List (Maps of type Map<dynamic, dynamic>). Use list.cast() to cast them to a specific type.

I don't know if it is the solution of my problem or not, but I don't know how to implement that in my code.

I tried it like this, but I still have the same error

final eventsFromHive = eventsBox.get("recommended_events")!.cast<Event>();

or maybe the way I write the syntax to save and read the list are totally wrong? please help :)

Solution 1

Is not necessary to open your box as a List, because it is a box and can store many objects of the type that you declare, for example:

await Hive.openBox<MyModel>(boxName);

To get all the objects or data stored in that box, you can query like this:

final box = Hive.box<CompanyModel>(boxName);
List<CompanyModel> interviews = box.values.toList();

In addition, you have to create an Adapter Model if you want to store your own Model with Hive.

There is two dev dependencies to auto generate the Model:

dev_dependencies: 
  hive_generator: 
  build_runner: 

Importing that dependencies and running this command flutter packages pub run build_runner build will generate the Model, but also you have to create your Model as the documentation indicates.

I suggest you to check out the documentation.

Hive - Generate Adapter

Solution 2

I can finally solve it by using it like this. in main function

Future<void> main() async {

  await Hive.initFlutter();
  await Hive.openBox("events");

}

when saving data list

final eventsBox = Hive.box("events");
eventsBox.put("recommended_events", eventsFromServer);

and read it like this

final eventsBox = Hive.box("events");
final eventsFromHive = eventsBox.get("recommended_events")?.cast<Event>() ?? [];

Comments

[Lakmal Fernando]

final eventsFromHive = eventsBox.get("recommended_events", defaultValue: <Event>[]) ?? [];

[Alexa289]

@sajithlakmal unfortunately it doesn't work :(

[Lakmal Fernando]

What is you Event object

[sungkd123]

Can you please post your events model class definition