How do I define a TypeAdapter?

Question

I am currently using the Hive database to store data. I run the below code:

main() async {
  runApp(MyApp());
  await Hive.initFlutter();
  Hive.registerAdapter(exerciseAdapter());
  await Hive.openBox('exerciseBox');
  SystemChrome.setPreferredOrientations([
    DeviceOrientation.portraitUp,
  ]);
} 

But it says exerciseAdapter() is not defined. How do I register this type adapter?

Answer 1

I cannot see your imports, but it seems you haven't defined the exerciseAdapter() method or imported it from another file. To register a type adapter in Hive, you need to create a custom adapter for your class (e.g., Exercise) and then register it using Hive.registerAdapter().

First, you need to create the custom adapter for your Exercise class. Assuming you have a class called Exercise, follow these steps:

Add hive_generator and build_runner dependencies to your pubspec.yaml file:

dependencies:
  hive: ^2.2.3
  ...

dev_dependencies:
  hive_generator: ^2.0.0
  build_runner: ^2.3.3
  ...

Create a file for your Exercise class (e.g., exercise.dart) and import the required packages:

import 'package:hive/hive.dart';

part 'exercise.g.dart';

Define your Exercise class and annotate it with @HiveType:

@HiveType(typeId: 0)
class Exercise extends HiveObject {
  @HiveField(0)
  String name;

  @HiveField(1)
  int duration;

  Exercise({required this.name, required this.duration});
}

Run the build command to generate the adapter file exercise.g.dart:

flutter pub run build_runner build

Finally, import the generated adapter file and register it in your main() function:

import 'package:hive/hive.dart';
import 'package:hive_flutter/hive_flutter.dart';
import 'package:flutter/services.dart';
import 'exercise.dart';

void main() async {
  await Hive.initFlutter();
  Hive.registerAdapter(ExerciseAdapter());
  await Hive.openBox<Exercise>('exerciseBox');

  SystemChrome.setPreferredOrientations([
    DeviceOrientation.portraitUp,
  ]);

  runApp(MyApp());
}