Lazy dependency injection template

dependency_injector.dart

import 'package:dio/dio.dart';
import 'package:dio/src/dio.dart';
import 'package:my_test_app/config/application_config.dart';
import 'package:my_test_app/dependency_injection/dependency_injector_base.dart';
import 'package:my_test_app/features/login/login_bloc.dart';
import 'package:my_test_app/features/login/login_service.dart';
import 'package:my_test_app/features/splash/splash_bloc.dart';
import 'package:my_test_app/features/splash/splash_service.dart';

class DependencyInjector extends DependencyInjectorBase {
  final Dio _dio = Dio(
    BaseOptions(
      baseUrl: ApplicationConfig.BASE_URL,
    ),
  );

  SplashBloc _splashBloc;
  SplashService _splashService;
  LoginBloc _loginBloc;
  LoginService _loginService;

  @override
  Dio get dio => _dio;

  @override
  SplashBloc get splashBloc {
    _splashBloc = buildIfDisposed(_splashBloc, () => SplashBloc(splashService));
    return _splashBloc;
  }

  @override
  SplashService get splashService {
    _splashService = buildIfDisposed(_splashService, () => SplashService(dio));
    return _splashService;
  }

  @override
  LoginBloc get loginBloc =>
      buildIfDisposed(_loginBloc, () => LoginBloc(loginService));

  @override
  LoginService get loginService =>
      buildIfDisposed(_loginService, () => LoginService(dio));
}

dependency_injector_base.dart

import 'package:dio/dio.dart';
import 'package:my_test_app/common/disposable.dart';
import 'package:my_test_app/features/login/login_bloc.dart';
import 'package:my_test_app/features/login/login_service.dart';
import 'package:my_test_app/features/splash/splash_bloc.dart';
import 'package:my_test_app/features/splash/splash_service.dart';

abstract class DependencyInjectorBase {
  Dio get dio;
  SplashBloc get splashBloc;
  SplashService get splashService;
  LoginBloc get loginBloc;
  LoginService get loginService;

  Disposable buildIfDisposed(Disposable dependency,
      [Disposable Function() builder]) {
    if (dependency?.disposed ?? true) {
      return builder?.call();
    } else {
      return dependency;
    }
  }
}

dependency_provider.dart

import 'package:flutter/material.dart';
import 'package:my_test_app/dependency_injection/dependency_injector_base.dart';

class DependencyProvider extends InheritedWidget {
  final DependencyInjectorBase injector;

  DependencyProvider({Key key, this.injector, Widget child})
      : super(key: key, child: child);

  @override
  bool updateShouldNotify(InheritedWidget oldWidget) {
    return false;
  }

  static DependencyInjectorBase dependencyInjectorOf(BuildContext context) {
    return context
        .dependOnInheritedWidgetOfExactType<DependencyProvider>()
        ?.injector;
  }
}

disposable.dart

import 'package:flutter/foundation.dart';

abstract class Disposable {
  bool _disposed = false;
  bool get disposed => _disposed;

  @protected
  void disposeInstance();

  void dispose() {
    disposeInstance();
    _markDisposed();
  }

  void _markDisposed() {
    _disposed = true;
  }
}

mock_injector.dart

import 'package:my_test_app/dependency_injection/dependency_injector.dart';
import 'package:my_test_app/features/login/login_bloc.dart';
import 'package:my_test_app/features/login/mock_login_bloc.dart';

class MockInjector extends DependencyInjector {
  MockLoginBloc _mockLoginBloc;
  @override
  LoginBloc get loginBloc =>
      buildIfDisposed(_mockLoginBloc, () => MockLoginBloc(loginService));
}