dependon 0.0.4

Simple and light-weight package for dependency injection management.

Simple and light-weight package for dependency injection management.

Features

• Create modules to organize your application's dependencies
• Easy to learn
• Supports Inversion of Control
• Lazy initialization by default

Getting started

1. Add the dependency to your pubspec.yaml.
2. Create your first module

import 'package:dependon/dependon.dart';

class RepositoryModule extends Module {
  @override
  void dependencies() {
    singleton<UserRepository>(() => UserRepositoryImpl(get()));
  }
}

3. Load your module

import 'package:dependon/dependon.dart';

void main() {
  final di = DependencyInjection.instance;
  di.loadModule(RepositoryModule());
  // ...
  runApp(myApp);
}

4. Retrieve your classes

import 'package:dependon/dependon.dart';

final UserRepository userRepository = get();

Module

A Module is a logical component that organizes and split your concepts behind your application. In a complex architecture you probabily will need to deal with lots of repositories, use cases, abstractions, concrete implementations and other lots of challanges. For a better organization, you can split all those things into Modules.

Let's take a look at this sample:

import 'package:dependon/dependon.dart';

class RepositoryModule extends Module {
	@override
	void dependencies() {
		singleton<CounterRepository>(() => CounterRepositoryImpl(get()));
	}
}

class UseCaseModule extends Module {
	@override
	void dependencies() {
		factori<IncrementCounterUseCase>(() => IncrementCounterUseCase(get()));
	}
}

void main() {
	DependencyInjection.instance.loadModules([
		RepositoryModule(),
		UseCaseModule(),
	]);
}

Property

A property is an object that holds an instance of another object. Note that an object is not lazy initialized, because will pass the instance of the object in the declaration's moment.

import 'package:dependon/dependon.dart';

class SettingsModule extends Module {
	@override
	void dependencies() {
		if (isDebug()) {
			property<WebServiceConfig>(MockWebServiceConfig());
		} else {
			property<WebServiceConfig>(WebServiceConfigImpl());
		}
	}
}

Singleton

In software engineering, the singleton pattern is a software design pattern that restricts the instantiation of a class to one "single" instance. This is useful when exactly one object is needed to coordinate actions across the system. (https://en.wikipedia.org/wiki/Singleton_pattern)

import 'package:dependon/dependon.dart';

class RepositoryModule extends Module {
	@override
	void dependencies() {
		singleton<CounterRepository>(() => CounterRepositoryImpl(get()));
		singleton<UserRepository>(() => UserRepositoryImpl());
	}
}

Factory

In this case, the Factory object holds the instruction of initialization of an object, and each time get() is called a new instance of that object will be created. In our package the initilization of a factory is using the keyword factori and this is because the name factory is already in use by Flutter's core.

import 'package:dependon/dependon.dart';

class BlocModule extends Module {
	@override
	void dependencies() {
		factori<HomeBloc>(() => HomeBloc(get(), get(), get()));
	}
}

Best pratices

1. Avoid using get() everywhere in you application.

Instead of using get() everytime you need an instance of a class, prefer passing your needs by constructor. That will help you a lot when you need to write a test.

Bad:

import 'package:dependon/dependon.dart';

class MyUseCase {
	final MyRepository _myRepository = get();
	// ...
}

Good:

import 'package:dependon/dependon.dart';

class MyUseCase {
	final MyRepository _myRepository;

	MyUseCase(this._myRepository);
}

2. Respect the conceptual ordering

Almost everything in DependOn is lazy initialized which means that the risk of having an unneccessary initialization of some object is minimal. But in some cases we need to pass our properties accross the application, and those properties are not lazy initialized. That means we must always declare our properties before our factories and singletons.

Bad:

import 'package:dependon/dependon.dart';

class AppModule extends Module {
	@override
	void dependencies() {
		singleton<UserRepository>(() => UserRepositoryImpl(get()));
		property<WebServiceConfig>(WebServiceConfigImpl());
	}
}

Good:

import 'package:dependon/dependon.dart';

class AppModule extends Module {
	@override
	void dependencies() {
		property<WebServiceConfig>(WebServiceConfigImpl());
		singleton<UserRepository>(() => UserRepositoryImpl(get()));
	}
}

Additional information

This is an alpha release and this package is still in development. Not recommended for production.