Dart

Getting Started with Dart

This tutorial lets you write a Dart application and use Koin inject and retrieve your components.

Setup

First, check that the koin package dependency is added like below:

Package	Pub
koin

dependencies:

koin: ^[laste_version]

The application

In our small app we need to have 2 components:

• HelloMessageData - hold data
• HelloService - use and display data from HelloMessageData
• HelloApplication - retrieve and use HelloService

Data holder

Let's create a HelloMessageData data class to hold our data:

//

// A class to hold our message data

//

class HelloMessageData {

final message = "Hello Koin!";

}

Service

Let's create a service to display our data from HelloMessageData. Let's write HelloServiceImpl class and its interface HelloService:

//

// Hello Service - interface

//

abstract class HelloService {

String hello();

}

// Hello Service Impl

// Will use HelloMessageData data

class HelloServiceImpl implements HelloService {

final HelloMessageData helloMessageData;

HelloServiceImpl(this.helloMessageData)

@override

String hello(){

return "Hey, ${helloMessageData.message}";

}

}

The application class

To run our HelloService component, we need to create a runtime component. Let's write a HelloApplication class and tag it with KoinComponent interface. This will later allows us to use the get() functions to retrieve our component:

// HelloApplication - Application Class

// use HelloService

class HelloApplication extends KoinComponent {

// Inject HelloService

final helloService = get<HelloService>();

// display our data

static sayHello(){

print(helloService.hello());

}

}

Declaring dependencies

Now, let's assemble HelloMessageData with HelloService, with a Koin module:

final helloModule = Module()

..single((s) => HelloMessageData())

..single<HelloService>((s) => HelloServiceImpl(s.get()))

We declare each component as single, as singleton instances.

• single((s) => HelloMessageData()) : declare a singleton of HelloMessageData instance
• single<HelloService>((s) => HelloServiceImpl(s.get())) : Build HelloServiceImpl with injected instance of HelloMessageData, declared as singleton of HelloService.

That's it!

Just start our app from a main function:

void main() {

startKoin((app) {

app.printLogger(level: Level.debug);

app.module(helloModule);

});

HelloApplication().sayHello();

}