Koin Components

Sometimes you can't declare only components via Koin. Dependening on your runtime technology, you might need to retrieve instances from Koin in a class that was not created with Koin (e.g. Flutter Widgets)

The KoinComponent interface

Tag your class with the KoinComponent interface to unlock Koin injection features:

inject() - lazy inject an instance
get() - retrieve an instance

We can inject the module above into class properties:

// Tag class with KoinComponent
class HelloApp extends KoinComponent{
  // lazy inject dependency
  Lazy<HelloServiceImpl> helloService;
  
  HelloApp() {
    helloService = inject<HelloServiceImpl>();
  }

  void sayHello() {
    helloService.value.sayHello();
  }
}

If the class already inherits another one you can use KoinComponentMixin instead of inheriting KoinComponent.

// Tag class with KoinComponentMixin
class HelloApp extends App with KoinComponentMixin { 
  // lazy inject dependency
  Lazy<HelloServiceImpl> helloService;

  HelloApp() {
    helloService = inject<HelloServiceImpl>();
  }

  void sayHello() {
    helloService.value.sayHello();
  }
}

And we just need to start Koin and run our class:

// a module with our declared Koin dependencies 
final helloModule = module()..single((s) => HelloServiceImpl());

void main() {

    // Start Koin
    startKoin((app){
      app.module(helloModule);
    });
    
    // Run our Koin component
    HelloApp().sayHello();
}

Bootstrapping

KoinComponent interface is also used to help you bootstrap an application from outside of Koin. Also, you can bring KoinComponent feature by extension functions directly on some target classes. The koin_flutter pachage use extensions to provide the Koin API for Flutter Widgets.

Bridge with Koin instance

The KoinComponent interface brings the following:

abstract class KoinComponent {

    /**
     * Get the associated Koin instance
     */
    Koin getKoin() => KoinContextHandler.get();
}

It opens the following possibilties:

You can then redefine then getKoin() function to redirect to a local custom Koin instance

The KoinComponent interface#

Bootstrapping#

Bridge with Koin instance#

The KoinComponent interface

Bootstrapping

Bridge with Koin instance