Definitions with Annotations

Koin Annotations allow to declare the same kind of definitions as the regular Koin DSL, but with annotations. Just tag your class with the needed annotation, and it will generate everything for you!

For example the equivalent to single { MyComponent(get()) } DSL declaration, is just done by tagging with @Single like this:

@Single
class MyComponent(val myDependency : MyDependency)

Koin Annotations keep the same semantic as the Koin DSL. You can declare your components with the following definitions:

• @Single - singleton instance (declared with single { } in DSL)
• @Factory - factory instance. For instances recreated each time you need an instance. (declared with factory { } in DSL)
• @KoinViewModel - Android ViewModel instance (declared with viewModel { } in DSL)

For Scopes, check the Declaring Scopes section.

Automatic or Specific Binding

When declaring a component, all detected "bindings" (associated supertypes) will be already prepared for you. For example, the following definition:

@Single
class MyComponent(val myDependency : MyDependency) : MyInterface

Koin will declare that your MyComponent component is also tied to MyInterface. The DSL equivalent is single { MyComponent(get()) } bind MyInterface::class.

Instead of letting Koin detect things for you, you can also specify what type you really want to bind with the binds annotation parameter:

@Single(binds = [MyBoundType::class])

Nullable Dependencies

If your component is using nullable dependency, don't worry it will be handled automatically for you. Keep using your definition annotation, and Koin will guess what to do:

@Single
class MyComponent(val myDependency : MyDependency?)

The generated DSL equivalent will be single { MyComponent(getOrNull()) }

Note that this also works for injected Parameters and properties

Qualifier with @Named

You can add a "name" to definition (also called qualifier), to make distinction between several definitions for the same type, with the @Named annotation:

@Single
@Named("InMemoryLogger")
class LoggerInMemoryDataSource : LoggerDataSource

@Single
@Named("DatabaseLogger")
class LoggerLocalDataSource(private val logDao: LogDao) : LoggerDataSource

When resolving a dependency, just use the qualifier with named function:

val logger: LoggerDataSource by inject(named("InMemoryLogger"))

Injected Parameters with @InjectedParam

You can tag a constructor member as "injected parameter", which means that the dependency will be passed in the graph when calling for resolution.

For example:

@Single
class MyComponent(@InjectedParam val myDependency : MyDependency)

Then you can call your MyComponent and pass a instance of MyDependency:

val m = MyDependency
// Resolve MyComponent while passing  MyDependency
koin.get<MyComponent> { parametersOf(m) }

The generated DSL equivalent will be single { params -> MyComponent(params.get()) }

Injecting a lazy dependency - Lazy<T>

Koin can automatically detect and resolve a lazy dependency. Here for example, we want to resolve lazily the LoggerDataSource definition. You just need to use the Lazy Kotlin type like follow:

@Single
class LoggerInMemoryDataSource : LoggerDataSource

@Single
class LoggerAggregator(val lazyLogger : Lazy<LoggerDataSource>)

Behind it will generate the DSL like with inject() instead of get():

single { LoggerAggregator(inject()) }

Injecting a list of dependencies - List<T>

Koin can automatically detect and resolve all a list of dependency. Here for example, we want to resolve all LoggerDataSource definition. You just need to use the List Kotlin type like follow:

@Single
@Named("InMemoryLogger")
class LoggerInMemoryDataSource : LoggerDataSource

@Single
@Named("DatabaseLogger")
class LoggerLocalDataSource(private val logDao: LogDao) : LoggerDataSource

@Single
class LoggerAggregator(val datasource : List<LoggerDataSource>)

Behind it will generate the DSL like with getAll() function:

single { LoggerAggregator(getAll()) }

Properties with @Property

To resolve a Koin property in your definition, just tag a constructor member with @Property. Ths is will resolve the Koin property thanks to the value passed to the annotation:

@Single
class MyComponent(@Property("my_key") val myProperty : String)

The generated DSL equivalent will be single { MyComponent(getProperty("my_key")) }