Version: 3.2

Koin Annotations

The goal of Koin Annotations project is to help declare Koin definition in a very fast and intuitive way, and generate all underlying Koin DSL for you. The goal is to help developer experience to scale and go fast ๐Ÿš€, thanks to Kotlin Compilers.

Getting Started

Not familiar with Koin? First take a look at Koin Getting Started

Tag your cpomnents with definition & module annotations, and use the regular Koin API.

// Tag your component to declare a definition
@Single
class MyComponent
// Declare a module and scan for annotations
@Module
@ComponentScan
class MyModule

Use the org.koin.ksp.generated.* import as follow to be able to use generated code:

// Use Koin Generation
import org.koin.ksp.generated.*
fun main() {
val koin = startKoin {
printLogger()
modules(
// use your modules here, with generated ".module" extension on Module classes
MyModule().module
)
}
// Just use your Koin API as regular
koin.get<MyComponent>()
}

That's it, you can use your new definitions in Koin with the regular Koin API

Definitions

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 annotatation, 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 thigns 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 depndency, don't worry it will be handled automaticaly for you. Keep using yopur 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()) }

Properties with @Property

To resolve a Koin property in your definition, just tag a cosntructor 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")) }

Declaring Scopes with @Scope

You can declare definition inside a scope, by using the @Scope annotation. The target scope can be specified as a class, or a name:

// scope by type
@Scope(MyScope::class)
class MyComponent
// scope by name
@Scope(name = "MyScopeName")
class MyComponent

The generated DSL equivalent will be:

scope<MyScope> {
scoped { MyComponent() }
}
// or
scope(named("MyScopeName")) {
scoped { MyComponent() }
}

You can cumulate @Factory or @KoinViewModel, to specify a scoped Factory or a ViewModel. Also you can use the @Scoped annotation to let define specific bindings on a @Scope tagged components.


Modules

While using definitions, you may need to organize them in modules or not. You can even not use any module at all and use the "default" generated module.

No Module - Using the Generated Default Module

If you don't want to specify any module, Koin provide a default one to host all your definitions. The defaultModule is ready to be use directly:

// Use Koin Generation
import org.koin.ksp.generated.*
fun main() {
startKoin {
defaultModule()
}
}
// or
fun main() {
startKoin {
modules(
defaultModule
)
}
}

Don't forget to use the org.koin.ksp.generated.* import

Class Module with @Module

To declare a module, just tag a class with @Module annotation:

@Module
class MyModule

To load your module in Koin, just use the .module extension generated for any @Module class. Just create new instance of your module MyModule().module:

// Use Koin Generation
import org.koin.ksp.generated.*
fun main() {
startKoin {
modules(
MyModule().module
)
}
}

Don't forget to use the org.koin.ksp.generated.* import

Components Scan with @ComponentScan

To scan and gather annotated components into a module, just use the @ComponentScan annotation on a module:

@Module
@ComponentScan
class MyModule

This will scan current package and subpackages for annotated components.

You can specify to scan a given package @ComponentScan("com.my.package")

Definitions in Class Modules

To define a definition directly in your can, you an annotate a function with definition annotations:

// given
// class MyComponent(val myDependency : MyDependency)
@Module
class MyModule {
@Single
fun myComponent(myDependency : MyDependency) = MyComponent(myDependency)
}

@InjectedParam, @Property are also usable on function members

Including Modules

To include other class modules to your module, just use the includes attribute of the @Module annotation:

@Module
class ModuleA
@Module(includes = [ModuleA::class])
class ModuleB

This way you can just run your root module:

// Use Koin Generation
import org.koin.ksp.generated.*
fun main() {
startKoin {
modules(
// will load ModuleB & ModuleA
ModuleB().module
)
}
}