Koin

Learn the Koin DI framework.

What is Koin?

Koin is a lightweight dependency injection (DI) library for Kotlin. It is written with a Kotlin DSL; it uses no reflection and offers compile time type safety.

An app starts with startKoin { modules(appModule) }. Modules are declared with a module { ... } block; dependencies are provided with single or factory. Classes get their dependencies with by inject(). Koin needs no annotation processor like Dagger; setup is simple. In this lesson you will set up the basic startup flow.

Starting Koin

To start Koin you call startKoin { modules(appModule) }. This call builds a KoinApplication.

Example: startKoin { modules(appModule) }. The modules function lists the modules the app will use. Multiple modules are allowed: modules(module1, module2). The startKoin call happens once at app start; on Android it is common in Application.onCreate. Without starting Koin, by inject() does not work.

Exercise Start Koin and print

Open a startKoin { } block. Print println("Koin ready").

Show example solution

fun main() {
    startKoin {
    }
    println("Koin ready")
}

Test yourself

What is Koin used for?
- Dependency injection
- Serializing JSON
- Making HTTP requests
- Database management
Show answer

Dependency injection — Koin is a dependency injection (DI) library.

Complete the startKoin call

____ {
    modules(appModule)
}

Show answer

startKoin {
    modules(appModule)
}

Match Koin parts

startKoin

Startup
module

Module block
single

Singleton
by inject

Gets dependency

Next lesson: module

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