Koin
- Kotlin course
- Advanced
- Lesson 37/83
- 5 min
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.
Practice Start Koin and print
Open a startKoin { } block. Print println("Koin ready").
Starter code
// Koin
// write here
import org.koin.core.context.startKoin
fun main() {
}Sample solution
fun main() {
startKoin {
}
println("Koin ready")
}Expected output
Koin ready
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is Koin used for?
- Dependency injection Correct answer
- Serializing JSON
- Making HTTP requests
- Database management
Explanation: Koin is a dependency injection (DI) library.
2 Complete the startKoin call
____ {
modules(appModule)
}startKoin {
modules(appModule)
}Explanation: startKoin opens the Koin application.
3 Match Koin parts
| Term | Meaning |
|---|---|
startKoin |
Startup |
module |
Module block |
single |
Singleton |
by inject |
Gets dependency |