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Start Koin

Koin is a DSL, a lightweight container and a pragmatic API. Once you have declared your definitions within Koin modules, you are ready to start the Koin container.

The startKoin function​

The startKoin function is the main entry point to launch Koin container. It needs a list of Koin modules to run. Modules are loaded and definitions are ready to be resolved by the Koin container.

.Starting Koin

// start a KoinApplication in Global context
startKoin {
    // declare used modules
    modules(coffeeAppModule)
}

Once startKoin has been called, Koin will read all your modules & definitions. Koin is then ready for any get() or by inject() call to retrieve the needed instance.

Your Koin container can have several options:

  • logger - to enable logging - see <<logging.adoc#_logging,logging>> section
  • properties(), fileProperties( ) or environmentProperties( ) to load properties from environment, koin.properties file, extra properties ... - see <<properties.adoc#_lproperties,properties>> section
info

The startKoin can't be called more than once. If you need several point to load modules, use the loadKoinModules function.

Behind the start - Koin instance under the hood​

When we start Koin, we create a KoinApplication instance that represents the Koin container configuration instance. Once launched, it will produce a Koin instance resulting of your modules and options. This Koin instance is then hold by the GlobalContext, to be used by any KoinComponent class.

The GlobalContext is a default JVM context strategy for Koin. It's called by startKoin and register to GlobalContext. This will allow us to register a different kind of context, in the perspective of Koin Multiplatform.

Loading modules after startKoin​

You can't call the startKoin function more than once. But you can use directly the loadKoinModules() functions.

This function is interesting for SDK makers who want to use Koin, because they don't need to use the starKoin() function and just use the loadKoinModules at the start of their library.

loadKoinModules(module1,module2 ...)

Unloading modules​

it's possible also to unload a bunch of definition, and then release theirs instance with the given function:

unloadKoinModules(module1,module2 ...)

Stop Koin - closing all resources​

You can close all the Koin resources and drop instances & definitions. For this you can use the stopKoin() function from anywhere, to stop the Koin GlobalContext. Else on a KoinApplication instance, just call close()

Logging​

Koin has a simple logging API to log any Koin activity (allocation, lookup ...). The logging API is represented by the class below:

Koin Logger

abstract class Logger(var level: Level = Level.INFO) {

    abstract fun log(level: Level, msg: MESSAGE)

    fun debug(msg: MESSAGE) {
        log(Level.DEBUG, msg)
    }

    fun info(msg: MESSAGE) {
        log(Level.INFO, msg)
    }

    fun error(msg: MESSAGE) {
        log(Level.ERROR, msg)
    }
}

Koin proposes some implementation of logging, in function of the target platform:

  • PrintLogger - directly log into console (included in koin-core)
  • EmptyLogger - log nothing (included in koin-core)
  • SLF4JLogger - Log with SLF4J. Used by ktor and spark (koin-logger-slf4j project)
  • AndroidLogger - log into Android Logger (included in koin-android)

Set logging at start​

By default, By default Koin use the EmptyLogger. You can use directly the PrintLogger as following:

startKoin {
    logger(LEVEL.INFO)
}

Loading properties​

You can load several type of properties at start:

  • environment properties - load system properties
  • koin.properties file - load properties from /src/main/resources/koin.properties file
  • "extra" start properties - map of values passed at startKoin function

Read property from a module​

Be sure to load properties at Koin start:

startKoin {
    // Load properties from the default location
    // (i.e. `/src/main/resources/koin.properties`)
    fileProperties()
}

In a Koin module, you can get a property by its key:

in /src/main/resources/koin.properties file

// Key - value
server_url=http://service_url

Just load it with getProperty function:

val myModule = module {

    // use the "server_url" key to retrieve its value
    single { MyService(getProperty("server_url")) }
}