Start Koin

What is Koin.dart?

Koin is pragmatic lightweight dependency injection framework for Dart developers. Written in pure Dart, using functional resolution as key concept. Koin.dart is a port of the original version written in Kotlin.

Start the container

Once you have declared your definitions within Koin modules, your are ready to start the Koin container.

The startKoin function

The startKoin function is the main entry point to launch Koin container. It need 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((app){
// declare used modules
app.module(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
important

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 not accessible anymore directly, as we need a component to manage different kind of context: KoinContextHandler

KoinContextHandler is responsible to register and give access to the underlying KoinContext. It's called by startKoin to register a new GlobalContext. This will allow us to register a different kind of context, in the perspective of Koin Multiplatform. KoinContextHandler is then ready once startKoin has finished.

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])

Koin context isolation

For SDK Makers, you can also work with Koin in a non global way: use Koin for the DI of your library and avoid any conflict by people using your library and Koin by isolating your context.

In a standard way, we can start Koin like that:

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

From this, we can use the KoinComponent as it: it will use the GlobalContext Koin instance.

But if we want to use an isolated Koin instance, you can just declare it like follow:

// create a KoinApplication
var myKoinApplication = koinApplication((app){
app.module(coffeeAppModule);
});

You will have to keep your myApp instance avilable in your library and pass it to your custom KoinComponent implementation:

// Get a Context for your Koin instance
class MyKoinContext {
static KoinApplication koinApp;
}
// Register the Koin context with the KoinApplication
MyKoinContext.koinApp = myKoinApplication
abstract class CustomKoinComponent extends KoinComponent {
// Override default Koin instance, intially target on GlobalContext to yours
@override
Koin getKoin() => MyKoinContext.koinApp.koin;
}

And now, you register your context and run your own isolated Koin components:

// Register the Koin context
MyKoinContext.koinApp = myKoinApplication
class ACustomKoinComponent extends CustomKoinComponent{
// inject & get will target MyKoinContext
}

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()