How to use Koin in multiple module?

Question

There are two modules in my android project, app module and lib module.

Both these two modules need Koin for D.I., so I call startKoin in MyApplication class in app module, and IninKointContentProvider in lib module as below.

// app module
class MyApplication : Application() {
    override fun onCreate() {
        super.onCreate()
        startKoin(this, modules1)
    }
}

// lib module
class InitKoinContentProvider : ContentProvider() {
    override fun onCreate(): Boolean {
        startKoin(context.applicationContext, modules2)
        return true
    }
}

Then app crashed and shown this message

Caused by: org.koin.error.BeanOverrideException: Try to override definition with Single [class='android.content.Context'], but override is not allowed. Use 'override' option in your definition or module.

I guess startKoin can be called only one time.

The solution I found is merging two koin modules then calling startKoin in MyApplication, but I don't like it. Lib module may be imported by other android project which doesn't use koin, in that case, I think calling startKoin in InitKoinContentProvider is better.

Any solution for this problem?? Thanks!

Answer 1

I found the best solution inspired by @laalto's answer, thanks!

Upgrade to koin 2.0, then use KoinApplication and customized KoinComponent to create a isolated koin context, it can let lib module using koin without any initializing call by app module, still start koin in ContentProvider. The whole code may like below.

// app module
class MyApplication : Application() {
    override fun onCreate() {
        super.onCreate()
        startKoin {
            androidContext(this@MyApplication)
            modules(module{
                viewModel { MainViewModel() }
            })
        }
    }
}

class MainActivity: AppCompactActivity() {
    private val viewModel: MainViewModel by viewModel()
}



// lib module
internal object MyKoinContext {
    lateinit var koinApplication: KoinApplication
}

interface MyKoinComponent : KoinComponent {
    override fun getKoin(): Koin {
        return MyKoinContext.koinApplication.koin
    }
}

class InitKoinContentProvider : ContentProvider() {
    override fun onCreate(): Boolean {
        MyKoinContext.koinApplication = koinApplication {
            androidContext(context.applicationContext)
            modules(module{
                viewModel { FooViewModel() }
            })
        }
        return true
    }
}

class FooActivity: AppCompactActivity(), MyKoinComponent {
    private val viewModel: FooViewModel by viewModel()
}

Ref: https://insert-koin.io/docs/2.0/documentation/reference/index.html#_koin_context_isolation