A simple SystemServiceLocator that enables to easy customization of Context `getSystemService`.

Example.kt

class MainApplication : Application() {

    private val component = MainComponent.Factory.create(application = this)

    private val locator = SystemServiceLocator {
        register { component.getFragmentFactory() }
    }

    override fun getSystemService(name: String): Any? {
        return locator.getSystemService(name) ?: super.getSystemService(name)
    }

    override fun getSystemServiceName(serviceClass: Class<*>): String? {
        return locator.getSystemServiceName(serviceClass)
            ?: super.getSystemServiceName(serviceClass)
    }
}

class MainApplication : Application() {
    private val component = MainComponent.Factory.create(application = this)

    private val locator = SystemServiceLocator {
        register { component.getNavigationChannel() }
        register { component.getFragmentFactory() }
    }

    override fun getSystemService(name: String): Any? {
        return locator.getSystemService(name) ?: super.getSystemService(name)
    }

    override fun getSystemServiceName(serviceClass: Class<*>): String? {
        return locator.getSystemServiceName(serviceClass)
            ?: super.getSystemServiceName(serviceClass)
    }
}

class MainActivity : FragmentHostActivity(HomeFragment::class) {

    override fun onCreate(savedInstanceState: Bundle?) {
        supportFragmentManager.fragmentFactory = application.getSystemService()!!
        super.onCreate(savedInstanceState)
    }
}

SystemServiceLocator.kt

class SystemServiceLocator(
    private val serviceInstanceMap: Map<String, () -> Any>,
    private val serviceNameMap: Map<Class<*>, String>,
) {

    fun getSystemService(name: String): Any? = serviceInstanceMap[name]?.invoke()

    fun getSystemServiceName(serviceClass: Class<*>): String? = serviceNameMap[serviceClass]
}

fun SystemServiceLocator(block: SystemServiceRegistry.() -> Unit): SystemServiceLocator {
    val registry = SystemServiceRegistry().apply(block)
    return SystemServiceLocator(registry.serviceInstanceMap, registry.serviceNameMap)
}

class SystemServiceRegistry {

    @PublishedApi
    internal val serviceInstanceMap = mutableMapOf<String, () -> Any>()

    @PublishedApi
    internal val serviceNameMap = mutableMapOf<Class<*>, String>()

    inline fun <reified T : Any> register(noinline getService: () -> T) {
        val name = T::class.java.simpleName
        serviceInstanceMap[name] = getService
        serviceNameMap[T::class.java] = name
    }
}