Gonna try implementing this later, might have errors

dagger-subcomponent-example.kt

// The primary component has the dependency graph for the authentication classes
// and the login activity

@Component(modules = [
    LoginModule::class, 
    AuthModule::class,
    LoggedInComponent.InstallModule::class
])
interface ApplicationComponent {
    val userLoggedInComponent: LoggedInComponent.Factory
    
    fun inject(activity: LoginActivity)
    
    @Component.Factory
    interface Factory {
        fun create(
            @BindsInstance appContext: Context
        )
    }
}

@Qualifier
@Retention(AnnotationRetention.RUNTIME)
annotation class UserEmail {}

// The logged in component extends the object graph with the YouTube classes

@Subcomponent(modules = [YouTubeModule::class])
interface LoggedInComponent {
    
    @Subcomponent.Factory
    interface Factory {
        // Allows me to receive the user email when extending the dependency graph
        fun create(
            @BindsInstance @UserEmail userEmail: String
        )   
    }
    
    @Module(subcomponents = [LoggedInComponent::class])
    interface InstallModule {}
}


class MyApp : Application() {
    val injector: ApplicationComponent by lazy {
        // Will instantiate the root dependency graph lazily
        DaggerApplicationComponent
            .factory()
            .create(appContext = this)
    }
}

class LoginActivity : AppCompatActivity() {
    @Inject private lateinit var authManager: AuthManager
    
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)  
        (application as MyApp).injector.inject(this)
        
        login_btn.onClickListener {
            val signInIntent = authManager.getSignInIntent()
            startActivityForResult(signInIntent, REQUEST_SIGN_IN)
        }
    }
    
    override fun onActivityResult(requestCode: Int, resultCode: Int, arguments: Bundle) {
        if (requestCode == REQUEST_SIGN_IN) {
            val result = authManager.processResultIntent(intent)
            when (result) {
                is Auth.Success -> {
                    val intent = Intent(this, YouTubeActivty::class.java).apply {
                        putExtra(USER_EMAIL, result.account.userEmail)   
                    }
                   startActivity(intent)
                }
                is Auth.Error -> {
                    /* Show snackbar */   
                }
            }
        }
    }
    
    companion object {   
        const val REQUEST_SIGN_IN = 1000
    }
}

class YouTubeActivity :  AppCompatActivity() {
    
    private lateinit var youtubeViewModel: YouTubeViewModel
 
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        // The Intent extras are delivered in both configuration changes and process death
        val email = intent.extras!!.get(USER_EMAIL)
        val loggedInInjector = (application as MyApp).injector
            .userLoggedInComponent
            .factory()
            .create(userEmail = email)
        
        // There's probably a better way to do this
        youtubeViewModel = ViewModelProvider(this, object: ViewModelProvider.Factory {
            override fun <T : ViewModel> create(modelClass: Class<T>): T = loggedInInjector.youtubeViewModel as T   
        }).get(YoutubeViewModel::class.java)     
    }
    
    // Do stuff with the ViewModel
}