Dagger2 not inject

Question

I am a newbie to android and trying to use Dagger2. I spend whole night and still dont know why my dagger does not provide presenter. Here are my code (I use Kotlin)

AppComponent

@Singleton
@Component(modules = arrayOf(PresenterModule::class))
interface AppComponent {

    fun inject(target: SplashActivity)

}

PresenterModule

@Module
class PresenterModule {

    @Provides
    @Singleton
    fun provideSplashPresenter(): SplashPresenter {
        return SplashPresenter()
    }
}

App

class App: Application() {

    companion object {
        lateinit var appComponent: AppComponent
    }

    override fun onCreate() {
        super.onCreate()
        appComponent = initDagger()
    }

    private fun initDagger(): AppComponent {
        return DaggerAppComponent.create()
    }
}

This is the presenter

class SplashPresenter: BasePresenterImpl<SplashContract.View>(), SplashContract.Presenter {

    override fun performToast(mess: String) {
        logi("abc", "performToast")
        logi("abc", "mess: " + mess)
        mView?.showLoading()
        if (mess.isNullOrBlank()) {
            mView?.showTosat("this is empty mess") ?: logi("abc", "null")
        } else {
            mView?.showTosat(mess) ?: logi("abc", "null")
        }
        mView?.hideLoading()

    }
}

And finally, this is my SplashActivity

class SplashActivity : BaseActivity(), SplashContract.View {


    @Inject
    lateinit var presenter: SplashPresenter

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_splash)

        presenter.attachView(this)

        //TODO: check log in
        //TODO: If logged in => start main screen
        //TODO: If not logged in => load login activity

        button.setOnClickListener{
            presenter.performToast(editText.text.toString())
            logi("abc", "perform clicked")
        }
    }
}

When I run these code, I got this error Lateinit property presenter has not been initialized, which means that "Inject" does not work

Answer 1

Since you're not using constructor injection here (which you can't, because you don't 'own' the activity's constructor) Dagger does not 'know' that it has to inject something into your Activity . You have to manually inject like this:

(applicationContext as App).appComponent.inject(this) 

in your SplashActivity 's onCreate() method (before using the presenter, of course).

Second, your presenter needs a constructor that tells Dagger how to construct/'build' the presenter, which means a constructor annotated with the @Inject annotation, so:

class SplashPresenter @Inject constructor(): BasePresenterImpl<SplashContract.View>(), SplashContract.Presenter 

Answer 2

You forgot to inject the SplashActivity:

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    App.appComponent.inject(this)
    setContentView(R.layout.activity_splash)
    ...