Dagger2 inject a presenter into a Kotlin Activity error

Question

I use dragger2 to inject a presenter into a Kotlin Activity, the presenter is null,here is my code:

class CategoryDetailActivity : MvpActivity<ProductFilterView,ProductFilterPresenter>(), ProductFilterView {
private lateinit var presenter: ProductFilterPresenter
    @Inject set       


 override fun onCreate(savedInstanceState: Bundle?) {
        initialInjector()
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_category_detail)
        initData()
        initEvent()
    }
private fun initialInjector() {
    DaggerProductFilterComponent.builder()
            .applicationComponent(applicationComponent)
            .productFilterModule(ProductFilterModule())
            .build()
            .inject(this)
}
override fun getPresenter(): ProductFilterPresenter {
    return presenter!!
}

}

The method getPresenter() be called in MvpActivity's onCreate() ,and the MvpActivity is a java class. Initial the presenter need some instance provide by ProductFilterModule,Maybe presenter should be initial after Component injected,i guess. when I run ,it throw KotlinNullPointerException,the presenter is Null.

time: FATAL EXCEPTION: main
                                                                       Process: com.chiquedoll.chiquedoll, PID: 10617
                                                                       java.lang.RuntimeException: Unable to start activity ComponentInfo{com.chiquedoll.chiquedoll/com.chiquedoll.chiquedoll.view.activity.CategoryDetailActivity}: kotlin.KotlinNullPointerException
                                                                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                                           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                                           at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                           at android.os.Looper.loop(Looper.java:148)
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                           at java.lang.reflect.Method.invoke(Native Method)
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                        Caused by: kotlin.KotlinNullPointerException
                                                                           at com.chiquedoll.chiquedoll.view.activity.CategoryDetailActivity.getPresenter(CategoryDetailActivity.kt:281)
                                                                           at com.chiquedoll.chiquedoll.view.activity.CategoryDetailActivity.getPresenter(CategoryDetailActivity.kt:36)
                                                                           at com.chiquedoll.chiquedoll.view.activity.MvpActivity.onCreate(MvpActivity.java:19)
                                                                           at com.chiquedoll.chiquedoll.view.activity.CategoryDetailActivity.onCreate(CategoryDetailActivity.kt:65)
                                                                           at android.app.Activity.performCreate(Activity.java:6237)

If i use java to do it,it no problem.

Answer 1

Dagger 2 doesn't use setters to inject fields, it assigns values directly. Hence, correct version would be:

@Inject internal lateinit var presenter: ProductFilterPresenter

Note that Dagger 2 requires injectable fields to be at least internal , private won't work.