Dagger 2, Providing Application Context in Module

Question

Im pretty new in Android development and newer in DI. I am using Kotlin on a personal project where I am experimenting with Dagger 2. I managed to set it up for a util class, but where i need to have a context to use it to inject a class that requires a context (a sharedpref manager class), I failed. Here is my code, and here is the error ( NPE ) i am getting. Thank you in advance.

my module class

package com.android.pine

import android.content.Context
import com.android.pine.utils.SharedPreferencesManager
import dagger.Module
import dagger.Provides
import javax.inject.Singleton

@Module
class AppModule {

    @Provides
    @Singleton
    fun context(pineApplication: PineApplication): Context = pineApplication.applicationContext

    @Provides
    @Singleton
    fun provideSharedPrefManager(context: Context): SharedPreferencesManager = SharedPreferencesManager(context)
}

my component class:

package com.android.pine

import com.android.pine.home.HomePresenter
import com.android.pine.home.categories.CategoryAdapter
import dagger.Component
import javax.inject.Singleton

@Singleton
@Component(modules = arrayOf(AppModule::class))
interface AppComponent {
    fun inject(categoryAdapter: CategoryAdapter)
    fun inject(homePresenter: HomePresenter)
}

edit: added the info below, How I call the inject of sharedPreferencesManager:

class HomePresenter : BasePresenter<HomeView>() {

    @Inject
    lateinit var sharedPreferencesManager: SharedPreferencesManager
.
.
.

Also in my HomePresenter class, in onAttached method override:

 DaggerAppComponent.create().inject(this)

My pineApplication class and SharedPrefManager class looks like this:

class PineApplication @Inject constructor(): Application()

SharedPref:

class SharedPreferencesManager @Inject constructor(context: Context) {
.
.
.

Crash, can not get the pineApplication.getContext() (edited, added the full stack trace)

     06-02 11:57:01.028 14840-14840/com.android.pine.debug E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.android.pine.debug, PID: 14840
java.lang.RuntimeException: Unable to resume activity {com.android.pine.debug/com.android.pine.home.HomeActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3429)
    at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3469)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2732)
    at android.app.ActivityThread.-wrap12(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6119)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
    at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:106)
    at com.android.pine.AppModule.context(AppModule.kt:12)
    at com.android.pine.AppModule_ContextFactory.proxyContext(AppModule_ContextFactory.java:34)
    at com.android.pine.DaggerAppComponent.getContext(DaggerAppComponent.java:29)
    at com.android.pine.DaggerAppComponent.getSharedPreferencesManager(DaggerAppComponent.java:34)
    at com.android.pine.DaggerAppComponent.injectHomePresenter(DaggerAppComponent.java:59)
    at com.android.pine.DaggerAppComponent.inject(DaggerAppComponent.java:49)
    at com.android.pine.home.HomePresenter.onAttached(HomePresenter.kt:31)
    at com.android.pine.home.HomePresenter.onAttached(HomePresenter.kt:10)
    at com.android.pine.core.BaseActivity.onResume(BaseActivity.kt:34)
    at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1269)
    at android.app.Activity.performResume(Activity.java:6783)
    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3406)
    at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3469) 
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2732) 
    at android.app.ActivityThread.-wrap12(ActivityThread.java) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:154) 
    at android.app.ActivityThread.main(ActivityThread.java:6119) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 

Answer 1

This is how It is done. Using @BindsInstance in your component will inject application to all of your modules.In your case just to AppModule

@Singleton
@Component(modules = arrayOf(AppModule::class))
interface AppComponent {
    @Component.Builder
    interface Builder() {
        fun build(): AppComponent

        @BindsInstance
        fun application(application: Application): Builder
    }
}

** Delete code to "Provides application" function in your APP module and make sure you pass application context to create sharedPreferences.

@Module
class AppModule {


@Provides
@Singleton
fun provideSharedPrefManager(context: Application): SharedPreferencesManager = 
    SharedPreferencesManager(context)
}

and now in your onCreate of applicationClass

DaggerAppComponent.builder().application(this).build()

Optional: if you want to inject something into your applicationClass then do the following

 DaggerAppComponent.builder().application(this).build().inject(this)

Answer 2

You can't use class PineApplication @Inject constructor(): Application() to create PineApplication. It's a framework class and has to be created by the Android Framework.

Doing so Dagger will create PineApplication, but applicationContext will return null as it has never been initialized (by the system).

Don't use constructor injection for framework classes and don't create the yourself. Use @Bindsintance to add the object to the component with its builder, or use a module to provide it.