Kotlin Error: Dagger does not support injection into private fields

Question

I use in kotlin activity ViewPager and I want in Kotlin Fragment use the dagger injection. I have got Error: Dagger does not support injection into private fields. In Java Fragment the dagger injection work. Why can i not inject dagger in kotlin faragment ?

in my kotlin activity

mPagerAdapter = object : FragmentPagerAdapter(supportFragmentManager) {          private val mFragments = arrayOf(KotlinFragment(), JavaFragment())         private val mFragmentNames = arrayOf(getString(R.string.cashdocuments), getString(R.string.action_absmysql))          override fun getItem(position: Int): Fragment {             return mFragments[position]         }          override fun getCount(): Int {             return mFragments.size         }          override fun getPageTitle(position: Int): CharSequence {             return mFragmentNames[position]         }     } 

my kotlin fragment

class KotlinFragment : Fragment()  {   @Inject internal var mSharedPreferences: SharedPreferences? = null  override fun onCreate(savedInstanceState: Bundle?) {     super.onCreate(savedInstanceState)      (activity.application as SamfantozziApp).dgaeacomponent().inject(this)  }  override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?,                           savedInstanceState: Bundle?): View? {     super.onCreateView(inflater, container, savedInstanceState)     val rootView = inflater!!.inflate(R.layout.activity_absserver, container, false)      return rootView }  } 

messages gradle build

Answer 1

You have mistake here:

    @Inject internal var mSharedPreferences: SharedPreferences? = null 

This looks like you added @Inject annotation to the KotlinFragment class

Please change it to this and it will work:

var mSharedPreferences: SharedPreferences? = null         @Inject set 

Here is the link to the documentation: https://kotlinlang.org/docs/reference/annotations.html

Answer 2

Accidentally I came across to my own answer and have to confess, that in fact it isn't working (at least for my use-case). Please consider Avilio's answer which worked for me also: substitute internal with lateinit.

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Old answer

Remove internal modifier. Dagger needs at least package-private access in order to access annotated field. In Kotlin internal modifier is not a substitution for Java's package-private access modifier.

For detailed explanation of differences between modifiers in Java and Kotlin refer to Fragmented podcast's episode #101 - "Learning Kotlin – visibility modifiers, internal modifier, modules", as well as the official docs.