I can't reach any class member from a nested class in Kotlin

Question

I want to access a member of the MainFragment class from PersonAdapter class but none of them are available. I tried making both the classes and the members public and private also but so far nothing worked. I guess I'm missing something obvious but I just can't figure it out.

class MainFragment : Fragment() {
    lateinit var personAdapter: PersonAdapter
    lateinit var personListener: OnPersonSelected
    private var realm: Realm by Delegates.notNull()
    lateinit var realmListener: RealmChangeListener<Realm>

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        val v = inflater.inflate(R.layout.fragment_main, container, false)
        return v
    }

    class PersonAdapter() : RecyclerView.Adapter<ViewHolder>() {
        var localPersonList = personList

        override fun onBindViewHolder(holder: ViewHolder, position: Int) {
            holder.bindItems(localPersonList[position])

            holder.itemView.setOnClickListener {
                Toast.makeText(context, "click", Toast.LENGTH_SHORT).show()
                //I want to reach personListener from here
            }
        }

        override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int): ViewHolder {
            val v = LayoutInflater.from(parent!!.context).inflate(R.layout.person_list_item, parent, false)
            return ViewHolder(v)
        }
    }}

Answer 1

In Kotlin, nested classes cannot access the outer class instance by default, just like nested static classes can't in Java.

To do that, add the inner modifier to the nested class:

class MainFragment : Fragment() {
    // ...

    inner class PersonAdapter() : RecyclerView.Adapter<ViewHolder>() {
        // ...
    }
}

Note that an inner class holds a reference to its containing class instance, which may affect the lifetime of the latter and potentially lead to a memory leak if the inner class instance is stored globally.

See: Nested classes in the language reference