如何在 Kotlin 的内部 class 中使用外部 class 的属性？

Question

I have this class:

class ItemsAdapter(
    val items: List<Item> = mutableListOf()
) {
    class ItemViewHolder(private val itemView: View) : ViewHolder(itemView), View.OnClickListener {
        override fun onClick(v: View) {
            val clickedItem = items.get(adapterPosition)
        }
    }
}

Even if items object is defined in the outer class, it cannot be used in the inner class. How can I use the items object in the onClick function?

Answer 1

You need to mark ItemViewHolder as an inner class

inner class ItemViewHolder

More info on https://kotlinlang.org/docs/reference/nested-classes.html

Answer 2

Just use inner Keyword

import android.view.View
import androidx.recyclerview.widget.RecyclerView

class ItemsAdapter(
    val items: List<Item> = mutableListOf()
) {
    inner class ItemViewHolder(private val itemView: View) : RecyclerView.ViewHolder(itemView), View.OnClickListener {
        override fun onClick(v: View) {
            val clickedItem = items.get(adapterPosition)
        }
    }
}

Answer 3

If you want to access the members of an outer class in the inner class, then you have to mark the inner class with inner keyword.

Mark your ItemViewHolder as inner and everything should work fine.

class ItemsAdapter(
    val items: List<Item> = mutableListOf()
) {
    inner class ItemViewHolder(private val itemView: View) : ViewHolder(itemView), View.OnClickListener {
        override fun onClick(v: View) {
            val clickedItem = items.get(adapterPosition)
        }
    }
}