无法从内部类访问变量：Kotlin android

I am new to Kotlin development in android. here I am trying to access a variable defined in a class from it's inner class as below.

class MainActivity : AppCompatActivity() {

    var frags: MutableList<Fragment> = mutableListOf()

//.............onCreate and other methods ....

    internal class CustAdapter(var arrayList: ArrayList<NavigationData>) : RecyclerView.Adapter<CustAdapter.MyViewHolder>() {
    override fun onBindViewHolder(holder: MyViewHolder?, position: Int) {
        holder!!.bindItems(arrayList[position])
    }

    override fun getItemCount(): Int {
        return arrayList.size
    }
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CustAdapter.MyViewHolder {
        val v = LayoutInflater.from(parent.context).inflate(R.layout.navigation_item, parent, false)
        return MyViewHolder(v)
    }

    class MyViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        fun bindItems(data: NavigationData) {


            itemView.setOnClickListener {
                   frags.add(BoardFrag()) ///// here i'm getting error "unresolved symbol"

            }
        }
    }
}    
}

在内部类MyViewHolder中，它不允许我访问外部范围的任何变量.

即使我也无法访问从 import kotlinx.android.synthetic.main.activity_main.*个内部类方法导入的视图ID.

I was able to access variables in such a way in java but i have read many question on stackoverflow but i didn't get answer yet.