How can I define a property that returns the curre

The Code B is a customized RecyclerView.Adapter with RadioButton.

I hope to get the current selected index of the RadioButton, so I add a property mySelectedIndex in Code A, but mySelectedIndex will not change after it's called fro the first time.

How can I do this? Thanks!

And more,

private lateinit var selectedIndex= mCustomAdapter.getSelectedIndex() will not work too!

Code A

private lateinit var mCustomAdapter: CustomAdapter

private val mySelectedIndex by lazy {
        mCustomAdapter.getSelectedIndex()
}


private fun a(){
  backup(mySelectedIndex)
}


private fun b(){
  restore(mySelectedIndex) 
}

Code B

class CustomAdapter (val backupItemList: List<MSetting>) : RecyclerView.Adapter<CustomAdapter.ViewHolder>() {

    val noRecord=-1
    private var mSelectedIndex = noRecord

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

    fun getSelectedIndex():Int{
        return  mSelectedIndex
    }

    fun setSelectedIndex(index:Int){
        if (index in 0..(backupItemList.size-1) ){
            mSelectedIndex=index
        }
        notifyDataSetChanged();
    }

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

    override fun getItemCount(): Int {
        return backupItemList.size
    }

    inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {

        fun bindItems(aMSetting: MSetting) {          

            itemView.radioButton.setOnClickListener {
                mSelectedIndex=adapterPosition
                notifyDataSetChanged();
            }

            if(adapterPosition == 0 && mSelectedIndex == noRecord) {            
                itemView.radioButton.isChecked = true
                mSelectedIndex=adapterPosition
            }
            else {
                itemView.radioButton.isChecked =(adapterPosition == mSelectedIndex)
            }
        }

    }

}

回答1:

By using the by lazy delegation here you're making sure that the same value will be returned after the first initialization of mySelectedIndex.

You might want to omit the delegation and do something like this instead:

private val mySelectedIndex
    get () = mCustomAdapter.getSelectedIndex()

As a side note, this snippet above is not equal to the following:

private val mySelectedIndex
    get () = {
        mCustomAdapter.getSelectedIndex()
    }

The latter will return a function reference to getSelectedIndex() while the former will return its result.

回答2:

Replace

private val mySelectedIndex by lazy {
    mCustomAdapter.getSelectedIndex()
}

with

private val mySelectedIndex get () {
    return mCustomAdapter.getSelectedIndex()
}

private val mySelectedIndex get () =
    mCustomAdapter.getSelectedIndex()

should work.