LifecycleOwner implemented RecyclerView ViewHolder & Adapter (concept design)

HowToUseActivity.kt

import android.os.Bundle
import android.util.Log
import android.view.ViewGroup
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import androidx.databinding.DataBindingUtil
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleObserver
import androidx.lifecycle.OnLifecycleEvent
import app.keima.android.recyclerviewsandbox.databinding.ActivityMainBinding

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = DataBindingUtil.setContentView(this, R.layout.activity_main)

        binding.recyclerView.apply {
            adapter = MyAdapter(
                arrayOf(
                    "A", "B", "C", "D",
                    "A", "B", "C", "D",
                    "A", "B", "C", "D",
                    "A", "B", "C", "D"
                )
            )
        }
    }
}

class MyAdapter(private val dataset: Array<String>) :
    LifecycleRecyclerAdapter<MyAdapter.MyViewHolder>() {

    class MyViewHolder(private val textView: TextView) : LifecycleViewHolder(textView) {
        private val observer = MyObserver()

        init {
            lifecycle.addObserver(observer)
        }

        fun bindData(data: String) {
            textView.text = data
            observer.data = data
        }
    }

    class MyObserver() : LifecycleObserver {
        var data: String = "?"

        @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
        fun onCreate() {
            Log.d("MyObserver", "appear: $data")
        }

        @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
        fun onDestroy() {
            Log.d("MyObserver", "disappear: $data")
        }
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
        return MyViewHolder(TextView(parent.context).apply {
            setPadding(8, 40, 8, 40)
        })
    }

    override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
        holder.bindData("${dataset[position]} $position")
    }

    override fun getItemCount() = dataset.size

}

Licenses.md

This gist snippet is Public Domain.

LifecycleRecyclerAdapter.kt

import androidx.recyclerview.widget.RecyclerView

abstract class LifecycleRecyclerAdapter<T : LifecycleViewHolder> : RecyclerView.Adapter<T>() {

  override fun onViewAttachedToWindow(holder: T) {
    super.onViewAttachedToWindow(holder)
    holder.onAppear()
  }

  override fun onViewDetachedFromWindow(holder: T) {
    super.onViewDetachedFromWindow(holder)
    holder.onDisappear()
  }

}

LifecycleViewHolder.kt

import android.view.View
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleOwner
import androidx.lifecycle.LifecycleRegistry
import androidx.recyclerview.widget.RecyclerView

abstract class LifecycleViewHolder(itemView: View) :
    RecyclerView.ViewHolder(itemView), LifecycleOwner {

    private val lifecycleRegistry = LifecycleRegistry(this)

    init {
        lifecycleRegistry.currentState = Lifecycle.State.INITIALIZED
    }

    fun onAppear() {
        lifecycleRegistry.currentState = Lifecycle.State.CREATED
    }

    fun onDisappear() {
        lifecycleRegistry.currentState = Lifecycle.State.DESTROYED
    }

    override fun getLifecycle(): Lifecycle {
        return lifecycleRegistry
    }

}

It will cause memory leak, when RecyclerView detach from window, the onViewDetachedFromWindow callback will not invoked.