안드로이드에서 Kotlin으로 recyclerView diffUtil 구현하기

notifyDataSetChanged()보다 더 효율적으로 작업하기 위한 DiffUtil() 클래스.

diffUtil class 만들기

DiffCallback.kt

    inner class DiffCallback(
        private var oldList: ArrayList<RecyclerViewItem>,
        private var newList: ArrayList<RecyclerViewItem>
    ): DiffUtil.Callback() {
        override fun getOldListSize(): Int = oldList.size

        override fun getNewListSize(): Int = newList.size

        override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
            return oldList[oldItemPosition] == newList[newItemPosition]
        }

        override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
            return oldList[oldItemPosition].id == newList[newItemPosition].id
        }

recyclerView adapter에서 diffUtil 사용하기

RecyclerViewAdapter.kt 에서 setData라는 함수를 통해 diffUtil 사용

package com.mj.recyclerview_sample

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.RecyclerView

class RecyclerViewAdapter(): RecyclerView.Adapter<RecyclerViewAdapter.RecyclerViewViewHolder>() {

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

    override fun onBindViewHolder(holder: RecyclerViewViewHolder, position: Int) {
        holder.bind(recyclerViewItems[position])
    }

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

    fun setData(newRecyclerViewItems: ArrayList<RecyclerViewItem>){
        println(newRecyclerViewItems.size)
        val diffCallback = DiffCallback(recyclerViewItems, newRecyclerViewItems)
        val diffResult = DiffUtil.calculateDiff(diffCallback)
        recyclerViewItems.clear()
        println(newRecyclerViewItems.size)
        recyclerViewItems.addAll(newRecyclerViewItems)
        diffResult.dispatchUpdatesTo(this)

    }

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

        private val title: TextView = itemView.findViewById(R.id.title)
        private val subtitle: TextView = itemView.findViewById(R.id.subtitle)

        fun bind(recyclerViewItem: RecyclerViewItem) {
            title.text = recyclerViewItem.title
            subtitle.text = recyclerViewItem.subtitle

            itemView.setOnClickListener { itemClick(recyclerViewItem) }
        }

    }
}

MainActivity.kt에서 diffUtil 사용해보기

package com.mj.recyclerview_sample

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Toast
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val recyclerViewItems: ArrayList<RecyclerViewItem> = ArrayList()
        recyclerViewItems.add(RecyclerViewItem(1, "title1", "subtitle1"))
        recyclerViewItems.add(RecyclerViewItem(2, "title2", "subtitle2"))
        recyclerViewItems.add(RecyclerViewItem(3, "title3", "subtitle3"))
        recyclerViewItems.add(RecyclerViewItem(4, "title4", "subtitle4"))
        recyclerViewItems.add(RecyclerViewItem(5, "title5", "subtitle5"))


        val recyclerView = findViewById<RecyclerView>(R.id.recyclerView)
        recyclerView.layoutManager = LinearLayoutManager(this)

        val adapter = RecyclerViewAdapter(recyclerViewItems) { recyclerViewItem ->
            Toast.makeText(this, "${recyclerViewItem.title} 클릭", Toast.LENGTH_SHORT).show()
        }

        recyclerView.adapter = adapter

        val newRecyclerViewItems: ArrayList<RecyclerViewItem> = ArrayList()
        newRecyclerViewItems.add(RecyclerViewItem(1, "title1", "subtitle1"))
        newRecyclerViewItems.add(RecyclerViewItem(2, "title2", "subtitle2"))
        newRecyclerViewItems.add(RecyclerViewItem(3, "title3", "subtitle3"))
        newRecyclerViewItems.add(RecyclerViewItem(4, "title4", "subtitle4"))
        newRecyclerViewItems.add(RecyclerViewItem(5, "title5", "subtitle5"))
        newRecyclerViewItems.add(RecyclerViewItem(6, "title6", "subtitle6"))
        newRecyclerViewItems.add(RecyclerViewItem(7, "title7", "subtitle7"))

        adapter.setData(newRecyclerViewItems)

    }
}