How to Improve RecyclerView Performance in Android Using DiffUtil?
DiffUtil class is used to improve the performance of RecyclerView. The algorithm behind DiffUtil is that it takes two lists and finds differences between the two and provides the updated list as an output. It uses Eugene W. Myers’s difference algorithm to calculate the minimal number of updates. In this article, we will see its implementations. Note that we are going to implement this project using the Kotlin language.
Step by Step Implementation
Step 1: Create a new project
To create a new project in Android Studio please refer to How to Create/Start a New Project in Android Studio. Note that select Kotlin as the programming language.
Step 2: Add view binding dependency
Go to build.gradle(app) and the following dependency inside the android tag and click sync now.
buildFeatures {
viewBinding true
}
Step 3: Create a new model class
Create a new class Language.kt we will use data of custom generic “Language” to pass in the list that will be shown in RecyclerView.
Kotlin
// this is the Language model class class Language( val id : Int = 0 , val name : String = "" , val exp : String = "" ) |
Step 4: Create a new layout file and name it the single_item.xml file
Go to the single_item.xml file and refer to the following code. Below is the code for the single_item.xml file. It is the single item layout that we will use in RecyclerView.
XML
<? xml version = "1.0" encoding = "utf-8" ?> < com.google.android.material.card.MaterialCardView xmlns:android = "http://schemas.android.com/apk/res/android" xmlns:app = "http://schemas.android.com/apk/res-auto" android:layout_width = "match_parent" android:layout_marginBottom = "10dp" android:layout_marginStart = "5dp" android:layout_marginEnd = "5dp" android:layout_height = "110dp" > < androidx.constraintlayout.widget.ConstraintLayout android:layout_width = "match_parent" android:layout_height = "match_parent" > <!--Add image view, We will not set any data here.--> < ImageView android:id = "@+id/iv_language" android:layout_width = "80dp" android:layout_height = "90dp" android:layout_marginStart = "20dp" android:layout_marginTop = "10dp" android:scaleType = "fitCenter" android:src = "@mipmap/ic_launcher" app:layout_constraintLeft_toLeftOf = "parent" app:layout_constraintTop_toTopOf = "parent" /> <!--Text view for showing the language name--> < TextView android:id = "@+id/tv_lang_name" android:layout_width = "wrap_content" android:layout_height = "wrap_content" android:layout_marginStart = "30dp" android:layout_marginTop = "30dp" android:text = "Language" android:textSize = "16sp" android:textStyle = "bold" app:layout_constraintLeft_toRightOf = "@id/iv_language" app:layout_constraintTop_toTopOf = "parent" /> <!--Text View for showing the exp--> < TextView android:id = "@+id/tv_exp" android:layout_width = "wrap_content" android:layout_height = "wrap_content" android:layout_marginTop = "10dp" android:text = "Exp : 3 years" app:layout_constraintLeft_toLeftOf = "@id/tv_lang_name" app:layout_constraintTop_toBottomOf = "@id/tv_lang_name" /> </ androidx.constraintlayout.widget.ConstraintLayout > </ com.google.android.material.card.MaterialCardView > |
Step 5: Working with the activity_main.xml
Go to the activity_main.xml file and refer to the following code. Below is the code for the activity_main.xml file. It has only a single RecyclerView which we will use to show our data.
XML
<? xml version = "1.0" encoding = "utf-8" ?> < androidx.constraintlayout.widget.ConstraintLayout xmlns:android = "http://schemas.android.com/apk/res/android" xmlns:app = "http://schemas.android.com/apk/res-auto" xmlns:tools = "http://schemas.android.com/tools" android:layout_width = "match_parent" android:background = "#F5F8FD" android:layout_height = "match_parent" tools:context = ".MainActivity" > <!--Add recycler view to main activity--> < androidx.recyclerview.widget.RecyclerView android:id = "@+id/rv_list" android:layout_width = "match_parent" android:layout_height = "match_parent" tools:listitem = "@layout/single_item" app:layoutManager = "androidx.recyclerview.widget.LinearLayoutManager" /> < com.google.android.material.floatingactionbutton.ExtendedFloatingActionButton android:id = "@+id/btn_new_language" android:layout_width = "wrap_content" android:layout_height = "wrap_content" android:text = "Add New Language" android:padding = "10dp" app:layout_constraintBottom_toBottomOf = "parent" app:layout_constraintRight_toRightOf = "parent" app:layout_constraintLeft_toLeftOf = "parent" android:layout_marginBottom = "20dp" /> </ androidx.constraintlayout.widget.ConstraintLayout > |
Step 6: Create a new class and name it MyDiffUtil.kt
Go to MyDiffUtil.kt file and write the following code. Comments are added for a better understanding of the code.
Kotlin
import androidx.recyclerview.widget.DiffUtil // pass two list one oldList and second newList class MyDiffUtil( private val oldList : List<Language>, private val newList : List<Language> ) :DiffUtil.Callback() { // implement methods override fun getOldListSize(): Int { // return oldList size return oldList.size } override fun getNewListSize(): Int { // return newList size return newList.size } override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean { // compare items based on their unique id return oldList[oldItemPosition].id == newList[newItemPosition].id } override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean { // in here compare each item if they are same or different // return false if any data is same else return true return when{ oldList[oldItemPosition].id != newList[newItemPosition].id -> false oldList[oldItemPosition].name != newList[newItemPosition].name -> false oldList[oldItemPosition].exp != newList[newItemPosition].exp -> false else -> true } } } |
Step 7: Working with the Adapter class
Create a new class RvAdapter.kt this will act as an Adapter class for the recycler view. Using View binding we use the generated class of the layout single_item.xml ie SingleItemBinding to add data and view in the recycler view of MainActivity.kt in our case. Comments are added before the code for better understanding.
Kotlin
import android.view.LayoutInflater import android.view.ViewGroup import androidx.recyclerview.widget.DiffUtil import androidx.recyclerview.widget.RecyclerView import com.w3wiki.rvadapterviewbinding.databinding.SingleItemBinding class RvAdapter() : RecyclerView.Adapter<RvAdapter.ViewHolder>() { private var oldLanguageList= emptyList<Language>() // create an inner class with name ViewHolder // It takes a view argument, in which pass the generated class of single_item.xml // ie SingleItemBinding and in the RecyclerView.ViewHolder(binding.root) pass it like this inner class ViewHolder(val binding: SingleItemBinding) : RecyclerView.ViewHolder(binding.root) // inside the onCreateViewHolder inflate the view of SingleItemBinding // and return new ViewHolder object containing this layout override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder { val binding = SingleItemBinding.inflate(LayoutInflater.from(parent.context), parent, false ) return ViewHolder(binding) } // bind the items with each item of the list languageList which than will be // shown in recycler view // to keep it simple we are not setting any image data to view override fun onBindViewHolder(holder: ViewHolder, position: Int) { with(holder){ with(oldLanguageList[position]){ binding.tvLangName.text = this .name binding.tvExp.text = this .exp } } } // return the size of languageList override fun getItemCount(): Int { return oldLanguageList.size } fun setData(newLanguageList : List<Language>){ val diffUtil = MyDiffUtil(oldLanguageList , newLanguageList) // it calculates the different items of the oldLanguageList and newLanguageList val diffResult = DiffUtil.calculateDiff(diffUtil) // assign oldLanguageList to newLanguageList oldLanguageList = newLanguageList diffResult.dispatchUpdatesTo( this ) } } |
Step 8: Working with the MainActivity.kt file
Go to the MainActivity.kt file and refer to the following code. Below is the code for the MainActivity.kt file. Comments are added inside the code to understand the code in more detail.
Kotlin
import androidx.appcompat.app.AppCompatActivity import android.os.Bundle import androidx.recyclerview.widget.LinearLayoutManager import com.w3wiki.rvadapterviewbinding.databinding.ActivityMainBinding class MainActivity : AppCompatActivity() { // view binding for the activity private var _binding : ActivityMainBinding? = null private val binding get() = _binding!! // get reference to the adapter class private val rvAdapter by lazy { RvAdapter() } override fun onCreate(savedInstanceState: Bundle?) { super .onCreate(savedInstanceState) _binding = ActivityMainBinding.inflate(layoutInflater) setContentView(binding.root) // define layout manager for the Recycler view binding.rvList.layoutManager = LinearLayoutManager( this ) // attach adapter to the recycler view binding.rvList.adapter = rvAdapter // create new objects val language1= Language( 1 , "Java" , "Exp : 3 years" ) val language2=Language( 2 , "Kotlin" , "Exp : 2 years" ) val language3=Language( 3 , "Python" , "Exp : 4 years" ) // call set data method of adapter class and the list data rvAdapter.setData(listOf(language1, language2, language3)) binding.btnNewLanguage.setOnClickListener { // on click of button add one more item to the list val language4= Language( 4 , "CPP" , "Exp : 5 years" ) rvAdapter.setData(listOf(language1,language2,language3,language4)) } } // on destroy of view make the binding reference to null override fun onDestroy() { super .onDestroy() _binding = null } } |
Output: