How to implement an endless list with RecyclerView in Android using Kotlin?

Kotlin Apps/ApplicationsMobile DevelopmentAndroid

This example demonstrates how to implement an endless list with RecyclerView in Android using Kotlin.

Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.

Step 2 − Add the following code to res/layout/activity_main.xml.

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView 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_height="wrap_content"
   app:cardElevation="2dp"
   app:cardUseCompatPadding="true">
   <TextView
      android:id="@+id/textViewItem"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:padding="16dp"
      android:textColor="@android:color/holo_blue_bright"
      android:textStyle="bold" />
</androidx.cardview.widget.CardView>

Step 3 − Add the following code to src/MainActivity.kt

import android.os.Bundle
import android.os.Handler
import androidx.appcompat.app.AppCompatActivity
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
class MainActivity : AppCompatActivity() {
   lateinit var recyclerView: RecyclerView
   lateinit var recyclerViewAdapter: RecyclerViewAdapter
   var rowsArrayList: ArrayList<String> = ArrayList()
   var isLoading = false
   override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
      title = "KotlinApp"
      recyclerView = findViewById(R.id.recyclerView)
      populateData()
      initAdapter()
      initScrollListener()
   }
   private fun initScrollListener() {
      recyclerView.addOnScrollListener(object : RecyclerView.OnScrollListener() {
         override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
            super.onScrolled(recyclerView, dx, dy)
            val linearLayoutManager = recyclerView.layoutManager as LinearLayoutManager?
            if (!isLoading) {
               if (linearLayoutManager != null && linearLayoutManager.findLastCompletelyVisibleItemPosition() ==
               rowsArrayList.size − 1) {
                  //bottom of list!
                  loadMore()
                  isLoading = true
               }
            }
         }
      })
   }
   private fun initAdapter() {
      recyclerViewAdapter = RecyclerViewAdapter(rowsArrayList)
      recyclerView.layoutManager = LinearLayoutManager(applicationContext)
      recyclerView.adapter = recyclerViewAdapter
   }
   private fun populateData() {
      for (i in 0..9) {
         rowsArrayList.add("Number $i")
      }
   }
   private fun loadMore() {
      rowsArrayList.add(null.toString())
      recyclerViewAdapter.notifyItemInserted(rowsArrayList.size − 1)
      val handler = Handler()
      handler.postDelayed(Runnable {
         rowsArrayList.removeAt(rowsArrayList.size − 1)
         val scrollPosition = rowsArrayList.size
         recyclerViewAdapter.notifyItemRemoved(scrollPosition)
         var currentSize = scrollPosition
         val nextLimit = currentSize + 10
         while (currentSize − 1 < nextLimit) {
            rowsArrayList.add("Number $currentSize")
            currentSize++
         }
         recyclerViewAdapter.notifyDataSetChanged()
         isLoading = false
      }, 2000)
   }
}

Step 4 − Create a new class RecyclerViewAdapter.kt and add the following code −

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ProgressBar
import android.widget.TextView
import androidx.annotation.NonNull
import androidx.recyclerview.widget.RecyclerView
import androidx.recyclerview.widget.RecyclerView.ViewHolder
class RecyclerViewAdapter internal constructor(private val itemList: List<String>) :
RecyclerView.Adapter<ViewHolder>() {
   private val viewItemType = 0
   @NonNull
   override fun onCreateViewHolder(
   @NonNull parent: ViewGroup,
   viewType: Int
   ): ViewHolder {
      return if (viewType == viewItemType) {
         val view =
         LayoutInflater.from(parent.context).inflate(R.layout.item_row, parent, false)
         ItemViewHolder(view)
      } else {
         val view = LayoutInflater.from(parent.context)
         .inflate(R.layout.item_loading, parent, false)
         LoadingViewHolder(view)
      }
   }
   override fun onBindViewHolder(@NonNull viewHolder: ViewHolder, position: Int) {
      if (viewHolder is ItemViewHolder) {
         populateItemRows(viewHolder, position)
      } else if (viewHolder is LoadingViewHolder) {
         showLoadingView(viewHolder, position)
      }
   }
   override fun getItemViewType(position: Int): Int {
      return viewItemType
   }
   private inner class ItemViewHolder internal constructor(@NonNull itemView: View) :
   ViewHolder(itemView) {
      internal var tvItem: TextView = itemView.findViewById(R.id.textViewItem)
   }
   private class LoadingViewHolder internal constructor(itemView: View) :
   ViewHolder(itemView) {
      var progressBar: ProgressBar = itemView.findViewById(R.id.progressBar)
   }
   override fun getItemCount(): Int {
      return itemList.size
   }
   private fun showLoadingView(viewHolder: LoadingViewHolder, position: Int) {}
   private fun populateItemRows(viewHolder: ItemViewHolder, position: Int) {
      val item = itemList[position]
      viewHolder.tvItem.text = item
   }
}

Step 5 − Create a Layout resource file item_row.xml and add the following −

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView 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_height="wrap_content"
   app:cardElevation="2dp"
   app:cardUseCompatPadding="true">
   <TextView
      android:id="@+id/textViewItem"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:padding="16dp"
      android:textColor="@android:color/holo_blue_bright"
      android:textStyle="bold" />
</androidx.cardview.widget.CardView>

Step 6 − Create a Layout resource file item_loading.xml and add the following −

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:orientation="vertical">
   <ProgressBar
      android:id="@+id/progressBar"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_gravity="center_horizontal"
      android:indeterminate="true"
      android:paddingLeft="8dp"
      android:paddingRight="8dp" />
</LinearLayout>

Step 7 − Add the following code to androidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.q11">
   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@style/AppTheme">
      <activity android:name=".MainActivity">
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>

Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click the Run icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen

raja
Published on 09-Jul-2020 09:13:18
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