How ListView's recycling mechanism works on Android?

AndroidApps/ApplicationsMobile Development

This example demonstrates how ListView's recycling mechanism works on Android.

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"?>
<LinearLayout 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:layout_height="match_parent"
   tools:context=".MainActivity">
   <androidx.recyclerview.widget.RecyclerView
      android:id="@+id/card_recycler_view"
      android:scrollbars="vertical"
      android:layout_width="match_parent"
      android:layout_height="match_parent"/>
</LinearLayout>

Step 3 − Add the following code to res/layout/card_row.xml.

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView
   xmlns:android="http://schemas.android.com/apk/res/android"
   android:orientation="vertical"
   android:layout_width="match_parent"
   android:layout_height="wrap_content"
   android:id="@+id/card"
   android:layout_marginTop="5dp"
   android:layout_marginLeft="5dp"
   android:layout_marginRight="5dp">
   <TextView
      android:id="@+id/tv_country"
      android:layout_marginTop="10dp"
      android:layout_marginBottom="10dp"
      android:layout_gravity="center"
      android:textSize="18sp"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:textStyle="bold" />
</androidx.cardview.widget.CardView>

Step 4 − Add the following code to src/MainActivity.java

package com.app.sample;
import android.os.Bundle;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
   private ArrayList cities;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      initViews();
   }
   private void initViews(){
      RecyclerView recyclerView = (RecyclerView)findViewById(R.id.card_recycler_view);
      recyclerView.setHasFixedSize(true);
      RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getApplicationContext());
      recyclerView.setLayoutManager(layoutManager);
      cities = new ArrayList<>();
      cities.add("Mumbai");
      cities.add("Chennai");
      cities.add("Kochin");
      cities.add("Bangalore");
      cities.add("Hyderabad");
      cities.add("Amaravati");
      cities.add("Goa");
      cities.add("Trivandram");
      cities.add("Coimbatore");
      cities.add("Vellore");
      cities.add("Salem");
      cities.add("Bhubaneswar");
      cities.add("");
      cities.add("Cuttack");
      cities.add("Mysore");
      RecyclerView.Adapter adapter = new DataAdapter(cities);
      recyclerView.setAdapter(adapter);
      recyclerView.addOnItemTouchListener(new RecyclerView.OnItemTouchListener() {
         GestureDetector gestureDetector = new GestureDetector(getApplicationContext(), new GestureDetector.SimpleOnGestureListener(){
            @Override public boolean onSingleTapUp(MotionEvent e) {
               return true;
            }
         });
         @Override
         public boolean onInterceptTouchEvent(RecyclerView rv, MotionEvent e) {
            View child = rv.findChildViewUnder(e.getX(), e.getY());
            if(child != null && gestureDetector.onTouchEvent(e)) {
               int position = rv.getChildAdapterPosition(child);
               Toast.makeText(getApplicationContext(), (Integer) cities.get(position), Toast.LENGTH_SHORT).show();
            }
            return false;
         }
         @Override
         public void onTouchEvent(RecyclerView rv, MotionEvent e) {
         }
         @Override
         public void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept) {
         }
      });
   }
}

Step 5 − Add the following code to src/DataAdapter.java

package com.app.sample;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.recyclerview.widget.RecyclerView;
import java.util.ArrayList;
public class DataAdapter extends RecyclerView.Adapter<DataAdapter.ViewHolder>{
      private ArrayList<String> cities;
      public DataAdapter(ArrayList<String> countries) {
         this.cities = countries;
      }
      @Override
      public DataAdapter.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
         View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.card_row, viewGroup, false);
         return new ViewHolder(view);
      }
      @Override
      public void onBindViewHolder(DataAdapter.ViewHolder viewHolder, int i) {
         viewHolder.tv_country.setText(cities.get(i));
      }
      @Override
      public int getItemCount() {
         return cities.size();
      }
      public class ViewHolder extends RecyclerView.ViewHolder{
      private TextView tv_country;
      public ViewHolder(View view) {
         super(view);
         tv_country = (TextView)view.findViewById(R.id.tv_country);
      }
   }
}

Step 6 − Add the following code to Manifests/AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.app.sample">
   <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 the android studio, open one of your project's activity files and click Run  icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen −

Click here to download the project code.

raja
Published on 15-Nov-2019 10:26:33
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