Implementation of RecyclerView in Android — What is RecyclerView in Android?
RecyclerView is a ViewGroup added to the android studio as a replacement of the GridView and ListView. The recyclerView is an enhancement on both of them (GridView & ListView) and can be found in the latest v-7 support packages. This enhancement is achieved by recycling the views which are out of the visibility of the user. For example, if a user scrolled down to a position where items 4 and 5 are visible; items 1, 2, and 3 would be cleared from the memory to reduce memory consumption.
Implementation: To implement a basic RecyclerView three sub-parts are needed to be constructed which offer the users the degree of control they require in making varying designs of their choice.
- The Card Layout: The card layout is an XML layout that will be treated as an item for the list created by the RecyclerView.
- The ViewHolder: The ViewHolder is a java class that stores the reference to the card layout views that can be modified during the execution of the program by a list of data obtained either by online databases or added in some other way.
- The Data Class: The Data class is a custom java class that acts as a structure for holding the information for every item of the RecyclerView.
Implementation of the RecyclerView:
custom_layout.xml (card layout)
<?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" android:orientation=”vertical”
android:layout_width=”match_parent” android:layout_height=”wrap_content”>
<androidx.cardview.widget.CardView
android:layout_margin=”5dp”
app:cardCornerRadius=”10dp”
app:cardElevation=”8dp”
android:layout_width=”match_parent”
android:layout_height=”wrap_content”>
<RelativeLayout
android:id=”@+id/item”
android:layout_width=”match_parent”
android:layout_height=”wrap_content”
android:padding=”10dp”>
<ImageView
android:layout_width=”100dp”
android:layout_height=”100dp”
android:id=”@+id/image”
android:layout_margin=”5dp”
android:src=”@mipmap/ic_launcher”/>
<TextView
android:id=”@+id/name”
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:layout_toRightOf=”@+id/image”
android:text=”Name”
android:textSize=”22sp”
android:textStyle=”bold”
android:textColor=”#000"
android:layout_marginLeft=”16dp”/>
<TextView
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:id=”@+id/tag”
android:text=”Tag”
android:layout_toRightOf=”@+id/image”
android:layout_below=”@+id/name”
android:layout_marginLeft=”16dp”
android:layout_marginTop=”8dp”
android:textColor=”#8D8D8D”
android:textSize=”18sp”
android:textStyle=”italic”/>
</RelativeLayout>
</androidx.cardview.widget.CardView>
</LinearLayout>
Model.java (data class)
package com.example.recyclerview;
public class Model {
//variables related to the custom layout
int image;
String name, tag;
//constructor
public Model(int image, String name, String tag) {
this.image = image;
this.name = name;
this.tag = tag;
}
//getter and setter
public int getImage() {
return image;
}
public void setImage(int image) {
this.image = image;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getTag() {
return tag;
}
public void setTag(String tag) {
this.tag = tag;
}
}
What is the Adapter?
The adapter is the main code responsible for RecyclerView. It contains all the important methods of dealing with the implementation of RecylcerView. The basic methods for a successful implementation are:
- onCreateViewHolder: which deals with the inflation of the card layout as an item for the RecyclerView.
- onBindViewHolder: which deals with the setting of different data and methods related to clicks on particular items of the RecyclerView.
- getItemCount: which Returns the length of the RecyclerView.
- onAttachedToRecyclerView: which attaches the adapter to the RecyclerView.
Below an example of a custom adapter:
CustomAdapter.java
package com.example.recyclerview;
import android.content.Context;
import android.content.Intent;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.RelativeLayout;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import java.util.List;public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.MyViewHolder> {
//create a list to pass our Model class
List<Model> modelList;
Context context;
public CustomAdapter(List<Model> modelList, Context context) {
this.modelList = modelList;
this.context = context;
}
@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
//inflate our custom view
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.custom_layout,parent,false);
return new MyViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
//bind all custom views by its position
//to get the positions we call our Model class
final Model model = modelList.get(position);
holder.name.setText(model.getName());
holder.tag.setText(model.getTag());
holder.imageView.setImageDrawable(context.getResources().getDrawable(model.getImage()));
//click listener
holder.relativeLayout.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(context,DetailsActivity.class);
intent.putExtra(“image”,model.getImage());
intent.putExtra(“name”,model.getName());
intent.putExtra(“tag”,model.getTag());
context.startActivity(intent);
}
});
}
@Override
public int getItemCount() {
return modelList.size();
}
//all the custom view will be hold here or initialize here inside MyViewHolder
class MyViewHolder extends RecyclerView.ViewHolder{
ImageView imageView;
TextView name, tag;
RelativeLayout relativeLayout;
public MyViewHolder(@NonNull View itemView) {
super(itemView);
imageView = itemView.findViewById(R.id.image);
name = itemView.findViewById(R.id.name);
tag = itemView.findViewById(R.id.tag);
relativeLayout = itemView.findViewById(R.id.item);
}
}
}
RecyclerView Implementation in an activity:
activity_main.xml
<?xml version=”1.0" encoding=”utf-8"?>
<RelativeLayout 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”
android:background=”#E9E9E9"><androidx.recyclerview.widget.RecyclerView
android:layout_width=”match_parent”
android:layout_height=”match_parent”
android:id=”@+id/recyclerView”/></RelativeLayout>
MainActivity.java
package com.example.recyclerview;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;import android.os.Bundle;
import java.util.ArrayList;
import java.util.List;public class MainActivity extends AppCompatActivity {
RecyclerView recycler;
List<Model> modelList;
RecyclerView.Adapter adapter;@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);modelList = new ArrayList<>();
recycler = findViewById(R.id.recyclerView);
recycler.setHasFixedSize(true);
recycler.setLayoutManager(new LinearLayoutManager(this));
//call our items
modelList.add(new Model(R.drawable.apple,”A”,”A for Apple”));
modelList.add(new Model(R.drawable.ball,”B”,”B for Ball”));
modelList.add(new Model(R.drawable.cat,”C”,”C for Cat”));
modelList.add(new Model(R.drawable.donkey,”D”,”D for Donkey”));
modelList.add(new Model(R.drawable.elephant,”E”,”E for Elephant”));
modelList.add(new Model(R.drawable.fish,”F”,”F for Fish”));
modelList.add(new Model(R.drawable.goat,”G”,”G for Goat”));
modelList.add(new Model(R.drawable.hat,”H”,”H for Hat”));
modelList.add(new Model(R.drawable.ink,”I”,”I for Ink”));
modelList.add(new Model(R.drawable.jug,”J”,”J for Jug”));
//init the adapter with model list and context
adapter = new CustomAdapter(modelList,getApplicationContext());
//set the adapter into recyclerView
recycler.setAdapter(adapter);
}
}
Output
