RecycleView in Android

RecyclerView in Android makes it easy to efficiently display large sets of data. In RecycleView we supply the data and define how each item looks, and the RecyclerView library dynamically creates the elements when they’re needed

Table of Contents

Key classes in RecycleView

RecyclerView is the ViewGroup that contains the views corresponding to your data. It’s a view itself, so you add RecyclerView into your layout the way you would add any other UI element
Each individual element in the list is defined by a view holder object. When the view holder is created, it doesn’t have any data associated with it. After the view holder is created, the RecyclerView binds it to its data
The RecyclerView requests those views, and binds the views to their data, by calling methods in the adapter. You define the adapter by extending RecyclerView.Adapter
The layout manager arranges the individual elements in our list. we can use one of the layout managers provided by the RecyclerView library, or we can define our own. Layout managers are all based on the library’s LayoutManager abstract class.

Plan your layout in RecycleView

The items in your RecyclerView are arranged by a LayoutManager class. The RecyclerView library provides three layout managers, which handle the most common layout situations

LinearLayoutManager arranges the items in a one-dimensional list
GridLayoutManager arranges all items in a two-dimensional grid
- If the grid is arranged vertically, GridLayoutManager tries to make all the elements in each row have the same width and height, but different rows can have different heights.
- If the grid is arranged horizontally, GridLayoutManager tries to make all the elements in each column have the same width and height, but different columns can have different widths.

StaggeredGridLayoutManager is similar to GridLayoutManager, but it does not require that items in a row have the same height (for vertical grids) or items in the same column have the same width (for horizontal grids). The result is that the items in a row or column can end up offset from each other.

Implementing your adapter and view holder

After determined layout, we need to implement your Adapter and ViewHolder. These two classes work together to define how your data is displayed. The ViewHolder is a wrapper around a View that contains the layout for an individual item in the list. The Adapter creates ViewHolder objects as needed, and also sets the data for those views. The process of associating views to their data is called binding

we need to override three key methods:

onCreateViewHolder(): RecyclerView calls this method whenever it needs to create a new ViewHolder. The method creates and initializes the ViewHolder and its associated View, but does not fill in the view’s contents—the ViewHolder has not yet been bound to specific data

onBindViewHolder(): RecyclerView calls this method to associate a ViewHolder with data. The method fetches the appropriate data and uses the data to fill in the view holder’s layout. For example, if the RecyclerView displays a list of names, the method might find the appropriate name in the list and fill in the view holder’s TextView widget.

getItemCount(): RecyclerView calls this method to get the size of the data set. For example, in an address book app, this might be the total number of addresses. RecyclerView uses this to determine when there are no more items that can be displayed.

RecycleView project Example

MainActivity.java

package tech.softbinarycrunch.recycleview;

import android.os.Bundle;

import com.google.android.material.snackbar.Snackbar;

import androidx.appcompat.app.AppCompatActivity;

import android.view.LayoutInflater;
import android.view.View;

import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.AppBarConfiguration;
import androidx.navigation.ui.NavigationUI;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import tech.softbinarycrunch.recycleview.databinding.ActivityMainBinding;

import android.view.Menu;
import android.view.MenuItem;
import android.view.ViewGroup;
import android.widget.RelativeLayout;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private AppBarConfiguration appBarConfiguration;
    private ActivityMainBinding binding;
    String[] cars = {"Volvo", "BMW", "Ford", "Mazda", "Mazda", "Mazda", "Mazda", "Mazda", "Mazda"
            , "Mazda", "Mazda", "Mazda", "Mazda", "Mazda", "Mazda", "Mazda"
            , "Mazda"
            , "Mazda", "Mazda", "Mazda", "Mazda", "Mazda", "Mazda", "Mazda", "Mazda"
            , "Mazda", "Mazda", "Mazda", "Mazda", "Mazda", "Mazda", "Mazda", "Mazda", "Mazda"
            , "Mazda", "Mazda", "Mazda", "Mazda", "Mazda"};

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        RecyclerView rv=findViewById(R.id.animall);
       rv.setLayoutManager(new LinearLayoutManager(this));
        CustomAdapter cv=new CustomAdapter(cars);
        rv.setAdapter(cv);
    }
   }

 class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.ViewHolder> {

    private String[] localDataSet;

    /**
     * Provide a reference to the type of views that you are using
     * (custom ViewHolder).
     */
    public static class ViewHolder extends RecyclerView.ViewHolder {
        private final TextView textView;

        public ViewHolder(View view) {
            super(view);
            // Define click listener for the ViewHolder's View

            textView = (TextView) view.findViewById(R.id.textView);
        }

        public TextView getTextView() {
            return textView;
        }
    }

    /**
     * Initialize the dataset of the Adapter.
     *
     * @param dataSet String[] containing the data to populate views to be used
     * by RecyclerView.
     */
    public CustomAdapter(String[] dataSet) {
        localDataSet = dataSet;
    }

    // Create new views (invoked by the layout manager)
    @Override
    public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
        // Create a new view, which defines the UI of the list item
        View view = LayoutInflater.from(viewGroup.getContext())
                .inflate(R.layout.text_row_item, viewGroup, false);
        return new ViewHolder(view);
    }
    // Replace the contents of a view (invoked by the layout manager)
    @Override
    public void onBindViewHolder(ViewHolder viewHolder, final int position) {

        // Get element from your dataset at this position and replace the
        // contents of the view with that element
        viewHolder.getTextView().setText(localDataSet[position]);
    }
    @Override
    public int getItemCount() {
        return localDataSet.length;
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/activity">
  <androidx.recyclerview.widget.RecyclerView
      android:id="@+id/animall"
      android:layout_width="match_parent"
      android:layout_height="match_parent">
  </androidx.recyclerview.widget.RecyclerView>
</RelativeLayout>

text_row_item.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginLeft="25dp"
    android:layout_marginRight="25dp"
    android:gravity="center_vertical">
    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="wow"/>
</FrameLayout>