How to sort a list in ascending order and Add header by the first letter in the RecyclerView in Android

Hello Forks ! Hope you are doing well. In this tutorial we will understand how to sort a list of data, it could be any data like bank names , places names etc. in ascending order with a header which grouped the same type of data under it. For example we have a list of banks data and we want to group all banks starting with 'A' character in single unit and so on. So without taking too much time  let's move to the coding part and understand how we can achieve this.

Step 1: Create a Model class Named Bank.java

public class Bank {
    private String name;

    public Bank(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

Step 2: Sort the List of Banks with this Method

import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public void sortBankList(List<Bank> bankList) {
    Collections.sort(bankList, new Comparator<Bank>() {
        @Override
        public int compare(Bank bank1, Bank bank2) {
            return bank1.getName().compareTo(bank2.getName());
        }
    });
}

Step 3: XML Layouts: activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#EEEEF0"
    android:orientation="vertical">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

and Create item_bank.xml under layout section

<?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"
    android:orientation="vertical"
   >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <TextView
            android:id="@+id/section_header"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:paddingLeft="20dp"
            android:background="#EEEEF0"
            android:paddingTop="5dp"
            android:paddingBottom="5dp"
            android:text=""
            android:textStyle="bold"
            android:visibility="gone"/>

        <TextView
            android:id="@+id/bank_name"
            android:layout_width="match_parent"
            android:text=""
            android:paddingBottom="3dp"
            android:paddingTop="3dp"
            android:textSize="16sp"
            android:paddingLeft="20dp"
            android:background="#FFF"
            android:layout_height="wrap_content"/>
    </LinearLayout>

</LinearLayout>

Step 4: Create RecyclerView Adapter: You need an adapter to manage the data for RecyclerView. This adapter will handle the grouping and display of bank names.

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import java.util.List;

public class BankAdapter extends RecyclerView.Adapter<BankAdapter.ViewHolder> {

    private List<Bank> bankList;

    public BankAdapter(List<Bank> bankList) {
        this.bankList = bankList;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.item_bank, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Bank bank = bankList.get(position);
        holder.bankNameTextView.setText(bank.getName());
        // Set the first letter as a section header if it’s the first occurrence
        if (position == 0 || bank.getName().charAt(0) != bankList.get(position - 1).getName().charAt(0)) {
            holder.sectionHeaderTextView.setText(String.valueOf(bank.getName().charAt(0)));
            holder.sectionHeaderTextView.setVisibility(View.VISIBLE);
        } else {
            holder.sectionHeaderTextView.setVisibility(View.GONE);
        }
    }

    @Override
    public int getItemCount() {
        return bankList.size();
    }

    public static class ViewHolder extends RecyclerView.ViewHolder {
        public TextView bankNameTextView;
        public TextView sectionHeaderTextView;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            bankNameTextView = itemView.findViewById(R.id.bank_name);
            sectionHeaderTextView = itemView.findViewById(R.id.section_header);
        }
    }
}

the magical parts in this code is happening from this line 

if (position == 0 || bank.getName().charAt(0) != bankList.get(position - 1).getName().charAt(0)) {
            holder.sectionHeaderTextView.setText(String.valueOf(bank.getName().charAt(0)));
            holder.sectionHeaderTextView.setVisibility(View.VISIBLE);
        } else {
            holder.sectionHeaderTextView.setVisibility(View.GONE);
        }

It does nothing but check if position is 0 or compare first character of each position with another.if match then group into one else set its visibility to GONE if does match.

Step 5 : Setup RecyclerView in Activity:

import android.os.Bundle;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private RecyclerView recyclerView;
    private BankAdapter bankAdapter;
    private List<Bank> bankList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        recyclerView = findViewById(R.id.recycler_view);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));

        bankList = new ArrayList<>();
        // Add sample data
        bankList.add(new Bank("Axis Bank"));
        bankList.add(new Bank("Andhra Bank"));
        bankList.add(new Bank("Allahabad Bank"));
        bankList.add(new Bank("HDFC Bank"));
        bankList.add(new Bank("ICICI Bank"));
        bankList.add(new Bank("Indian Bank"));
        bankList.add(new Bank("State Bank of India"));
        bankList.add(new Bank("Bank of Baroda"));
        bankList.add(new Bank("Bank of Maharastra"));


        sortBankList(bankList);
        bankAdapter = new BankAdapter(bankList);
        recyclerView.setAdapter(bankAdapter);
    }
}

That it . Now compile and run your program and get the output.

This setup will sort the list of banks in ascending order and group them by the first letter in the RecyclerView. Thank You....Happy coding! 😊