AutoCompleteCountryAdapter.javaactivity_main.xmlcountry_autocomplete_row.xmlCountryItem.javaMainActivity.java
package com.codinginflow.customautocompleteexample;

import android.content.Context;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Filter;
import android.widget.ImageView;
import android.widget.TextView;

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


public class AutoCompleteCountryAdapter extends ArrayAdapter<CountryItem> {
    private List<CountryItem> countryListFull;

    public AutoCompleteCountryAdapter(@NonNull Context context, @NonNull List<CountryItem> countryList) {
        super(context, 0, countryList);
        countryListFull = new ArrayList<>(countryList);
    }

    @NonNull
    @Override
    public Filter getFilter() {
        return countryFilter;
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(getContext()).inflate(
                    R.layout.country_autocomplete_row, parent, false
            );
        }

        TextView textViewName = convertView.findViewById(R.id.text_view_name);
        ImageView imageViewFlag = convertView.findViewById(R.id.image_view_flag);

        CountryItem countryItem = getItem(position);

        if (countryItem != null) {
            textViewName.setText(countryItem.getCountryName());
            imageViewFlag.setImageResource(countryItem.getFlagImage());
        }

        return convertView;
    }

    private Filter countryFilter = new Filter() {
        @Override
        protected FilterResults performFiltering(CharSequence constraint) {
            FilterResults results = new FilterResults();
            List<CountryItem> suggestions = new ArrayList<>();

            if (constraint == null || constraint.length() == 0) {
                suggestions.addAll(countryListFull);
            } else {
                String filterPattern = constraint.toString().toLowerCase().trim();

                for (CountryItem item : countryListFull) {
                    if (item.getCountryName().toLowerCase().contains(filterPattern)) {
                        suggestions.add(item);
                    }
                }
            }

            results.values = suggestions;
            results.count = suggestions.size();

            return results;
        }

        @Override
        protected void publishResults(CharSequence constraint, FilterResults results) {
            clear();
            addAll((List) results.values);
            notifyDataSetChanged();
        }

        @Override
        public CharSequence convertResultToString(Object resultValue) {
            return ((CountryItem) resultValue).getCountryName();
        }
    };
}
<?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"
    android:padding="16dp"
    tools:context="com.codinginflow.customautocompleteexample.MainActivity">

    <AutoCompleteTextView
        android:id="@+id/actv"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:completionThreshold="1"
        android:hint="Select a country" />

</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="4dp">

    <ImageView
        android:id="@+id/image_view_flag"
        android:layout_width="60dp"
        android:layout_height="40dp"
        tools:src="@drawable/flag_afghanistan" />

    <TextView
        android:id="@+id/text_view_name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:paddingStart="8dp"
        android:textAppearance="?android:attr/textAppearanceListItemSmall"
        tools:text="Afghanistan" />

</LinearLayout>
package com.codinginflow.customautocompleteexample;

public class CountryItem {
    private String countryName;
    private int flagImage;

    public CountryItem(String countryName, int flagImage) {
        this.countryName = countryName;
        this.flagImage = flagImage;
    }

    public String getCountryName() {
        return countryName;
    }

    public int getFlagImage() {
        return flagImage;
    }
}
package com.codinginflow.customautocompleteexample;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.AutoCompleteTextView;

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

public class MainActivity extends AppCompatActivity {
    private List<CountryItem> countryList;

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

        fillCountryList();

        AutoCompleteTextView editText = findViewById(R.id.actv);
        AutoCompleteCountryAdapter adapter = new AutoCompleteCountryAdapter(this, countryList);
        editText.setAdapter(adapter);
    }

    private void fillCountryList() {
        countryList = new ArrayList<>();
        countryList.add(new CountryItem("Afghanistan", R.drawable.flag_afghanistan));
        countryList.add(new CountryItem("Albania", R.drawable.flag_albania));
        countryList.add(new CountryItem("Algeria", R.drawable.flag_algeria));
        countryList.add(new CountryItem("Andorra", R.drawable.flag_andorra));
        countryList.add(new CountryItem("Angola", R.drawable.flag_angola));
    }
}