activity_main.xmlcountry_spinner_row.xmlCountryItem.javaCountryAdapter.javaMainActivity.java
<?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="com.codinginflow.customspinnerexample.MainActivity">

    <Spinner
        android:id="@+id/spinner_countries"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="18dp" />

</RelativeLayout>
<?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">

    <ImageView
        android:id="@+id/image_view_flag"
        android:layout_width="150dp"
        android:layout_height="100dp"
        android:src="@drawable/india" />

    <TextView
        android:id="@+id/text_view_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/image_view_flag"
        android:layout_alignParentTop="true"
        android:layout_margin="16dp"
        android:layout_toEndOf="@+id/image_view_flag"
        android:gravity="center"
        android:text="India"
        android:textColor="@android:color/black"
        android:textSize="30sp" />

</RelativeLayout>
package com.codinginflow.customspinnerexample;

public class CountryItem {
    private String mCountryName;
    private int mFlagImage;

    public CountryItem(String countryName, int flagImage) {
        mCountryName = countryName;
        mFlagImage = flagImage;
    }

    public String getCountryName() {
        return mCountryName;
    }

    public int getFlagImage() {
        return mFlagImage;
    }
}
package com.codinginflow.customspinnerexample;

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.ImageView;
import android.widget.TextView;

import java.util.ArrayList;


public class CountryAdapter extends ArrayAdapter<CountryItem> {

    public CountryAdapter(Context context, ArrayList<CountryItem> countryList) {
        super(context, 0, countryList);
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        return initView(position, convertView, parent);
    }

    @Override
    public View getDropDownView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        return initView(position, convertView, parent);
    }

    private View initView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(getContext()).inflate(
                    R.layout.country_spinner_row, parent, false
            );
        }

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

        CountryItem currentItem = getItem(position);

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

        return convertView;
    }
}
package com.codinginflow.customspinnerexample;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Spinner;
import android.widget.Toast;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {
    private ArrayList<CountryItem> mCountryList;
    private CountryAdapter mAdapter;

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

        initList();

        Spinner spinnerCountries = findViewById(R.id.spinner_countries);

        mAdapter = new CountryAdapter(this, mCountryList);
        spinnerCountries.setAdapter(mAdapter);

        spinnerCountries.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                CountryItem clickedItem = (CountryItem) parent.getItemAtPosition(position);
                String clickedCountryName = clickedItem.getCountryName();
                Toast.makeText(MainActivity.this, clickedCountryName + " selected", Toast.LENGTH_SHORT).show();
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {

            }
        });
    }

    private void initList() {
        mCountryList = new ArrayList<>();
        mCountryList.add(new CountryItem("India", R.drawable.india));
        mCountryList.add(new CountryItem("China", R.drawable.china));
        mCountryList.add(new CountryItem("USA", R.drawable.usa));
        mCountryList.add(new CountryItem("Germany", R.drawable.germany));
    }
}