This blog defines code for DropDownList in Android.

Steps

MainActivity.java

package com.example.dropdownlist;

import android.app.Activity;

import android.os.Bundle;

import android.view.View;

import android.widget.AdapterView;

import android.widget.AdapterView.OnItemSelectedListener;

import android.widget.ArrayAdapter;

import android.widget.RelativeLayout;

import android.widget.Spinner;

import android.widget.TextView;

import android.widget.Toast;

public class MainActivity extends Activity {

Spinner spnr;

RelativeLayout rl;

String[] str={"Select","Yellow","red","Green","White"};

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

spnr=(Spinner)findViewById(R.id.sss);

rl=(RelativeLayout)findViewById(R.id.rrr);

ArrayAdapter<String> adap = new ArrayAdapter<String>(this,android.R.layout.simple_selectable_list_item,str);

spnr.setAdapter(adap);

spnr.setOnItemSelectedListener(new OnItemSelectedListener() {

@Override

public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2,

long arg3) {

// TODO Auto-generated method stub

String ss =((TextView)arg1).getText().toString();

Toast.makeText(getApplicationContext(),ss,40000).show();

}

@Override

public void onNothingSelected(AdapterView<?> arg0) {

// TODO Auto-generated method stub

}

});

}

}

Code - activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity"
android:id="@+id/rrr">
<Spinner
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/sss" />
</RelativeLayout>

Output