Introduction

To create a application to run in the background of other current activities, one needs to create a Service. The Service can run indefinitely (unbounded) or can run at the lifespan of the calling activity(bounded).
Here you can see the android service lifecycle:

Android Services

Please note that a Service has a different lifecycle than activities therefore have different methods. But to begin a service in the application a call to startService() which envokes the service onCreate() method and onStart() beginning running the service.

context.startService() | ->onCreate() - >onStartCommand() [service running]

Calling the applications stopService() method to stop the service.

context.stopService() | ->onDestroy() [service stops]

Something that we didn't use in this example is bindService() which just calls the services onCreate() method but does not call the onStartCommand(). onBindService() is used to create persistance connection to the service.

context.onBindService() | ->onCreate() [service created]

This Services Demo is simple as it plays a audio file and by listening to click events of the buttons invokes the MyService service.

ServicesDemo.java

package com.example;
 
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
 
public class ServicesDemo extends Activity implements OnClickListener {
  private static final String TAG = "ServicesDemo";
  Button buttonStart, buttonStop;
 
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
 
    buttonStart = (Button) findViewById(R.id.buttonStart);
    buttonStop = (Button) findViewById(R.id.buttonStop);
 
    buttonStart.setOnClickListener(this);
    buttonStop.setOnClickListener(this);
  }
 
  public void onClick(View src) {
    switch (src.getId()) {
    case R.id.buttonStart:
      Log.d(TAG, "onClick: starting srvice");
      startService(new Intent(this, MyService.class));
      break;
    case R.id.buttonStop:
      Log.d(TAG, "onClick: stopping srvice");
      stopService(new Intent(this, MyService.class));
      break;
    }
  }
}

The custom MyService extends Service class and necessary to override various methods of its lifecycle ie onCreate(), onStartCommand(), or onDestroy()

MyService.java

package com.example;
 
import android.app.Service;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.IBinder;
import android.util.Log;
import android.widget.Toast;
 
public class MyService extends Service {
	private static final String TAG = "MyService";
	MediaPlayer player;
 
	@Override
	public IBinder onBind(Intent intent) {
		return null;
	}
 
	@Override
	public void onCreate() {
		Toast.makeText(this, "My Service Created", Toast.LENGTH_LONG).show();
		Log.d(TAG, "onCreate");
 
		player = MediaPlayer.create(this, R.raw.braincandy);
		player.setLooping(false); // Set looping
	}
 
	@Override
	public void onDestroy() {
		Toast.makeText(this, "My Service Stopped", Toast.LENGTH_LONG).show();
		Log.d(TAG, "onDestroy");
		player.stop();
	}
 
	@Override
	public void onStart(Intent intent, int startid) {
		Toast.makeText(this, "My Service Started", Toast.LENGTH_LONG).show();
		Log.d(TAG, "onStart");
		player.start();
	}
}

Necessary to let the AndroidManifest file know about your service <service android:enabled="true" android:name=".MyService" />

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
  package="com.example" android:versionCode="1" android:versionName="1.0">
  <application android:icon="@drawable/icon" android:label="@string/app_name">
    <activity android:name=".ServicesDemo" android:label="@string/app_name">
      <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
      </intent-filter>
    </activity>
    <service android:enabled="true" android:name=".MyService" />
  </application>
  <uses-sdk android:minSdkVersion="3" />
</manifest>

main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:gravity="center">
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="Services Demo" 
    android:gravity="center" android:textSize="20sp" 
    android:padding="20dp"/>
<Button android:layout_width="wrap_content" 
        android:layout_height="wrap_content" 
        android:id="@+id/buttonStart" android:text="Start">
</Button>
<Button android:layout_width="wrap_content" 
        android:layout_height="wrap_content" 
        android:text="Stop" android:id="@+id/buttonStop">
</Button>
</LinearLayout>