Android Service

A service is a component that runs in the background to perform long-running operations that do not require user interaction. It can continue working even if the application is destroyed. Services basically have two states:

Services have lifecycle methods that can be implemented to monitor changes in the service's state and perform work at the appropriate stages. The left diagram below shows the lifecycle when a service is created via startService(), and the right diagram shows the lifecycle when a service is created via bindService():

To create a service, you need to create a Java class that extends the Service base class or one of its well-known subclasses. The Service class defines various callback methods and most important methods. You do not need to implement all the callback methods. However, it is important to understand all the methods. Implementing these callbacks ensures that your application behaves the way users expect.

The following main service demonstrates the lifecycle of each method:

package com.tutorialpro.androidservices;

import android.app.Service;
import android.os.IBinder;
import android.content.Intent;
import android.os.Bundle;

public class HelloService extends Service {

    /** Indicates the mode in which the service is to run after being killed */
    int mStartMode;

    /** Interface for clients that bind */
    IBinder mBinder;

    /** Indicates whether onRebind should be used */
    boolean mAllowRebind;

    /** Called when the service is being created. */
    @Override
    public void onCreate() {

    }

    /** Called when the service is started via startService() */
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        return mStartMode;
    }

    /** Called when clients bind to the service via bindService() */
    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }

    /** Called when all clients have unbound from the service via unbindService() */
    @Override
    public boolean onUnbind(Intent intent) {
        return mAllowRebind;
    }

    /** Called when a client binds to the service after onUnbind() has been called */
    @Override
    public void onRebind(Intent intent) {

    }

    /** Called when the service is no longer used and is being destroyed */
    @Override
    public void onDestroy() {

    }
}

Example

This example will walk you through the simple steps to create your own Android service. Follow the steps below to modify the Android application created in the Hello World example chapter:

Below is the modified content of the main activity file src/com.tutorialpro.androidservices/MainActivity.java. This file includes all basic lifecycle methods. We added startService() and stopService() methods to start and stop the service.

package com.tutorialpro.androidservices;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;

import android.content.Intent;
import android.view.View;

public class MainActivity extends Activity {

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    // Method to start the service
    public void startService(View view) {
        startService(new Intent(getBaseContext(), MyService.class));
    }

    // Method to stop the service
    public void stopService(View view) {
        stopService(new Intent(getBaseContext(), MyService.class));
    }
}

The following is the content of src/com.tutorialpro.androidservices/MyService.java. This file can implement one or more methods associated with the service based on requirements. For beginners, we only implement onStartCommand() and onDestroy():

package com.tutorialpro.androidservices;

import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.widget.Toast;

public class MyService extends Service {

    @Override
    public IBinder onBind(Intent arg0) {
        return null;
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        // Let it continue running until it is stopped.
        Toast.makeText(this, "Service Started", Toast.LENGTH_LONG).show();
        return START_STICKY;
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Toast.makeText(this, "Service Destroyed", Toast.LENGTH_LONG).show();
    }
}

The following modification is made to the AndroidManifest.xml file. Here, the <service.../> tag is added to include our service:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.tutorialpro.androidservices"
    android:versionCode="1"
    android:versionName="1.0">

    &lt;uses-sdk
        android:minSdkVersion="13"
        android:targetSdkVersion="22" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >

        &lt;activity
            android:name=".MainActivity"

<activity android:label="@string/title_activity_main">

    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>

</activity>

<service android:name=".MyService" />

</application>

</manifest>

The following is the content of the res/layout/activity_main.xml file, which includes two buttons:

<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" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Android Service Example"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:textSize="30dp" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="www.tutorialpro.org"
        android:textColor="#ff87ff09"
        android:textSize="30dp"
        android:layout_above="@+id/imageButton"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="40dp" />

    <ImageButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/imageButton"
        android:src="@drawable/ic_launcher"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/button2"
        android:text="Start Service"
        android:onClick="startService"
        android:layout_below="@+id/imageButton"
        android:layout_centerHorizontal="true" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Stop Service"
        android:id="@+id/button"
        android:onClick="stopService"
        android:layout_below="@+id/button2"
        android:layout_alignLeft="@+id/button2"
        android:layout_alignStart="@+id/button2"
        android:layout_alignRight="@+id/button2"
        android:layout_alignEnd="@+id/button2" />

</RelativeLayout>

The following is the content of the res/values/strings.xml file, which defines two new constants:

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="app_name">Android Services</string>
    <string name="title_activity_main">MainActivity</string>
    <string name="menu_settings">Settings</string>
    <string name="action_settings">Settings</string>

</resources>

Let's run the newly modified My Application app. I assume you have already created an AVD while setting up the environment. Open your activity file from your project, and click on the toolbar to run the app.

Now click the "Start Service" button to start the service, which will execute the onStartCommand() method we wrote. A message "Service has started" appears at the bottom of the emulator, as shown below:

Click the "Stop Service" button at the bottom to stop the service.