Services in Android are a special component that facilitates an application to run in the background in order to perform long-running operation tasks. The prime aim of a service is to ensure that the application remains active in the background so that the user can operate multiple applications at the same time. A user-interface is not desirable for android services as it is designed to operate long-running processes without any user intervention. A service can run continuously in the background even if the application is closed or the user switches to another application. Further, application components can bind itself to service to carry out inter-process communication(IPC). There is a major difference between android services and threads, one must not be confused between the two. Thread is a feature provided by the Operating system to allow the user to perform operations in the background. While service is an android component that performs a long-running operation about which the user might not be aware of as it does not have UI.
Types of Android Services
1. Foreground Services:
Services that notify the user about its ongoing operations are termed as Foreground Services. Users can interact with the service by the notifications provided about the ongoing task. Such as in downloading a file, the user can keep track of the progress in downloading and can also pause and resume the process.
2. Background Services:
Background services do not require any user intervention. These services do not notify the user about ongoing background tasks and users also cannot access them. The process like schedule syncing of data or storing of data fall under this service.
3. Bound Services:
This type of android service allows the components of the application like activity to bound themselves with it. Bound services perform their task as long as any application component is bound to it. More than one component is allowed to bind themselves with a service at a time. In order to bind an application component with a service bindService() method is used.
The Life Cycle of Android Services
In android, services have 2 possible paths to complete its life cycle namely Started and Bounded.
1. Started Service (Unbounded Service):
By following this path, a service will initiate when an application component calls the startService() method. Once initiated, the service can run continuously in the background even if the component is destroyed which was responsible for the start of the service. Two option are available to stop the execution of service:
- By calling stopService() method,
- The service can stop itself by using stopSelf() method.
2. Bounded Service:
It can be treated as a server in a client-server interface. By following this path, android application components can send requests to the service and can fetch results. A service is termed as bounded when an application component binds itself with a service by calling bindService() method. To stop the execution of this service, all the components must unbind themselves from the service by using unbindService() method.
To carry out a downloading task in the background, the startService() method will be called. Whereas to get information regarding the download progress and to pause or resume the process while the application is still in the background, the service must be bounded with a component which can perform these tasks.
Fundamentals of Android Services
A user-defined service can be created through a normal class which is extending the class Service. Further, to carry out the operations of service on applications, there are certain callback methods which are needed to be overridden. The following are some of the important methods of Android Services:
|
Methods |
Description |
|---|---|
| onStartCommand() |
The Android service calls this method when a component(eg: activity) requests to start a service using startService(). Once the service is started, it can be stopped explicitly using stopService() or stopSelf() methods. |
| onBind() |
This method is mandatory to implement in android service and is invoked whenever an application component calls the bindService() method in order to bind itself with a service. User-interface is also provided to communicate with the service effectively by returning an IBinder object. If the binding of service is not required then the method must return null. |
| onUnbind() |
The Android system invokes this method when all the clients get disconnected from a particular service interface. |
| onRebind() |
Once all clients are disconnected from the particular interface of service and there is a need to connect the service with new clients, the system calls this method. |
| onCreate() |
Whenever a service is created either using onStartCommand() or onBind(), the android system calls this method. This method is necessary to perform a one-time-set-up. |
| onDestroy() |
When a service is no longer in use, the system invokes this method just before the service destroys as a final clean up call. Services must implement this method in order to clean up resources like registered listeners, threads, receivers, etc. |
Example of Android Services
Playing music in the background is a very common example of services in android. From the time when a user starts the service, music play continuously in the background even if the user switches to another application. The user has to stop the service explicitly in order to pause the music. Below is the complete step-by-step implementation of this android service using a few callback methods.
Note: Following steps are performed on Android Studio version 4.0
Step 1: Create a new project
- Click on File, then New => New Project.
- Choose Empty activity
- Select language as Java/Kotlin
- Select the minimum SDK as per your need.
Step 2: Modify strings.xml file
All the strings which are used in the activity are listed in this file.
XML
<resources> <string name="app_name">Services_In_Android</string> <string name="heading">Services In Android</string> <string name="startButtonText">Start the Service</string> <string name="stopButtonText">Stop the Service</string></resources> |
Step 3: Working with the activity_main.xml file
Open the activity_main.xml file and add 2 Buttons in it which will start and stop the service. Below is the code for designing a proper activity layout.
XML
<?xml version="1.0" encoding="utf-8"?><androidx.constraintlayout.widget.ConstraintLayout android:layout_width="match_parent" android:layout_height="match_parent" android:background="#168BC34A" tools:context=".MainActivity"> <LinearLayout android:id="@+id/linearLayout" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_centerVertical="true" android:orientation="vertical" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent" app:layout_constraintVertical_bias="1.0" tools:ignore="MissingConstraints"> <TextView android:id="@+id/textView1" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginBottom="170dp" android:fontFamily="@font/roboto" android:text="@string/heading" android:textAlignment="center" android:textAppearance="@style/TextAppearance.AppCompat.Large" android:textColor="@android:color/holo_green_dark" android:textSize="36sp" android:textStyle="bold" /> <Button android:id="@+id/startButton" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_marginStart="20dp" android:layout_marginTop="10dp" android:layout_marginEnd="20dp" android:layout_marginBottom="20dp" android:background="#4CAF50" android:fontFamily="@font/roboto" android:text="@string/startButtonText" android:textAlignment="center" android:textAppearance="@style/TextAppearance.AppCompat.Display1" android:textColor="#FFFFFF" android:textStyle="bold" /> <Button android:id="@+id/stopButton" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_marginStart="20dp" android:layout_marginTop="10dp" android:layout_marginEnd="20dp" android:layout_marginBottom="20dp" android:background="#4CAF50" android:fontFamily="@font/roboto" android:text="@string/stopButtonText" android:textAlignment="center" android:textAppearance="@style/TextAppearance.AppCompat.Display1" android:textColor="#FFFFFF" android:textStyle="bold" /> <ImageView android:id="@+id/imageView" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="80dp" app:srcCompat="@drawable/banner" /> </LinearLayout> </androidx.constraintlayout.widget.ConstraintLayout> |
Step 4: Creating the custom service class
A custom service class will be created in the same directory where the MainActivity class resides and this class will extend the Service class. The callback methods are used to initiate and destroy the services. To play music, the MediaPlayer object is used. Below is the code to carry out this task.
Java
import android.app.Service;import android.content.Intent;import android.media.MediaPlayer;import android.os.IBinder;import android.provider.Settings;import androidx.annotation.Nullable; public class NewService extends Service { // declaring object of MediaPlayer private MediaPlayer player; @Override // execution of service will start // on calling this method public int onStartCommand(Intent intent, int flags, int startId) { // creating a media player which // will play the audio of Default // ringtone in android device player = MediaPlayer.create( this, Settings.System.DEFAULT_RINGTONE_URI ); // providing the boolean // value as true to play // the audio on loop player.setLooping( true ); // starting the process player.start(); // returns the status // of the program return START_STICKY; } @Override // execution of the service will // stop on calling this method public void onDestroy() { super.onDestroy(); // stopping the process player.stop(); } @Nullable @Override public IBinder onBind(Intent intent) { return null; }} |
Kotlin
import android.app.Serviceimport android.content.Intentimport android.media.MediaPlayerimport android.os.IBinderimport android.provider.Settings class NewService : Service() { // declaring object of MediaPlayer private lateinit var player:MediaPlayer // execution of service will start // on calling this method override fun onStartCommand(intent: Intent, flags: Int, startId: Int): Int { // creating a media player which // will play the audio of Default // ringtone in android device player = MediaPlayer.create(this, Settings.System.DEFAULT_RINGTONE_URI) // providing the boolean // value as true to play // the audio on loop player.setLooping(true) // starting the process player.start() // returns the status // of the program return START_STICKY } // execution of the service will // stop on calling this method override fun onDestroy() { super.onDestroy() // stopping the process player.stop() } override fun onBind(intent: Intent): IBinder? { return null }} |
Step 5: Working with the MainActivity file
Now, the button objects will be declared and the process to be performed on clicking these buttons will be defined in the MainActivity class. Below is the code to implement this step.
Java
import androidx.appcompat.app.AppCompatActivity;import android.content.Intent;import android.os.Bundle;import android.view.View;import android.widget.Button; public class MainActivity extends AppCompatActivity implements View.OnClickListener { // declaring objects of Button class private Button start, stop; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate( savedInstanceState ); setContentView( R.layout.activity_main ); // assigning ID of startButton // to the object start start = (Button) findViewById( R.id.startButton ); // assigning ID of stopButton // to the object stop stop = (Button) findViewById( R.id.stopButton ); // declaring listeners for the // buttons to make them respond // correctly according to the process start.setOnClickListener( this ); stop.setOnClickListener( this ); } public void onClick(View view) { // process to be performed // if start button is clicked if(view == start){ // starting the service startService(new Intent( this, NewService.class ) ); } // process to be performed // if stop button is clicked else if (view == stop){ // stopping the service stopService(new Intent( this, NewService.class ) ); } }} |
Kotlin
import android.content.Intentimport android.os.Bundleimport android.view.Viewimport android.widget.Buttonimport androidx.appcompat.app.AppCompatActivity class MainActivity : AppCompatActivity(), View.OnClickListener { // declaring objects of Button class private var start: Button? = null private var stop: Button? = null override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) // assigning ID of startButton // to the object start start = findViewById<View>(R.id.startButton) as Button // assigning ID of stopButton // to the object stop stop = findViewById<View>(R.id.stopButton) as Button // declaring listeners for the // buttons to make them respond // correctly according to the process start!!.setOnClickListener(this) stop!!.setOnClickListener(this) } override fun onClick(view: View) { // process to be performed // if start button is clicked if (view === start) { // starting the service startService(Intent(this, NewService::class.java)) } // process to be performed // if stop button is clicked else if (view === stop) { // stopping the service stopService(Intent(this, NewService::class.java)) } }} |
Step 6: Modify the AndroidManifest.xml file
To implement the services successfully on any android device, it is necessary to mention the created service in the AndroidManifest.xml file. It is not possible for a service to perform its task if it is not mentioned in this file. The service name is mentioned inside the application tag.
XML
<?xml version="1.0" encoding="utf-8"?> package="com.example.services_in_android"> <application android:allowBackup="true" android:icon="@mipmap/ic_launcher" android:label="@string/app_name" android:roundIcon="@mipmap/ic_launcher_round" android:supportsRtl="true" android:theme="@style/AppTheme"> <activity android:name=".MainActivity"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <meta-data android:name="preloaded_fonts" android:resource="@array/preloaded_fonts" /> <!-- Mention the service name here --> <service android:name=".NewService"/> </application> </manifest> |
