In Android, a Service is a component that can perform long-running operations in the background, even when the user is not interacting with the application. Let’s explore the concept of Services in Android.

What is a Service?

A Service is an application component that can perform long-running operations in the background. It does not provide a user interface. Once started, a service might continue running for some time, even after the user switches to another application.

Types of Services

There are two types of services in Android:

1. Started Service: A service is started when an application component (like an activity) starts it by calling startService(). Once started, a service can run in the background indefinitely, even if the component that started it is destroyed.

2. Bound Service: A service is bound when an application component binds to it by calling bindService(). A bound service offers a client-server interface that allows components to interact with the service, send requests, receive results, and even do so across processes with interprocess communication (IPC).

Service Lifecycle

The lifecycle of a service is much simpler than that of an activity. It has only two states:

• Started State: The service enters this state when the startService() method is called. The service can run indefinitely in this state and must stop itself by calling stopSelf() or another component can stop it by calling stopService().

• Destroyed State: The system destroys the service after it finishes executing and is no longer needed.

Implementing a Service

To implement a service, you must create a subclass of Service or use one of its existing subclasses. In your implementation, you must override some callback methods that handle key aspects of the service lifecycle and provide a mechanism for components to bind to the service.

package in.infovistar.helloworld;

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

public class HelloService extends Service {
   
   /** indicates how to behave if the service is 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() {
     
   }

   /** The service is starting, due to a call to startService() */
   @Override
   public int onStartCommand(Intent intent, int flags, int startId) {
      return mStartMode;
   }

   /** A client is binding to the service with bindService() */
   @Override
   public IBinder onBind(Intent intent) {
      return mBinder;
   }

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

   /** Called when a client is binding to the service with bindService()*/
   @Override
   public void onRebind(Intent intent) {

   }

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

   }
}

Example

MainActvity.java

package in.infovistar.helloworld;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    private Context context;
    private Button btnStartService;
    private Button btnStopService;

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

        init();

        btnStartService.setOnClickListener(v -> {
            startService(new Intent(context, MyService.class));
        });

        btnStopService.setOnClickListener(v -> {
            stopService(new Intent(context, MyService.class));
        });

    }

    private void init() {
        context             = this;

        btnStartService     = findViewById(R.id.btn_start_service);
        btnStopService      = findViewById(R.id.btn_stop_service);

    }
}

activity_main.xml

<?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=".MainActivity">

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:layout_centerInParent="true">

        <Button
            android:id="@+id/btn_start_service"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Start Service" />

        <Button
            android:id="@+id/btn_stop_service"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Stop Service"/>

    </LinearLayout>

</RelativeLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">

    <application
        android:allowBackup="true"
        android:dataExtractionRules="@xml/data_extraction_rules"
        android:fullBackupContent="@xml/backup_rules"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.HelloWorld"
        tools:targetApi="31">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

            <meta-data
                android:name="android.app.lib_name"
                android:value="" />
        </activity>

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

    </application>

</manifest>

Output