How to run an Android service always in background?

This example demonstrates how do I run an android service always in background.
Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.
Step 2 − Add the following code to res/layout/activity_main.xml.
<?xml version="1.0" encoding="utf-8"?>
<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">
   <Button
      android:id="@+id/button"
      android:text="Click here to start background Service"
      android:textStyle="bold"
      android:textSize="16sp"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerInParent="true" />
</RelativeLayout>
Step 3 – Right click on the project, Select New >> Service >> Service and add the following to MyServices.java
package app.com.sample;
import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.widget.Toast;
public class MyService extends Service {
   public MyService() {
   }
   @Override
   public int onStartCommand(Intent intent, int flags, int startId){
      onTaskRemoved(intent);
      Toast.makeText(getApplicationContext(),"This is a Service running in Background",
      Toast.LENGTH_SHORT).show();
      return START_STICKY;
   }
   @Override
   public IBinder onBind(Intent intent) {
      // TODO: Return the communication channel to the service.
      throw new UnsupportedOperationException("Not yet implemented");
   }
   @Override
   public void onTaskRemoved(Intent rootIntent) {
      Intent restartServiceIntent = new Intent(getApplicationContext(),this.getClass());
      restartServiceIntent.setPackage(getPackageName());
      startService(restartServiceIntent);
      super.onTaskRemoved(rootIntent);
   }
}
Step 4 − Add the following code to src/MainActivity.java
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
   Button button;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      button = findViewById(R.id.button);
      button.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            startService(new Intent(getApplicationContext(),MyService.class));
         }
      });
   }
}
Step 5 - Add the following code to androidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="app.com.sample">
   <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">
      <service
         android:name=".MyService"
         android:enabled="true"
         android:exported="true"></service>
      <activity android:name=".MainActivity">
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>
Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click Run  icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen –
 
Click here to download the project code.