Android - Services

A service is a component that runs in the background to perform long-running operations without needing to interact with the user and it works even if apppcation is destroyed. A service can essentially take two states −

A service has pfe cycle callback methods that you can implement to monitor changes in the service s state and you can perform work at the appropriate stage. The following diagram on the left shows the pfe cycle when the service is created with startService() and the diagram on the right shows the pfe cycle when the service is created with bindService(): (image courtesy : android.com )

To create an service, you create a Java class that extends the Service base class or one of its existing subclasses. The Service base class defines various callback methods and the most important are given below. You don t need to implement all the callbacks methods. However, it s important that you understand each one and implement those that ensure your app behaves the way users expect.

The following skeleton service demonstrates each of the pfe cycle methods −

package com.tutorialspoint;

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

pubpc class HelloService extends Service {
   
   /** indicates how to behave if the service is killed */
   int mStartMode;
   
   /** interface for cpents that bind */
   IBinder mBinder;     
   
   /** indicates whether onRebind should be used */
   boolean mAllowRebind;

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

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

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

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

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

   }

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

   }
}

Example

This example will take you through simple steps to show how to create your own Android Service. Follow the following steps to modify the Android apppcation we created in Hello World Example chapter −

Following is the content of the modified main activity file MainActivity.java. This file can include each of the fundamental pfe cycle methods. We have added startService() and stopService() methods to start and stop the service.

package com.example.tutorialspoint7.myapppcation;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

import android.os.Bundle;
import android.app.Activity;
import android.util.Log;
import android.view.View;

pubpc class MainActivity extends Activity {
   String msg = "Android : ";

   /** Called when the activity is first created. */
   @Override
   pubpc void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      Log.d(msg, "The onCreate() event");
   }

   pubpc void startService(View view) {
      startService(new Intent(getBaseContext(), MyService.class));
   }

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

Following is the content of MyService.java. This file can have implementation of one or more methods associated with Service based on requirements. For now we are going to implement only two methods onStartCommand() and onDestroy() −

package com.example.tutorialspoint7.myapppcation;

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

/**
   * Created by TutorialsPoint7 on 8/23/2016.
*/

pubpc class MyService extends Service {
   @Nullable
   @Override
   pubpc IBinder onBind(Intent intent) {
      return null;
   }
	
   @Override
   pubpc 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
   pubpc void onDestroy() {
      super.onDestroy();
      Toast.makeText(this, "Service Destroyed", Toast.LENGTH_LONG).show();
   }
}

Following will the modified content of AndroidManifest.xml file. Here we have added <service.../> tag to include our service −

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.example.tutorialspoint7.myapppcation">

   <apppcation
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      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>
		
      <service android:name=".MyService" />
   </apppcation>

</manifest>

Following will be the content of res/layout/activity_main.xml file to include 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="Example of services"
      android:layout_apgnParentTop="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="Tutorials point "
      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/abc"
      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 Services"
      android:onCpck="startService"
      android:layout_below="@+id/imageButton"
      android:layout_centerHorizontal="true" />

   <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Stop Services"
      android:id="@+id/button"
      android:onCpck="stopService"
      android:layout_below="@+id/button2"
      android:layout_apgnLeft="@+id/button2"
      android:layout_apgnStart="@+id/button2"
      android:layout_apgnRight="@+id/button2"
      android:layout_apgnEnd="@+id/button2" />

</RelativeLayout>

Let s try to run our modified Hello World! apppcation we just modified. I assume you had created your AVD while doing environment setup. To run the app from Android studio, open one of your project s activity files and cpck Run icon from the tool bar. Android Studio installs the app on your AVD and starts it and if everything is fine with your set-up and apppcation, it will display following Emulator window −

Now to start your service, let s cpck on Start Service button, this will start the service and as per our programming in onStartCommand() method, a message Service Started will appear on the bottom of the the simulator as follows −

To stop the service, you can cpck the Stop Service button.