How Can We Prevent A Service From Being Killed By Os

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 application is destroyed. A service can essentially take two states −

Sr.No.	State & Description
1	Started A service is started when an application component, such as an activity, starts information technology by calling startService(). Once started, a service can run in the groundwork indefinitely, even if the component that started information technology is destroyed.
2	Jump A service is bound when an application component binds to it past calling bindService(). A bound service offers a client-server interface that allows components to interact with the service, send requests, get results, and even do so across processes with interprocess communication (IPC).

Sr.No.

State & Description

Started

A service is started when an application component, such as an activity, starts information technology by calling startService(). Once started, a service can run in the groundwork indefinitely, even if the component that started information technology is destroyed.

Jump

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

A service has life wheel callback methods that yous tin implement to monitor changes in the service's state and you can perform work at the appropriate stage. The post-obit diagram on the left shows the life cycle when the service is created with startService() and the diagram on the right shows the life cycle when the service is created with bindService(): (paradigm courtesy : android.com )

Android Service lifecycle

To create an service, you create a Coffee course that extends the Service base course or one of its existing subclasses. The Service base of operations class defines diverse callback methods and the most of import are given below. You lot don't need to implement all the callbacks methods. However, it's of import that you sympathise each i and implement those that ensure your app behaves the way users expect.

Sr.No.	Callback & Clarification
1	onStartCommand() The arrangement calls this method when another component, such as an activity, requests that the service be started, by calling startService(). If y'all implement this method, it is your responsibleness to stop the service when its work is done, past calling stopSelf() or stopService() methods.
2	onBind() The system calls this method when some other component wants to bind with the service past calling bindService(). If you implement this method, you must provide an interface that clients employ to communicate with the service, by returning an IBinder object. Yous must always implement this method, but if you don't want to allow binding, then you should return null.
3	onUnbind() The system calls this method when all clients have disconnected from a particular interface published by the service.
4	onRebind() The organisation calls this method when new clients have continued to the service, after it had previously been notified that all had asunder in its onUnbind(Intent).
five	onCreate() The system calls this method when the service is get-go created using onStartCommand() or onBind(). This call is required to perform i-fourth dimension set-upward.
half dozen	onDestroy() The system calls this method when the service is no longer used and is beingness destroyed. Your service should implement this to make clean upward any resources such equally threads, registered listeners, receivers, etc.

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

package com.tutorialspoint;  import android.app.Service; import android.os.IBinder; import android.content.Intent; import android.os.Bundle;  public form HelloService extends Service {        /** indicates how to conduct 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 phone call to startService() */    @Override    public int onStartCommand(Intent intent, int flags, int startId) {       render 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

This example will accept you through simple steps to show how to create your ain Android Service. Follow the following steps to modify the Android application we created in Hello World Instance chapter −

Step	Description
1	You volition employ Android StudioIDE to create an Android awarding and name information technology equally My Application nether a package com.example.tutorialspoint7.myapplication as explained in the Howdy World Example affiliate.
2	Alter main activity file MainActivity.java to add together startService() and stopService() methods.
three	Create a new coffee file MyService.java nether the package com.example.My Application. This file will take implementation of Android service related methods.
4	Define your service in AndroidManifest.xml file using <service.../> tag. An awarding can have one or more than services without whatever restrictions.
v	Change the default content of res/layout/activity_main.xml file to include 2 buttons in linear layout.
6	No need to modify whatsoever constants in res/values/strings.xml file. Android studio take intendance of string values
7	Run the awarding to launch Android emulator and verify the result of the changes done in the application.

Following is the content of the modified master activity file MainActivity.coffee. This file tin include each of the fundamental life cycle methods. We have added startService() and stopService() methods to showtime and end the service.

bundle com.example.tutorialspoint7.myapplication;  import android.content.Intent; import android.support.v7.app.AppCompatActivity; import android.os.Bundle;  import android.bone.Package; import android.app.Activity; import android.util.Log; import android.view.View;  public class MainActivity extends Activity {    Cord msg = "Android : ";     /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {       super.onCreate(savedInstanceState);       setContentView(R.layout.activity_main);       Log.d(msg, "The onCreate() event");    }     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));    } }

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

package com.example.tutorialspoint7.myapplication;  import android.app.Service; import android.content.Intent; import android.bone.IBinder; import android.support.annotation.Nullable; import android.widget.Toast;  /**    * Created by TutorialsPoint7 on 8/23/2016. */  public grade MyService extends Service {    @Nullable    @Override    public IBinder onBind(Intent intent) {       return null;    } 	    @Override    public int onStartCommand(Intent intent, int flags, int startId) {       // Let information technology continue running until information technology 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();    } }

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

<?xml version="1.0" encoding="utf-viii"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="com.example.tutorialspoint7.myapplication">     <application       android:allowBackup="true"       android:icon="@mipmap/ic_launcher"       android:label="@string/app_name"       android:supportsRtl="true"       android:theme="@fashion/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:proper name=".MyService" />    </application>  </manifest>

Post-obit volition 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="Case of services"       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="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="truthful"       android:layout_centerHorizontal="true" />     <Button       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:id="@+id/button2"       android:text="Get-go Services"       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="End Services"       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>

Let's try to run our modified Hello Earth! awarding we merely 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 click Run Android StudioRun Icon icon from the tool bar. Android Studio installs the app on your AVD and starts information technology and if everything is fine with your set up-upward and application, information technology will brandish following Emulator window −

Android Service Demo

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

Android Service Start