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A Service is an application component used to perform long-running tasks in background. There are 2 types of Service:

Bound Service: A bound service is the server in a client-server interface. A bound service allows components (such as activities) to bind to the service, send requests, receive responses, and even perform interprocess communication (IPC). A bound service typically lives only while it serves another application component and does not run in the background indefinitely.

Unbound Service: This service is completely independent for the Activity that called it and there is no communication or interaction between them.

We create a simple ubounded service example:

Step 1: create new project
Step 2: create new Class with name DemoService

package com.tutorialspots.service;

import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.support.annotation.Nullable;
import android.util.Log;

/**
 * Created by Tutorialspots on 1/8/2016.
 */
public class DemoService extends Service {
    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        Log.i("DemoService", "Service onBind");
        return null;
    }

    @Override
    public void onCreate() {
        Log.i("DemoService", "Service onCreate");
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.i("DemoService", "Service onStartCommand");
        return Service.START_STICKY;
    }

    @Override
    public void onDestroy() {
        Log.i("DemoService", "Service onDestroy");
    }
}

Step 3: create 2 new buttons

In file 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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.tutorialspots.service.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TUTORIALSPOTS.COM"
        android:textColor="#FF0000"
        android:textSize="30dp"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:id="@+id/textView" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Start service"
        android:id="@+id/startbtn"
        android:layout_below="@+id/textView"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="62dp" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Stop service"
        android:id="@+id/stopbtn"
        android:layout_below="@+id/startbtn"
        android:layout_centerHorizontal="true" />
</RelativeLayout>

Step 4: in file MainActivity.java

package com.tutorialspots.service;

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 startbtn, stopbtn;

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

        // get buttons
        startbtn = (Button) findViewById(R.id.startbtn);
        stopbtn = (Button) findViewById(R.id.stopbtn);

        startbtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startService(new Intent(MainActivity.this, DemoService.class));
            }
        });

        stopbtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                stopService(new Intent(MainActivity.this, DemoService.class));
            }
        });
    }
}

Explanation:
To start a service: use Context.startService() or bindService() method
To stop a service: stopSelf() or stopService().

Step 5: file AndroidManifest.xml

Declare the service:

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

    <application
        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=".DemoService"
            android:exported="false"/>
    </application>

</manifest>

Explanation:
“android:exported” means that your service is available to only your application.

Step 6: run for test

android service example

As soon as you click button Start Service, you see in the log:

01-07 18:13:32.628 2572-2572/com.tutorialspots.service I/DemoService: Service onCreate
01-07 18:13:32.628 2572-2572/com.tutorialspots.service I/DemoService: Service onStartCommand

But if you click this button again, you will see a log

01-07 18:13:32.628 2572-2572/com.tutorialspots.service I/DemoService: Service onStartCommand

Go to the manager Apps, we can see (even you close the application, you still see this)

android service example 2

android service example 3

As soon as you click button Stop service, you see in the log:

01-07 18:17:38.649 2572-2572/com.tutorialspots.service I/DemoService: Service onDestroy

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