Tag: IPC

Android provides many ways to perform background tasks, such as Services, WorkManager, or even threads. In this tutorial, we will learn how to create a Service for our Android app.

At the end of the tutorial, you would have learned:

1. How to create a Service.

1. Android Studio. The version used in this tutorial is Bumblebee 2021.1.1 Patch 2.

1. Basic Android.

To follow along with the tutorial, perform the steps below:

1. Create a new Android project with the default Empty Activity.

2. Replace activity_main.xml with the code below. This removes the default Hello World! Textview and adds two Buttons for starting and stopping the Service.

    <?xml version="1.0" encoding="utf-8"?>
    <androidx.constraintlayout.widget.ConstraintLayout 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">
   
       <Button
           android:id="@+id/button_startService"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:text="@string/start_service"
           app:layout_constraintBottom_toBottomOf="parent"
           app:layout_constraintEnd_toStartOf="@+id/button_stopService"
           app:layout_constraintHorizontal_bias="0.5"
           app:layout_constraintStart_toStartOf="parent"
           app:layout_constraintTop_toTopOf="parent" />
   
       <Button
           android:id="@+id/button_stopService"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:text="@string/stop_service"
           app:layout_constraintBottom_toBottomOf="parent"
           app:layout_constraintEnd_toEndOf="parent"
           app:layout_constraintHorizontal_bias="0.5"
           app:layout_constraintStart_toEndOf="@+id/button_startService"
           app:layout_constraintTop_toTopOf="parent" />
    </androidx.constraintlayout.widget.ConstraintLayout>

3. Add the <string> resources below into strings.xml.

    <string name="start_service">Start Service</string>
    <string name="stop_service">Stop Service</string>

4. In MainActivity#onCreate(), obtain a reference to button_startService.

    val startServiceButton = findViewById<Button>(R.id.button_startService)

5. Obtain a reference to button_stopService as well.

    val stopServiceButton = findViewById<Button>(R.id.button_stopService)

A service is a class that extends Android.app.Service. From the Service class, the only required function that we must override is the onBind() function. There are other functions such as onStartCommand() or onDestroy() for us to override as well.

There are three different types of Service:

1. Foreground Service: A service that the user is aware of.
2. Background Service: A service that the user is not aware of.
3. Bound Service: A service where the calling client binds to it. It can communicate with the client via IPC (interprocess communication). If the service is not a bound service, then we can just return null from the onBind() function.

To create a Service class, follow the steps below.

1. Create a new class called SampleService.

    class SampleService {
   
    }

2. Adds Service as the parent class.

    class SampleService : Service() {
   
    }

3. Implements onBind() by simply returning null.

    override fun onBind(p0: Intent?): IBinder? = null

4. That is all that is needed for the Service to work, but let us add some basic functionality, such as displaying a Toast when it starts. To do that, we will override onStartCommand().

    override fun onStartCommand(intent: Intent, flags: Int, startId: Int): Int {
       Toast.makeText(
           this,
           "Service Started",
           Toast.LENGTH_SHORT
       ).show()
   
       return START_NOT_STICKY
    }

5. Also, override onDestroy() to display another Toast when the Service is stopped.

    override fun onDestroy() {
       super.onDestroy()
   
       Toast.makeText(
           this,
           "Service Stopped",
           Toast.LENGTH_SHORT
       ).show()
    }

Next, we will have to register the Service in the Manifest using <service>. In AndroidManifest.xml, inside of the <application> tag, add the <service> tag below.

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

android:exported=false is a flag that prevents other Apps from using our Service.

To start the service, we can call the startService() function from the Context object. It takes an Intent object. To enable starting and stopping the service, follow the steps below.

1. In MainActivity#onCreate, create an Intent to start our SampleService. Here, we pass in the context object and the Class object of the Service.

    val serviceIntent = Intent(
       this,
       SampleService::class.java
    )

2. Now, bind button_startService to the startService() call.

    startServiceButton.setOnClickListener{
       startService(serviceIntent)
    }

3. Lastly, bind button_stopService to the stopService() function.

    stopServiceButton.setOnClickListener {
       stopService(serviceIntent)
    }

We are now ready to run the app. Pressing the Start Service Button should start SampleService, and pressing Stop Service Button should stop SampleService. Refer to the Gif below to check your Apps behavior.

SampleService.kt

package com.codelab.daniwebandroidcreateaservice

import android.app.Service
import android.content.Intent
import android.os.IBinder
import android.widget.Toast

class SampleService : Service() {
   override fun onBind(p0: Intent?): IBinder? = null

   override fun onStartCommand(intent: Intent, flags: Int, startId: Int): Int {
       Toast.makeText(
           this,
           "Service Started",
           Toast.LENGTH_SHORT
       ).show()

       return START_NOT_STICKY
   }

   override fun onDestroy() {
       super.onDestroy()

       Toast.makeText(
           this,
           "Service Stopped",
           Toast.LENGTH_SHORT
       ).show()
   }

}

strings.xml

<resources>
   <string name="app_name">Daniweb Android Create a Service</string>
   <string name="start_service">Start Service</string>
   <string name="stop_service">Stop Service</string>
</resources>

MainActivity.kt

package com.codelab.daniwebandroidcreateaservice

import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button

class MainActivity : AppCompatActivity() {
   override fun onCreate(savedInstanceState: Bundle?) {
       super.onCreate(savedInstanceState)
       setContentView(R.layout.activity_main)

       val startServiceButton = findViewById<Button>(R.id.button_startService)
       val stopServiceButton = findViewById<Button>(R.id.button_stopService)

       val serviceIntent = Intent(
           this,
           SampleService::class.java
       )

       startServiceButton.setOnClickListener{
           startService(serviceIntent)
       }

       stopServiceButton.setOnClickListener {
           stopService(serviceIntent)
       }

   }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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">

   <Button
       android:id="@+id/button_startService"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:text="@string/start_service"
       app:layout_constraintBottom_toBottomOf="parent"
       app:layout_constraintEnd_toStartOf="@+id/button_stopService"
       app:layout_constraintHorizontal_bias="0.5"
       app:layout_constraintStart_toStartOf="parent"
       app:layout_constraintTop_toTopOf="parent" />

   <Button
       android:id="@+id/button_stopService"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:text="@string/stop_service"
       app:layout_constraintBottom_toBottomOf="parent"
       app:layout_constraintEnd_toEndOf="parent"
       app:layout_constraintHorizontal_bias="0.5"
       app:layout_constraintStart_toEndOf="@+id/button_startService"
       app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

AndroidManifest.xml

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

   <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/Theme.DaniwebAndroidCreateAService">
       <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>
       </activity>
       <service android:name=".SampleService"
           android:exported="false"/>
   </application>

</manifest>

We have learned how to create a Service in this tutorial. The full project code can be found at https://github.com/dmitrilc/DaniwebAndroidCreateService