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How to listen for volume buttons in Android background service using kotlin?
This example demonstrates how to listen for volume buttons in Android background service using kotlin.
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" android:padding="24dp" tools:context=".MainActivity"> <TextView android:id="@+id/textView" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerHorizontal="true" android:text="Increase and decrease volume" android:textSize="32sp" android:textStyle="bold" /> </RelativeLayout>
Step 3 − Add the following code to src/MainActivity.kt
package app.com.kotlinapp
import android.os.Bundle
import android.os.Handler
import android.provider.Settings
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
private lateinit var settingsContentObserver: SettingsContentObserver
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
settingsContentObserver = SettingsContentObserver(this, Handler())
applicationContext.contentResolver.registerContentObserver(
Settings.System.CONTENT_URI,
true, settingsContentObserver
)
}
override fun onDestroy() {
applicationContext.contentResolver.unregisterContentObserver(settingsContentObserver)
super.onDestroy()
}
}
Step 4 − Add the following code to src/SettingsContentObserver.kt
package app.com.kotlinapp
import android.os.Bundle
import android.os.Handler
import android.provider.Settings
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
private lateinit var settingsContentObserver: SettingsContentObserver
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
settingsContentObserver = SettingsContentObserver(this, Handler())
applicationContext.contentResolver.registerContentObserver(
Settings.System.CONTENT_URI,
true, settingsContentObserver
)
}
override fun onDestroy() {
applicationContext.contentResolver.unregisterContentObserver(settingsContentObserver)
super.onDestroy()
}
}
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.myapplication"> <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"< <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 the android studio, open one of your project's activity files and click the 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.
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