Music Player App in Android using Kotlin

This guide will walk you through creating a music player app using Android and Kotlin. The app will allow users to play music files from the external/internal storage of their phones and include features such as play/pause, forward/backward, loop/repeat, a draggable progress bar, and additional custom features.

Table of Contents

1. Project Setup
   • Create a New Android Project
   • Add Necessary Dependencies
2. Understanding the Key APIs and Libraries
   • MediaPlayer
   • MediaStore
   • SeekBar
   • Handler
   • SharedPreferences
3. Designing the UI
   • Layout Design (XML)
   • Adding Buttons and SeekBar
4. Implementing Core Features
   • Accessing Music Files
   • Initializing MediaPlayer
   • Implementing Play/Pause Functionality
   • Forward/Backward Functionality
   • Loop/Repeat Functionality
   • Draggable Progress Bar
5. Extra Custom Features
   • Handling Audio Focus
   • Saving User Preferences
   • Customizing UI Elements
6. Final Touches
   • Testing
   • Debugging
   • Packaging and Deployment

1. Project Setup

Create a New Android Project

1. Open Android Studio.
2. Click on "Create New Project."
3. Choose "Empty Activity" and click "Next."
4. Name your project (e.g., MusicPlayerApp).
5. Select Kotlin as the programming language.
6. Finish the setup.

Add Necessary Dependencies

You might need to add some dependencies for enhanced features or UI components. Open build.gradle (Module: app) and add the following dependencies:

dependencies {
    implementation ("androidx.core:core-ktx:1.7.0")
    implementation ("androidx.appcompat:appcompat:1.4.0")
    implementation ("com.google.android.material:material:1.4.0")
    // Additional dependencies for custom features if needed
}

Sync the project to apply the changes.

2. Understanding the Key APIs and Libraries

MediaPlayer

• The MediaPlayer class is the core of this project. It handles audio playback from various sources like external/internal storage.
• You can control playback (start, stop, pause) and listen to different events using listeners.

MediaStore

• MediaStore is used to retrieve and organize multimedia content. It provides a standardized way to access audio files stored on the device.

SeekBar

• SeekBar is the UI component that allows users to track the progress of a song and jump to different positions.

Handler

• Handler is used to manage the update of the SeekBar as the song progresses. It runs tasks on the main thread at regular intervals.

SharedPreferences

• SharedPreferences allows saving user preferences, such as the last played song, loop settings, etc.

3. Designing the UI

Layout Design (XML)

Create a layout file activity_player.xml in res/layout with the following XML code:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp">

    <TextView
        android:id="@+id/song_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Song Title"
        android:textSize="20sp"
        android:textColor="@android:color/black"/>

    <SeekBar
        android:id="@+id/seekBar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/song_title"
        android:layout_marginTop="16dp"/>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/seekBar"
        android:layout_marginTop="16dp"
        android:orientation="horizontal"
        android:gravity="center">

        <ImageButton
            android:id="@+id/btn_previous"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/ic_previous"
            android:contentDescription="@string/previous_song"/>

        <ImageButton
            android:id="@+id/btn_play_pause"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/ic_play"
            android:contentDescription="@string/play_pause"/>

        <ImageButton
            android:id="@+id/btn_next"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/ic_next"
            android:contentDescription="@string/next_song"/>

        <ImageButton
            android:id="@+id/btn_repeat"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/ic_repeat"
            android:contentDescription="@string/repeat_song"/>
    </LinearLayout>
</RelativeLayout>

Adding Buttons and SeekBar

In your PlayerActivity.kt, initialize and handle the UI components, such as buttons and SeekBar.

4. Implementing Core Features

Accessing Music Files

To access audio files, you need to request the appropriate permission and use MediaStore to query available music files.

1. Request Permission: Update AndroidManifest.xml to include the permission.

   <uses-permission android:name="android.permission.READ_MEDIA_AUDIO"/>

2. Request Permission at Runtime: For Android 6.0 (API level 23) and above, request the permission at runtime in your Activity.

   private fun requestPermissions() {
       if (checkSelfPermission(android.Manifest.permission.READ_MEDIA_AUDIO) != PackageManager.PERMISSION_GRANTED) {
           requestPermissions(arrayOf(android.Manifest.permission.READ_MEDIA_AUDIO), REQUEST_PERMISSION_CODE)
       }
   }
   
   override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<out String>, grantResults: IntArray) {
       super.onRequestPermissionsResult(requestCode, permissions, grantResults)
       if (requestCode == REQUEST_PERMISSION_CODE) {
           if (grantResults.isNotEmpty() && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
               // Permission granted, proceed with accessing music files
           } else {
               // Permission denied, handle accordingly
           }
       }
   }

   Replace REQUEST_PERMISSION_CODE with a unique integer code.

3. Query Music Files: Use MediaStore to get a list of audio files.

   private fun getMusicFiles(): List<String> {
       val musicList = mutableListOf<String>()
       val projection = arrayOf(MediaStore.Audio.Media.DATA) // Path to the audio file
       val cursor = contentResolver.query(
           MediaStore.Audio.Media.EXTERNAL_CONTENT_URI,
           projection,
           null,
           null,
           null
       )
       cursor?.use {
           val dataIndex = cursor.getColumnIndexOrThrow(MediaStore.Audio.Media.DATA)
           while (cursor.moveToNext()) {
               musicList.add(cursor.getString(dataIndex))
           }
       }
       return musicList
   }

Initializing MediaPlayer

1. Create and Configure MediaPlayer: Initialize MediaPlayer and set the data source.

   private fun initializeMediaPlayer(songPath: String) {
       mediaPlayer.apply {
           reset()
           try {
               setDataSource(songPath)
               prepare()
               start()
           } catch (e: Exception) {
               e.printStackTrace()
               Log.e("PlayerActivity", "Error initializing MediaPlayer: ${e.message}")
           }
       }
   }

Implementing Play/Pause Functionality

1. Toggle Play/Pause: Change the playback state when the button is clicked.

   private fun togglePlayPause() {
       if (mediaPlayer.isPlaying) {
           mediaPlayer.pause()
           playPauseButton.setImageResource(R.drawable.ic_play) // Change to play icon
       } else {
           mediaPlayer.start()
           playPauseButton.setImageResource(R.drawable.ic_pause) // Change to pause icon
       }
   }

Forward/Backward Functionality

1. Move Forward/Backward: Update the current position of the MediaPlayer.

   private fun moveForward() {
       val currentPosition = mediaPlayer.currentPosition
       val newPosition = (currentPosition + 15000).coerceAtMost(mediaPlayer.duration)
       mediaPlayer.seekTo(newPosition)
   }
   
   private fun moveBackward() {
       val currentPosition = mediaPlayer.currentPosition
       val newPosition = (currentPosition - 15000).coerceAtLeast(0)
       mediaPlayer.seekTo(newPosition)
   }

   Adjust the 15000 milliseconds value to move forward or backward by different amounts.

Loop/Repeat Functionality

1. Toggle Repeat: Change the repeat state and update the button icon.

   private fun toggleRepeat() {
       isRepeating = !isRepeating
       repeatButton.setImageResource(
           if (isRepeating) R.drawable.ic_repeat_on else R.drawable.ic_repeat_off
       )
   }
   
   private fun setupCompletionListener() {
       mediaPlayer.setOnCompletionListener {
           if (isRepeating) {
               mediaPlayer.start() // Replay the same song
           } else {
               playNextSong() // Play the next song
           }
       }
   }

Draggable Progress Bar

1. Update and Handle SeekBar: Synchronize the SeekBar with the song's progress.

   private fun setupSeekBar() {
       seekBar.max = mediaPlayer.duration
       seekBar.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener {
           override fun onProgressChanged(seekBar: SeekBar?, progress: Int, fromUser: Boolean) {
               if (fromUser) {
                   mediaPlayer.seekTo(progress)
               }
           }
   
           override fun onStartTrackingTouch(seekBar: SeekBar?) {}
   
           override fun onStopTrackingTouch(seekBar: SeekBar?) {}
       })
   
       Timer().scheduleAtFixedRate(object : TimerTask() {
           override fun run() {
               runOnUiThread {
                   seekBar.progress = mediaPlayer.currentPosition
               }
           }
       }, 0, 1000)
   }

This setup ensures that the SeekBar reflects the current position of the song and updates as the song plays.

5. Extra Custom Features

Handling Audio Focus

Manage audio focus to ensure smooth playback when the app is in the foreground.

Saving User Preferences

Use SharedPreferences to save settings like the last played song or repeat status.

Customizing UI Elements

Enhance the user interface with custom icons and styles for a better user experience.

This documentation provides a comprehensive guide to building a music player app using Kotlin in Android. Adjust and extend the features based on your specific requirements and user feedback.