使用kotlin语言写一个android的音乐播放器

好的，下面是一个简单的 Android 音乐播放器示例，使用 Kotlin 语言编写：

首先，需要在 AndroidManifest.xml 文件中添加以下权限：

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

然后，在 MainActivity.kt 文件中添加以下代码：

import android.media.MediaPlayer
import android.os.Bundle
import android.os.Handler
import android.os.Message
import android.util.Log
import android.view.View
import android.widget.SeekBar
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
import java.io.IOException

class MainActivity : AppCompatActivity() {

    private var mediaPlayer: MediaPlayer? = null
    private var isPlaying = false
    private var isPaused = false
    private var currentSongIndex = 0
    private var songList = mutableListOf<String>()

    private lateinit var seekBarHandler: Handler
    private lateinit var runnable: Runnable

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

        // Add songs to playlist
        songList.add("/sdcard/Music/Song1.mp3")
        songList.add("/sdcard/Music/Song2.mp3")
        songList.add("/sdcard/Music/Song3.mp3")

        // Initialize media player
        mediaPlayer = MediaPlayer()

        // Set up seek bar handler to update seek bar position
        seekBarHandler = object : Handler() {
            override fun handleMessage(msg: Message) {
                super.handleMessage(msg)
                if (mediaPlayer != null) {
                    val currentPosition = mediaPlayer!!.currentPosition
                    seek_bar.progress = currentPosition
                    val duration = mediaPlayer!!.duration
                    val progress = (currentPosition.toFloat() / duration.toFloat() * 100).toInt()
                    seek_bar_percent.text = "$progress%"
                    if (mediaPlayer!!.isPlaying) {
                        runnable = Runnable { sendMessageDelayed(obtainMessage(0), 1000) }
                        postDelayed(runnable, 1000)
                    }
                }
            }
        }

        // Set up seek bar listener to seek to specific position
        seek_bar.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener {
            override fun onProgressChanged(seekBar: SeekBar, progress: Int, fromUser: Boolean) {
                if (fromUser) {
                    mediaPlayer?.seekTo(progress)
                }
            }

            override fun onStartTrackingTouch(seekBar: SeekBar) {
                seekBarHandler.removeCallbacks(runnable)
            }

            override fun onStopTrackingTouch(seekBar: SeekBar) {
                seekBarHandler.removeCallbacks(runnable)
                mediaPlayer?.seekTo(seekBar.progress)
                runnable = Runnable { seekBarHandler.sendEmptyMessage(0) }
                seekBarHandler.postDelayed(runnable, 1000)
            }
        })

        // Set up play button listener to play or pause current song
        btn_play.setOnClickListener {
            if (!isPlaying) {
                if (isPaused) {
                    mediaPlayer?.start()
                    isPaused = false
                } else {
                    playSong(currentSongIndex)
                }
                isPlaying = true
                btn_play.setImageResource(R.drawable.ic_pause)
            } else {
                mediaPlayer?.pause()
                isPaused = true
                isPlaying = false
                btn_play.setImageResource(R.drawable.ic_play)
            }
        }

        // Set up next button listener to play next song in playlist
        btn_next.setOnClickListener {
            if (currentSongIndex < songList.size - 1) {
                currentSongIndex++
            } else {
                currentSongIndex = 0
            }
            playSong(currentSongIndex)
        }

        // Set up previous button listener to play previous song in playlist
        btn_prev.setOnClickListener {
            if (currentSongIndex > 0) {
                currentSongIndex--
            } else {
                currentSongIndex = songList.size - 1
            }
            playSong(currentSongIndex)
        }
    }

    override fun onDestroy() {
        super.onDestroy()
        mediaPlayer?.stop()
        mediaPlayer?.release()
        mediaPlayer = null
        seekBarHandler.removeCallbacks(runnable)
    }

    private fun playSong(index: Int) {
        try {
            mediaPlayer?.reset()
            mediaPlayer?.setDataSource(songList[index])
            mediaPlayer?.prepare()
            mediaPlayer?.start()
            seek_bar.max = mediaPlayer!!.duration
            seekBarHandler.sendEmptyMessage(0)
            isPlaying = true
            btn_play.setImageResource(R.drawable.ic_pause)
        } catch (e: IOException) {
            Log.e("MainActivity", "Error playing song: ${e.message}")
        }
    }
}

这个示例实现了以下功能：

- 播放/暂停当前歌曲；
- 播放下一首歌曲；
- 播放上一首歌曲；
- 显示歌曲进度，并允许拖动进度条到指定位置。

请注意，这只是一个简单的示例，实际的音乐播放器可能需要更复杂的功能。