Android Media Player Problem

//package


import android.media.MediaPlayer
import android.os.Bundle
import android.os.Handler
import android.support.v4.app.Fragment
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Button
import android.widget.ImageView
import android.widget.SeekBar
import android.widget.TextView
import com.example.vitali.musicplayer.R
import java.text.SimpleDateFormat
import java.util.*
import kotlin.properties.Delegates



class MusicPlayerFragment: Fragment(),
    View.OnClickListener,
    MediaPlayer.OnPreparedListener,
    SeekBar.OnSeekBarChangeListener {

    companion object {

        const val TAG = "MusicPlayerFragment"

        const val STATE_CURRENT_PLAYING_POSITION = "playerPosition"
        const val STATE_IS_PLAYING = "isPlaying"

        const val UPDATE_TIME = 1000.toLong()
        val TIME_FORMATTER = SimpleDateFormat("mm:ss")
    }

    private enum class PlayerSate {
        PLAYING,
        STOPPED
    }



    //region Views
    lateinit var mainView: View

    lateinit var songName: TextView
    lateinit var songCover: ImageView
    lateinit var songCurrentTime: TextView
    lateinit var songEndTime: TextView
    lateinit var songProgressHandler: SeekBar
    lateinit var songPlayPauseButton: Button
    lateinit var songPreviousButton: Button
    lateinit var songNextButton: Button
    //endregion

    //region Properties

    private var mediaPlayer: MediaPlayer? = null
    private var mediaPlayerState: PlayerSate by Delegates.observable(PlayerSate.STOPPED) { _, _, _ ->
        updateState()
    }

    private val handler = Handler()
    private val updateProgressTask: Runnable = object : Runnable {
        override fun run() {
            try {
                updateProgress()
            } finally {
                handler.postDelayed(this, UPDATE_TIME)
            }
        }
    }

    //endregion


    //region Lifecycle methods

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        Log.d(TAG, "onCreateView")
        mainView = inflater.inflate(R.layout.fragment_music_player, container, false)
        return mainView
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        Log.d(TAG, "onViewCreated")
        super.onViewCreated(view, savedInstanceState)
        findViews(mainView)
        setupPlayPause()
        setupSeekBar()

    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        Log.d(TAG, "onActivityCreated")
        super.onActivityCreated(savedInstanceState)

        mediaPlayer = MediaPlayer.create(activity, R.raw.lobo_loco_03_streetlife_silentfilm)
        mediaPlayer!!.setOnPreparedListener(this)
        if (savedInstanceState != null){
            restoreState(savedInstanceState)
        }
    }

    override fun onStop() {
        Log.d(TAG, "onStop")
        super.onStop()
        handler.removeCallbacks(updateProgressTask)
        mediaPlayer?.release()
        mediaPlayer = null
    }


    override fun onSaveInstanceState(outState: Bundle) {
        Log.d(TAG, "onSaveInstanceState")
        super.onSaveInstanceState(outState)
        val position = mediaPlayer!!.currentPosition
        outState.putInt(STATE_CURRENT_PLAYING_POSITION, position)
        outState.putBoolean(STATE_IS_PLAYING, mediaPlayer!!.isPlaying)
    }


    //endregion


    //region Initialization and setup methods

    private fun findViews(mainView: View){
        songName = mainView.findViewById(R.id.songNameTextView)
        songCover = mainView.findViewById(R.id.songCoverImageView)
        songCurrentTime = mainView.findViewById(R.id.songCurrentTimeTextView)
        songEndTime = mainView.findViewById(R.id.songDurationTextView)
        songProgressHandler = mainView.findViewById(R.id.songPositionSeekBar)
        songPlayPauseButton = mainView.findViewById(R.id.songPlayPauseButton)
        songPreviousButton = mainView.findViewById(R.id.songPrevButton)
        songNextButton = mainView.findViewById(R.id.songNextButton)
    }

    private fun setupPlayPause() {
        songPlayPauseButton.setOnClickListener(this)
    }

    private fun setupSeekBar(){
        songProgressHandler.setOnSeekBarChangeListener(this)
    }

    private fun setupSongInfoViews(){
        val songDuration = mediaPlayer!!.duration
        updateTimeLabel(songEndTime, songDuration)
        songProgressHandler.max = songDuration

    }


    private fun restoreState(bundle: Bundle){

        val position = bundle.getInt(STATE_CURRENT_PLAYING_POSITION)
        val isPlaying = bundle.getBoolean(STATE_IS_PLAYING)
        mediaPlayer!!.seekTo(position)
        updateProgress()
        mediaPlayerState = if (isPlaying){
            PlayerSate.PLAYING
        } else {
            PlayerSate.STOPPED
        }
    }

    //endregion


    //region OnClickListener

    override fun onClick(v: View?) {
        if (v != null) {
            when (v.id) {
                R.id.songPlayPauseButton -> playPauseClicked()
                R.id.songNextButton -> nextClicked()
                R.id.songPrevButton -> prevClicked()
            }
        }
    }
    //endregion


    //region Click Methods

    private fun playPauseClicked(){
        mediaPlayerState = when (mediaPlayerState) {
            PlayerSate.PLAYING -> PlayerSate.STOPPED
            PlayerSate.STOPPED -> PlayerSate.PLAYING
        }
    }

    private fun prevClicked(){
        throw NotImplementedError()
    }

    private fun nextClicked(){
        throw NotImplementedError()
    }
    //endregion

    private fun updateState(){
        when (mediaPlayerState){
            PlayerSate.PLAYING -> {
                mediaPlayer?.start()
                songPlayPauseButton.text = getString(R.string.music_player_pause_title)
            }
            PlayerSate.STOPPED -> {
                mediaPlayer?.pause()
                songPlayPauseButton.text = getString(R.string.music_player_play_title)
            }
        }
    }

    private fun updateProgress(){
        val currentProgress = mediaPlayer!!.currentPosition
        updateTimeLabel(songCurrentTime, currentProgress)
        songProgressHandler.progress = mediaPlayer!!.currentPosition

    }

    private fun updateTimeLabel(timeLabel: TextView, progress: Int) {
        timeLabel.text = TIME_FORMATTER.format(Date(progress.toLong()))
    }


    //region MediaPlayer.OnPreparedListener
    override fun onPrepared(mp: MediaPlayer?) {
        Log.d(TAG, "onPreparedMediaPlayer, duration " + mediaPlayer!!.duration)
        setupSongInfoViews()
        updateProgressTask.run()
    }
    //endregion

    //region SeekBar.OnSeekBarChangeListener

    override fun onProgressChanged(seekBar: SeekBar?, progress: Int, fromUser: Boolean) {
        updateTimeLabel(songCurrentTime, progress)
    }

    override fun onStartTrackingTouch(seekBar: SeekBar?) {

    }

    override fun onStopTrackingTouch(seekBar: SeekBar?) {
        updateTimeLabel(songCurrentTime, seekBar!!.progress)
        mediaPlayer!!.seekTo(seekBar!!.progress)
    }
    //endregion
}