Android: Kotlin TypeCastException: null kann nicht auf Nicht-Null-Typ umgewandelt werden kotlin.String

Question

Ich bin neu in Kotlin und ich versuche, eine Musik-App zu entwickeln.

Ich bekomme diesen Fehler, den ich nicht lösen kann. Wenn ich meine App öffne, wird die Songliste angezeigt. Wenn ich auf einen Song klicke, wird er auf den aktuellen Bildschirm umgeleitet, aber beim Klicken auf den nächsten oder vorherigen Button stürzt meine App ab.

Das Logcat gibt einen TypeCast-Fehler, den ich nicht verstehe.

Der Kodex ist unter:

class SongPlayingFragment : Fragment() { 

var myActivity: Activity? = null 
var mediaplayer: MediaPlayer? = null 
var startTimeText: TextView? = null 
var endTimeText: TextView? = null 
var playpauseImageButton: ImageButton? = null 
var previousImageButton: ImageButton? = null 
var nextImageButton: ImageButton? = null 
var loopImageButton: ImageButton? = null 
var seekbar: SeekBar? = null 
var songArtistView: TextView? = null 
var songTitleView: TextView? = null 
var shuffleImageButton: ImageButton? = null 
var currentPosition: Int = 0 
var fetchSongs: ArrayList<Songs>? = null 
var currentSongHelper: CurrentSongHelper? = null 
var audioVisualization: AudioVisualization? = null 
var g1view: GLAudioVisualizationView? = null 



object Staticated { 
    var MY_PREFS_SHUFFLE = "Shuffle Feature" 
    var MY_PREFS_LOOP = "Loop Feature" 
} 



var updateSongTime = object : Runnable { 
    override fun run() { 
     val getcurrent = mediaplayer?.currentPosition 
     startTimeText?.setText(String.format("%d:%d", 
       TimeUnit.MILLISECONDS.toMinutes(getcurrent?.toLong() as Long), 
       TimeUnit.MILLISECONDS.toSeconds(getcurrent?.toLong() as Long) - 
         TimeUnit.MILLISECONDS.toSeconds(TimeUnit.MILLISECONDS.toMinutes(getcurrent?.toLong() as Long) 
         ))) 
     seekbar?.setProgress(getcurrent?.toInt() as Int) 
     Handler().postDelayed(this, 1000) 
    } 
} 

override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, 
          savedInstanceState: Bundle?): View? { 

    var view = inflater!!.inflate(R.layout.fragment_song_playing, container, false) 
    seekbar = view?.findViewById(R.id.seekBar) 
    startTimeText = view?.findViewById(R.id.startTime) 
    endTimeText = view?.findViewById(R.id.endTime) 
    playpauseImageButton = view?.findViewById(R.id.playPauseButton) 
    nextImageButton = view?.findViewById(R.id.nextButton) 
    previousImageButton = view?.findViewById(R.id.previousButton) 
    loopImageButton = view?.findViewById(R.id.LoopButton) 
    shuffleImageButton = view?.findViewById(R.id.shuffleButton) 
    songArtistView = view?.findViewById(R.id.songArtist) 
    songTitleView = view?.findViewById(R.id.songTitle) 
    g1view = view?.findViewById(R.id.visualizer_view) 


    return view 
} 

override fun onViewCreated(view: View?, savedInstanceState: Bundle?) { 
    super.onViewCreated(view, savedInstanceState) 
    audioVisualization = g1view as AudioVisualization 
} 

override fun onAttach(context: Context?) { 
    super.onAttach(context) 
    myActivity = context as Activity 
} 

override fun onAttach(activity: Activity?) { 
    super.onAttach(activity) 
    myActivity = activity 
} 

override fun onResume() { 
    super.onResume() 
    audioVisualization?.onResume() 
} 

override fun onPause() { 
    audioVisualization?.onPause() 
    super.onPause() 
} 

override fun onDestroyView() { 
    audioVisualization?.release() 
    super.onDestroyView() 
} 

override fun onActivityCreated(savedInstanceState: Bundle?) { 
    super.onActivityCreated(savedInstanceState) 


    currentSongHelper = CurrentSongHelper() 
    currentSongHelper?.isPlaying = true 
    currentSongHelper?.isLoop = false 
    currentSongHelper?.isShuffle = false 
    var path: String? = null 
    var songTitle: String? = null 
    var songArtist: String? = null 
    var songId: Long = 0 
    try { 
     path = arguments.getString("path") 
     songTitle = arguments.getString("songTitle") 
     songArtist = arguments.getString("songArtist") 
     songId = arguments.getInt("songId").toLong() 
     currentPosition = arguments.getInt("songPosition") 
     fetchSongs = arguments.getParcelableArrayList("songData") 

     currentSongHelper?.songPath = path 
     currentSongHelper?.songTitle = songTitle 
     currentSongHelper?.songArtist = songArtist 
     currentSongHelper?.songId = songId 
     currentSongHelper?.currentPosition = currentPosition 

     updateTextViews(currentSongHelper?.songTitle as String, currentSongHelper?.songArtist as String) 
    } catch(e: Exception) { 
     e.printStackTrace() 
    } 
    mediaplayer = MediaPlayer() 
    mediaplayer?.setAudioStreamType(AudioManager.STREAM_MUSIC) 
    try { 
     mediaplayer?.setDataSource(myActivity, Uri.parse(path)) 
     mediaplayer?.prepare() 
    } catch (e: Exception) { 
     e.printStackTrace() 
    } 

    mediaplayer?.start() 
    processInformation(mediaplayer as MediaPlayer) 
    if (currentSongHelper?.isPlaying as Boolean) { 
     playpauseImageButton?.setBackgroundResource(R.drawable.pause_icon) 
    } else { 
     playpauseImageButton?.setBackgroundResource(R.drawable.play_icon) 
    } 
    mediaplayer?.setOnCompletionListener { 
     onSongComplete() 

    } 
    clickHandler() 
    var visualizationHandler = DbmHandler.Factory.newVisualizerHandler(myActivity as Context, 0) 
    audioVisualization?.linkTo(visualizationHandler) 

    var prefsForShuffle = myActivity?.getSharedPreferences(Staticated.MY_PREFS_SHUFFLE, Context.MODE_PRIVATE) 
    var isShuffleAllowed = prefsForShuffle?.getBoolean("feature", false) 
    if (isShuffleAllowed as Boolean) { 
     currentSongHelper?.isShuffle = true 
     currentSongHelper?.isLoop = false 
     shuffleImageButton?.setBackgroundResource(R.drawable.shuffle_icon) 

     loopImageButton?.setBackgroundResource(R.drawable.loop_white_icon) 
    } else { 
     currentSongHelper?.isShuffle = false 
     shuffleImageButton?.setBackgroundResource(R.drawable.shuffle_white_icon) 
    } 
    var prefsForLoop = myActivity?.getSharedPreferences(Staticated.MY_PREFS_SHUFFLE, Context.MODE_PRIVATE) 
    var isLoopAllowed = prefsForShuffle?.getBoolean("feature", false) 
    if (isLoopAllowed as Boolean) { 
     currentSongHelper?.isShuffle = false 
     currentSongHelper?.isLoop = true 
     shuffleImageButton?.setBackgroundResource(R.drawable.shuffle_white_icon) 

     loopImageButton?.setBackgroundResource(R.drawable.loop_icon) 
    } else { 
     loopImageButton?.setBackgroundResource(R.drawable.loop_white_icon) 
     currentSongHelper?.isLoop = false 

    } 
enter code here 
} 

fun clickHandler() { 



    shuffleImageButton?.setOnClickListener({ 
     var editorShuffle = myActivity?.getSharedPreferences(Staticated.MY_PREFS_SHUFFLE, Context.MODE_PRIVATE)?.edit() 
     var editorLoop = myActivity?.getSharedPreferences(Staticated.MY_PREFS_LOOP, Context.MODE_PRIVATE)?.edit() 
     if (currentSongHelper?.isShuffle as Boolean) { 
      shuffleImageButton?.setBackgroundResource(R.drawable.shuffle_white_icon) 
      currentSongHelper?.isShuffle = false 
      editorShuffle?.putBoolean("feature", false) 
      editorShuffle?.apply() 
     } else { 
      currentSongHelper?.isShuffle = true 
      currentSongHelper?.isLoop = false 
      shuffleImageButton?.setBackgroundResource(R.drawable.shuffle_icon) 
      loopImageButton?.setBackgroundResource(R.drawable.loop_white_icon) 
      editorShuffle?.putBoolean("feature", true) 
      editorShuffle?.apply() 
      editorLoop?.putBoolean("feature", false) 
      editorLoop?.apply() 
     } 
    }) 
    nextImageButton?.setOnClickListener({ 
     currentSongHelper?.isPlaying = true 
     if (currentSongHelper?.isShuffle as Boolean) { 
      playNext("PlayNextLikeNormalShuffle") 
     } else { 
      playNext("PlayNextNormal") 
     } 
    }) 
    previousImageButton?.setOnClickListener({ 
     currentSongHelper?.isPlaying = true 
     if (currentSongHelper?.isLoop as Boolean) { 
      loopImageButton?.setBackgroundResource(R.drawable.loop_white_icon) 
     } 
     playPrevious() 
    }) 
    loopImageButton?.setOnClickListener({ 
     var editorShuffle = myActivity?.getSharedPreferences(Staticated.MY_PREFS_SHUFFLE, Context.MODE_PRIVATE)?.edit() 
     var editorLoop = myActivity?.getSharedPreferences(Staticated.MY_PREFS_LOOP, Context.MODE_PRIVATE)?.edit() 
     if (currentSongHelper?.isLoop as Boolean) { 
      currentSongHelper?.isLoop = false 
      loopImageButton?.setBackgroundResource(R.drawable.loop_white_icon) 
      editorLoop?.putBoolean("feature", false) 
      editorLoop?.apply() 
     } else { 
      currentSongHelper?.isLoop = true 
      currentSongHelper?.isShuffle = false 
      loopImageButton?.setBackgroundResource(R.drawable.loop_icon) 
      shuffleImageButton?.setBackgroundResource(R.drawable.shuffle_white_icon) 
      editorShuffle?.putBoolean("feature", false) 
      editorShuffle?.apply() 
      editorLoop?.putBoolean("feature", true) 
      editorLoop?.apply() 
     } 
    }) 
    playpauseImageButton?.setOnClickListener({ 
     if (mediaplayer?.isPlaying as Boolean) { 
      mediaplayer?.pause() 
      currentSongHelper?.isPlaying = false 
      playpauseImageButton?.setBackgroundResource(R.drawable.play_icon) 
     } else { 
      mediaplayer?.start() 
      currentSongHelper?.isPlaying = true 
      playpauseImageButton?.setBackgroundResource(R.drawable.pause_icon) 
     } 

    }) 

} 

fun playNext(check: String) { 
    if (check.equals("PlayNextNormal", true)) { 
     currentPosition = currentPosition + 1 

    } else if (check.equals("PlayNextLikeNormalShuffle", true)) { 
     var randomObject = Random() 
     var randomPosition = randomObject.nextInt(fetchSongs?.size?.plus(1) as Int) 
     currentPosition = randomPosition 

    } 
    if (currentPosition == fetchSongs?.size) { 
     currentPosition = 0 
    } 
    currentSongHelper?.isLoop = false 
    var nextSong = fetchSongs?.get(currentPosition) 
    currentSongHelper?.songPath = nextSong?.songData 
    currentSongHelper?.songTitle = nextSong?.songTitle 
    currentSongHelper?.currentPosition = currentPosition 
    currentSongHelper?.songId = nextSong?.songId as Long 

    updateTextViews(currentSongHelper?.songTitle as String, currentSongHelper?.songArtist as String) 
    mediaplayer?.reset() 
    try { 
     mediaplayer?.setDataSource(myActivity, Uri.parse(currentSongHelper?.songPath)) 
     mediaplayer?.prepare() 
     mediaplayer?.start() 
     processInformation(mediaplayer as MediaPlayer) 
    } catch (e: Exception) { 
     e.printStackTrace() 
    } 


} 

fun playPrevious() { 
    currentPosition = currentPosition - 1 

    if (currentPosition == -1) { 
     currentPosition = 0 
    } 
    if (currentSongHelper?.isPlaying as Boolean) { 
     playpauseImageButton?.setBackgroundResource(R.drawable.pause_icon) 
    } else { 
     playpauseImageButton?.setBackgroundResource(R.drawable.play_icon) 
    } 
    currentSongHelper?.isLoop = false 
    var nextSong = fetchSongs?.get(currentPosition) 
    currentSongHelper?.songPath = nextSong?.songData 
    currentSongHelper?.songTitle = nextSong?.songTitle 
    currentSongHelper?.currentPosition = currentPosition 
    currentSongHelper?.songId = nextSong?.songId as Long 

    updateTextViews(currentSongHelper?.songTitle as String, currentSongHelper?.songArtist as String) 

    mediaplayer?.reset() 
    try { 
     mediaplayer?.setDataSource(activity, Uri.parse(currentSongHelper?.songPath)) 
     mediaplayer?.prepare() 
     mediaplayer?.start() 
     processInformation(mediaplayer as MediaPlayer) 
    } catch (e: Exception) { 
     e.printStackTrace() 
    } 

} 

fun onSongComplete() { 
    if (currentSongHelper?.isShuffle as Boolean) { 
     playNext("PlayNextLikeNormalShuffle") 
     currentSongHelper?.isPlaying = true 
    } else { 
     if (currentSongHelper?.isLoop as Boolean) { 
      currentSongHelper?.isPlaying = true 
      var nextSong = fetchSongs?.get(currentPosition) 

      currentSongHelper?.songTitle = nextSong?.songTitle 
      currentSongHelper?.songPath = nextSong?.songData 
      currentSongHelper?.currentPosition = currentPosition 
      currentSongHelper?.songId = nextSong?.songId as Long 

      updateTextViews(currentSongHelper?.songTitle as String, currentSongHelper?.songArtist as String) 
      mediaplayer?.reset() 
      try { 
       mediaplayer?.setDataSource(myActivity, Uri.parse(currentSongHelper?.songPath)) 
       mediaplayer?.prepare() 
       mediaplayer?.start() 

      } catch (e: Exception) { 
       e.printStackTrace() 
      } 

     } else { 
      playNext("PlayNextNormal") 
      currentSongHelper?.isPlaying = true 
     } 
    } 

} 

fun updateTextViews(songtitle: String, songArtist: String) { 
    songTitleView?.setText(songtitle) 
    songArtistView?.setText(songArtist) 
} 

fun processInformation(mediaPlayer: MediaPlayer) { 
    val finalTime = mediaPlayer.duration 
    val startTime = mediaPlayer.currentPosition 
    seekbar?.max = finalTime 
    startTimeText?.setText(String.format("%d: %d", 
      TimeUnit.MILLISECONDS.toMinutes(startTime.toLong()), 
      TimeUnit.MILLISECONDS.toSeconds(startTime.toLong()) - 
        TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(startTime?.toLong())) 
    )) 
    endTimeText?.setText(String.format("%d:%d", 
      TimeUnit.MILLISECONDS.toMinutes(finalTime.toLong()), 
      TimeUnit.MILLISECONDS.toSeconds(finalTime.toLong()) - 
        TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(finalTime?.toLong()))) 
    ) 
    seekbar?.setProgress(startTime) 
    Handler().postDelayed(updateSongTime, 1000) 
} 

}

LOGS:

12-07 20:30:27.447 28230-28230/com.example.sanjanaadmin.echo E/AndroidRuntime: FATAL EXCEPTION: main 
    Process: com.example.sanjanaadmin.echo, PID: 28230 
    kotlin.TypeCastException: null cannot be cast to non-null type kotlin.String 
     at com.example.sanjanaadmin.echo.fragments.SongPlayingFragment.playNext(SongPlayingFragment.kt:314) 
     at com.example.sanjanaadmin.echo.fragments.SongPlayingFragment$clickHandler$2.onClick(SongPlayingFragment.kt:250) 
     at android.view.View.performClick(View.java:5268) 
     at android.view.View$PerformClick.run(View.java:21550) 
     at android.os.Handler.handleCallback(Handler.java:822) 
     at android.os.Handler.dispatchMessage(Handler.java:104) 
     at android.os.Looper.loop(Looper.java:207) 
     at android.app.ActivityThread.main(ActivityThread.java:5811) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:681) 

Answer 1

Sie versuchen, einen Nullable-Wert von einem safe call (?.) auf die nicht-Null-Typ String hergestellt zu werfen:

currentSongHelper?.songTitle as String 

^{(und einige weitere Orte)}

Diese Umwandlung schlägt fehl, wenn der Wert null ist. Um dies zu beheben, werfen auf den Nullable Type statt String?:

currentSongHelper?.songTitle as String? 

^{(fix die anderen solchen Fällen auch)}

Answer 2

können Sie auch versuchen, eine dieser Lösungen:

• Standardwert bereitstellen

  currentSongHelper?.songTitle?:"default song title"

• Wurf Inline Ausnahme

  currentSongHelper?.songTitle?: throw NullpointerException("title is null")

• sicher Guss

  currentSongHelper?.songTitle as? String