Android：Kotlin TypeCastException：null不能转换为非nulltypes的kotlin.String
我是Kotlin的新手，我正在尝试开发一个音乐应用程序。
我得到这个我无法解决的错误。 当我打开我的应用程序时，歌曲列表显示，点击歌曲重定向到现在显示屏幕，但点击下一个或上一个按钮我的应用程序崩溃。
logcat是一个TypeCast错误，我不明白。
代码如下：
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? = 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) } }
日志：
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)
您试图将安全调用（ ?. ）生成的可空值强制转换为非空types的String ：
currentSongHelper?.songTitle as String
（和更多的地方）
如果该值为空，则该转换将失败。 为了解决这个问题，转换为可空types而不是String? ：
currentSongHelper?.songTitle as String?
（修复其他类似的情况）
您也可以尝试以下解决方案之一：
-
提供默认值
currentSongHelper?.songTitle?:"default song title" -
抛出内联exception
currentSongHelper?.songTitle?: throw NullpointerException("title is null") -
安全演员
currentSongHelper?.songTitle as? String