我正在尝试创建一个简单的音乐应用程序，但是当我点击歌曲名称时，应用程序会崩溃，并且会抛出异常。
'Attempt to invoke virtual method Error setting data source java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object referenceat android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:117) at com.studios.debug.musicplayer.MusicService.playSong(MusicService.java:87) at com.studios.debug.musicplayer.RecyclerViewAdapter$MyViewHolder$1.onClick(RecyclerViewAdapter.java:58)
at android.view.View.performClick(View.java:5207)
at android.view.View$PerformClick.run(View.java:21177)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5438)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)
06-29 17:40:48.070 20284-20284/com.studios.debug.musicplayer E/AndroidRuntime: FATAL EXCEPTION: main Process: com.studios.debug.musicplayer, PID: 20284 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.media.MediaPlayer.prepareAsync()' on a null object reference at com.studios.debug.musicplayer.MusicService.playSong(MusicService.java:91) at com.studios.debug.musicplayer.RecyclerViewAdapter$MyViewHolder$1.onClick(RecyclerViewAdapter.java:58) at android.view.View.performClick(View.java:5207) at android.view.View$PerformClick.run(View.java:21177) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5438) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)
on a null object reference'
这是我的代码： MusicService.java
public class MusicService extends Service implements MediaPlayer.OnPreparedListener, MediaPlayer.OnErrorListener, MediaPlayer.OnCompletionListener {
private final IBinder musicBind = new MusicBinder();
private MediaPlayer player;
private ArrayList<Song> songs;
private int songposition;
@Override
public void onCreate() {
super.onCreate();
songposition = 0;
player = new MediaPlayer();
initMusicPlayer();
}
public void initMusicPlayer() {
player.setWakeMode(getApplicationContext(), PowerManager.PARTIAL_WAKE_LOCK);
player.setAudioStreamType(AudioManager.STREAM_MUSIC);
player.setOnPreparedListener(this);
player.setOnCompletionListener(this);
player.setOnErrorListener(this);
}
public void setList(ArrayList<Song> theSong) {
Log.e("Test", "" + theSong.size());
this.songs = theSong;
}
@Override
public boolean onUnbind(Intent intent) {
return false;
}
@Nullable
@Override
public IBinder onBind(Intent intent) {
return musicBind;
}
@Override
public void onCompletion(MediaPlayer mp) {
}
@Override
public boolean onError(MediaPlayer mp, int what, int extra) {
/* mp.reset();*/
return false;
}
@Override
public void onPrepared(MediaPlayer mp) {
mp.start();
}
public void playSong(ArrayList<Song> songs1) {
Log.e("Test1", "" + songs1.size());
Song playSong = songs1.get(songposition);
long currSong = playSong.getID();
Uri trackUri = ContentUris.withAppendedId(MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, currSong);
try {
player.setDataSource(getApplicationContext(), trackUri);
} catch (Exception e) {
Log.e("MUSIC SERVICE", "Error setting data source", e);
}
player.prepareAsync();
}
public void setSong(int songIndex) {
songposition = songIndex;
}
public class MusicBinder extends Binder {
MusicService getService() {
return MusicService.this;
}
}
}
MainActivity.java
public class MainActivity extends AppCompatActivity {
private ArrayList<Song> songArrayList;
private RecyclerView recyclerView;
private RecyclerViewAdapter recyclerViewAdapter;
private MusicService musicSrv;
private Intent playIntent;
private MediaPlayer player;
private boolean musicBound = false;
private ServiceConnection musicConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
MusicBinder binder = (MusicBinder) service;
musicSrv = binder.getService();
musicSrv.setList(songArrayList);
musicBound = true;
}
@Override
public void onServiceDisconnected(ComponentName name) {
musicBound = false;
}
};
@Override
protected void onStart() {
super.onStart();
if (playIntent == null) {
playIntent = new Intent(this, MusicService.class);
bindService(playIntent, musicConnection, Context.BIND_AUTO_CREATE);
startService(playIntent);
}
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
requestPermissions(new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, 1);
return;
}
}
recyclerView = (RecyclerView) findViewById(R.id.songs_lists);
songArrayList = new ArrayList<Song>();
getSongList();
Collections.sort(songArrayList, new Comparator<Song>() {
@Override
public int compare(Song o1, Song o2) {
return o1.getTitle().compareTo(o2.getTitle());
}
});
recyclerViewAdapter = new RecyclerViewAdapter(MainActivity.this, songArrayList);
RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
recyclerView.setLayoutManager(mLayoutManager);
recyclerView.addItemDecoration(new SimpleDivider(MainActivity.this));
recyclerView.setAdapter(recyclerViewAdapter);
}
public void getSongList() {
ContentResolver contentResolver = getContentResolver();
Uri musicUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
Cursor musicCursor = contentResolver.query(musicUri, null, null, null, null);
Log.e("test",""+musicCursor.getCount());
if (musicCursor != null && musicCursor.moveToFirst()) {
do {
long thisId = musicCursor.getLong(musicCursor.getColumnIndex(MediaStore.Audio.Media._ID));
String thisTitle = musicCursor.getString(musicCursor.getColumnIndex(MediaStore.Audio.Media.TITLE));
String thisArtist = musicCursor.getString(musicCursor.getColumnIndex(MediaStore.Audio.Media.ARTIST));
songArrayList.add(new Song(thisId, thisTitle, thisArtist));
} while (musicCursor.moveToNext());
musicCursor.close();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.main, menu);
return true;
}
@Override
protected void onDestroy() {
if (musicBound) unbindService(musicConnection);
stopService(playIntent);
musicSrv = null;
/* player.stop();
player.release();*/
super.onDestroy();
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.action_shuffle:
break;
case R.id.action_end:
stopService(playIntent);
musicSrv = null;
System.exit(0);
break;
}
return super.onOptionsItemSelected(item);
}
}
RecyclerViewAdapter.java
public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.MyViewHolder> {
Context context;
private ArrayList<Song> songs;
private MusicService musicSrv;
public RecyclerViewAdapter(Context c, ArrayList<Song> songs1) {
this.songs = songs1;
Log.e("Test", "" + songs.size());
this.context = c;
}
@Override
public RecyclerViewAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(context).inflate(R.layout.row_list, parent, false);
return new MyViewHolder(view);
}
@Override
public void onBindViewHolder(RecyclerViewAdapter.MyViewHolder holder, int position) {
Song song = songs.get(position);
holder.title.setText(song.getTitle());
holder.artist.setText(song.getArtist());
}
@Override
public int getItemCount() {
return songs.size();
}
public class MyViewHolder extends RecyclerView.ViewHolder {
public TextView title, artist;
public MyViewHolder(View itemView) {
super(itemView);
title = (TextView) itemView.findViewById(R.id.song_title);
artist = (TextView) itemView.findViewById(R.id.song_artist);
itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
musicSrv=new MusicService();
musicSrv.setSong(getLayoutPosition());
musicSrv.playSong(songs);
}
});
}
}
}
答案 0 :(得分：2)
您无法通过创建新对象来启动服务： 你在做什么：
// PIC S9(03) COMP-3.
protected static PackedDecimalAsBigDecimalField epcutb_org = factory.getPackedDecimalAsBigDecimalField(3, 0, true);
// PIC S9(03) COMP-3.
protected static PackedDecimalAsBigDecimalField epcutb_curr = factory.getPackedDecimalAsBigDecimalField(3, 0, true);
// PIC S9(06) COMP-3.
protected static PackedDecimalAsBigDecimalField epcutb_org_curr = factory.getPackedDecimalAsBigDecimalField(6, 0, true);
public void setEpcutb_org(BigDecimal utb_org) { //utb_org==867
epcutb_org.putBigDecimal(utb_org ,epcutbytes);
}
public void setEpcutb_curr(BigDecimal utb_curr) { // utb_curr=840
epcutb_curr.putBigDecimal(utb_curr ,epcutbytes);
}
public BigDecimal getEpcutb_org_curr() {
epcutb_org_curr.setOffset(epcutb_org.getOffset()); // here concatenation is happening for epcutb_org and epcutb_curr so the return value should be "867840" but the return value i am getting is "8682840"
return epcutb_org_curr.getBigDecimal(epcutbytes);
}
并且在playSong方法中，您尝试使用getApplicationContext（），它将为null，因为您需要启动服务而不是创建它的对象，如：
musicSrv=new MusicService();
musicSrv.setSong(getLayoutPosition());
musicSrv.playSong(songs);