我试图调用此方法，但它没有调用
ServiceConnection musicConnection = new ServiceConnection(){ onServiceConnected(ComponentName name, IBinder service)
因为我得到了以下错误。 它在Fragment上运行正常，但是当我尝试在AppCompatActivity上运行它时它无效。
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.kpgames.testmusicplayer.MusicService.setSong(int)' on a null object reference
----------
java.lang.IllegalStateException: Could not execute method of the activity
at android.view.View$1.onClick(View.java:4023)
at android.view.View.performClick(View.java:4783)
at android.view.View$PerformClick.run(View.java:19887)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5290)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:703)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at android.view.View$1.onClick(View.java:4018)
at android.view.View.performClick(View.java:4783)
at android.view.View$PerformClick.run(View.java:19887)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5290)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:703)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.kpgames.testmusicplayer.MusicService.setSong(int)' on a null object reference
at com.kpgames.testmusicplayer.MainActivity.songPicked(MainActivity.java:90)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at android.view.View$1.onClick(View.java:4018)
at android.view.View.performClick(View.java:4783)
at android.view.View$PerformClick.run(View.java:19887)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5290)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:703)
MainActivity.java
public class MainActivity extends AppCompatActivity implements MediaPlayerControl{
private ArrayList<Song> songList;
private ListView songView;
private MusicController controller;
private MusicService musicSrv;
private Intent playIntent;
private boolean musicBound=false;
private boolean paused=false, playbackPaused=false;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
songView = (ListView)findViewById(R.id.song_list);
songList = new ArrayList<Song>();
getSongList();
Collections.sort(songList, new Comparator<Song>(){
public int compare(Song a, Song b){
return a.getTitle().compareTo(b.getTitle());
}
});
SongAdapter songAdt = new SongAdapter(this, songList);
songView.setAdapter(songAdt);
setController();
}
//connect to the service
private ServiceConnection musicConnection = new ServiceConnection(){
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
MusicBinder binder = (MusicBinder)service;
//get service
musicSrv = binder.getService();
//pass list
musicSrv.setList(songList);
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);
//}
}
public void songPicked(View view){
musicSrv.setSong(Integer.parseInt(view.getTag().toString()));
musicSrv.playSong();
if(playbackPaused){
setController();
playbackPaused=false;
}
controller.show(0);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.action_shuffle:
musicSrv.setShuffle();
break;
case R.id.action_end:
stopService(playIntent);
musicSrv=null;
System.exit(0);
break;
}
return super.onOptionsItemSelected(item);
}
@Override
protected void onDestroy() {
stopService(playIntent);
musicSrv=null;
super.onDestroy();
}
public void getSongList() {
ContentResolver musicResolver = getContentResolver();
Uri musicUri = android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
Cursor musicCursor = musicResolver.query(musicUri, null, null, null, null);
if(musicCursor!=null && musicCursor.moveToFirst()){
//get columns
int titleColumn = musicCursor.getColumnIndex
(android.provider.MediaStore.Audio.Media.TITLE);
int idColumn = musicCursor.getColumnIndex
(android.provider.MediaStore.Audio.Media._ID);
int artistColumn = musicCursor.getColumnIndex
(android.provider.MediaStore.Audio.Media.ARTIST);
//add songs to list
do {
long thisId = musicCursor.getLong(idColumn);
String thisTitle = musicCursor.getString(titleColumn);
String thisArtist = musicCursor.getString(artistColumn);
songList.add(new Song(thisId, thisTitle, thisArtist));
}
while (musicCursor.moveToNext());
}
}
private void setController(){
controller = new MusicController(this);
controller.setPrevNextListeners(new View.OnClickListener() {
@Override
public void onClick(View v) {
playNext();
}
}, new View.OnClickListener() {
@Override
public void onClick(View v) {
playPrev();
}
});
controller.setMediaPlayer(this);
controller.setAnchorView(findViewById(R.id.song_list));
controller.setEnabled(true);
}
private void playNext(){
musicSrv.playNext();
if(playbackPaused){
setController();
playbackPaused=false;
}
controller.show(0);
}
private void playPrev(){
musicSrv.playPrev();
if(playbackPaused){
setController();
playbackPaused=false;
}
controller.show(0);
}
@Override
public void start() {
musicSrv.go();
}
@Override
public void pause() {
playbackPaused=true;
musicSrv.pausePlayer();
}
@Override
public int getDuration() {
if(musicSrv!=null && musicBound && musicSrv.isPng())
return musicSrv.getDur();
else return 0;
}
@Override
public int getCurrentPosition() {
if(musicSrv!=null && musicBound && musicSrv.isPng())
return musicSrv.getPosn();
else return 0;
}
@Override
protected void onPause(){
super.onPause();
paused=true;
}
@Override
protected void onResume(){
super.onResume();
if(paused){
setController();
paused=false;
}
}
@Override
protected void onStop() {
controller.hide();
super.onStop();
}
@Override
public void seekTo(int pos) {
musicSrv.seek(pos);
}
@Override
public boolean isPlaying() {
if(musicSrv!=null && musicBound)
return musicSrv.isPng();
return false;
}
@Override
public int getBufferPercentage() {
return 0;
}
@Override
public boolean canPause() {
return true;
}
@Override
public boolean canSeekBackward() {
return true;
}
@Override
public boolean canSeekForward() {
return true;
}
@Override
public int getAudioSessionId() {
return 0;
}
}
这是服务代码
public class MusicService extends Service implements MediaPlayer.OnPreparedListener, MediaPlayer.OnErrorListener, MediaPlayer.OnCompletionListener {
//media player
private MediaPlayer player;
//song list
private ArrayList<Song> songs;
//current position
private int songPosn;
private final IBinder musicBind = new MusicBinder();
private String songTitle = "";
private static final int NOTIFY_ID = 1;
private boolean shuffle = false;
private Random rand;
@Override
public IBinder onBind(Intent intent) {
return musicBind;
}
@Override
public boolean onUnbind(Intent intent) {
player.stop();
player.release();
return false;
}
public void onCreate() {
//create the service
super.onCreate();
//initialize position
songPosn = 0;
//create player
player = new MediaPlayer();
initMusicPlayer();
rand = new Random();
}
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> theSongs) {
songs = theSongs;
}
public class MusicBinder extends Binder {
MusicService getService() {
return MusicService.this;
}
}
谢谢！
答案 0 :(得分：0)
Android为每个服务调用onBind（）方法一次。如果稍后绑定/解除它，则调用方法.onRebind（）