我已经在这个圈子里绕了好几天。我正在按照教程创建音乐播放器服务： part 2 of music player tutorial
我认为我已经正确地遵循了它，但是在尝试设置歌曲ID时出现错误，因为该服务尚未正确启动。检查它永远不会调用MusicService类的onBind方法。通常这是由于没有在android清单中正确设置服务。但是，我查看了许多帮助页面，相应地更改了我的服务电话，而且我不认为它是错误的来源。我有什么想法吗？
Android清单：
<uses-permission android:name="android.permission.READ_USER_DICTIONARY" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name"
android:launchMode="singleTop"
android:screenOrientation="portrait" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
<service android:name="mycompany.mediaplayer.MusicService">
</service>
</manifest>
MainActivity.java
package mycompany.mediaplayer;
import android.provider.BaseColumns;
import android.provider.UserDictionary;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.os.IBinder;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.view.MenuItem;
import android.view.View;
import mycompany.mediaplayer.MusicService.MusicBinder;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import android.net.Uri;
import android.content.ContentResolver;
import android.database.Cursor;
import android.widget.ListView;
public class MainActivity extends ActionBarActivity {
private ArrayList<Song> songList;
private ListView songView;
private MusicService musicSrv;
private Intent playIntent;
private boolean musicBound=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);
}
//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;
Log.i("onServiceConnected", "Have called connection");
Log.i("onServiceConnected", String.valueOf(musicSrv));
}
@Override
public void onServiceDisconnected(ComponentName name) {
musicBound = false;
}
};
@Override
protected void onStart() {
super.onStart();
if(playIntent==null){
Log.i("onStart", "Binding service");
playIntent = new Intent(this, MusicService.class);
Log.i("onStart", "Play intent "+String.valueOf(playIntent));
Log.i("onStart", String.valueOf(bindService(playIntent, musicConnection, Context.BIND_AUTO_CREATE)));
startService(playIntent);
}
Log.i("onStart", "Have started the activity");
Log.i("onStart", String.valueOf(musicSrv));
}
@Override
protected void onDestroy() {
stopService(playIntent);
musicSrv=null;
super.onDestroy();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
// //noinspection SimplifiableIfStatement
// if (id == R.id.action_settings) {
// return true;
// }
switch (item.getItemId()) {
case R.id.action_shuffle:
//shuffle
break;
case R.id.action_end:
stopService(playIntent);
musicSrv=null;
System.exit(0);
break;
}
return super.onOptionsItemSelected(item);
}
public void songPicked(View view){
Log.i("songPicked", String.valueOf(musicSrv));
Log.i("songPicked", String.valueOf(Integer.parseInt(view.getTag().toString())));
int song_number = Integer.parseInt(view.getTag().toString());
Log.i("songPicked", String.valueOf(song_number));
musicSrv.setSong(song_number);
musicSrv.playSong();
}
public void getSongList() {
//retrieve song info
ContentResolver musicResolver = getContentResolver();
Uri musicUri = android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
Cursor musicCursor = musicResolver.query(musicUri, null, null, null, null);
Log.i("MusicRetriever", "Query finished. " + (musicCursor == null ? "Returned NULL." : "Returned a cursor."));
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));
//Log.i("MusicRetriever", "Added song" + thisTitle);
}
while (musicCursor.moveToNext());
}
}
}
MusicService.java
package mycompany.mediaplayer;
/**
* Created by Neill on 28/02/2016.
*/
import java.util.ArrayList;
import android.app.Service;
import android.content.ContentUris;
import android.content.Intent;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.net.Uri;
import android.os.Binder;
import android.os.IBinder;
import android.os.PowerManager;
import android.util.Log;
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();
public void onCreate(){
//create the service
super.onCreate();
//initialize position
songPosn=0;
//create player
Log.i("onCreate", "Creating service");
player = new MediaPlayer();
initMusicPlayer();
}
public void onCompletion(MediaPlayer mp) {
}
public boolean onError(MediaPlayer mp, int a, int b) {
return false;
}
public void initMusicPlayer(){
//set player properties
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;
}
}
@Override
public IBinder onBind(Intent intent) {
Log.i("onBind", "Returning bind");
return musicBind;
}
@Override
public boolean onUnbind(Intent intent){
player.stop();
player.release();
return false;
}
public void playSong(){
//play a song
player.reset();
//get song
Song playSong = songs.get(songPosn);
//get id
long currSong = playSong.getID();
//set uri
Uri trackUri = ContentUris.withAppendedId(
android.provider.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();
}
@Override
public void onPrepared(MediaPlayer mp) {
//start playback
mp.start();
}
public void setSong(int songIndex){
songPosn=songIndex;
}
}
最后是logcat：
03-17 21:55:43.986 29835-29835/? I/art: Late-enabling -Xcheck:jni
03-17 21:55:44.028 29835-29835/? W/ResourceType: Found multiple library tables, ignoring...
03-17 21:55:44.034 29835-29835/? W/ResourceType: Found multiple library tables, ignoring...
03-17 21:55:44.038 29835-29835/? W/ResourceType: Found multiple library tables, ignoring...
03-17 21:55:44.243 29835-29835/mycompany.mediaplayer I/MusicRetriever: Query finished. Returned a cursor.
03-17 21:55:44.308 29835-29835/mycompany.mediaplayer I/onStart: Binding service
03-17 21:55:44.308 29835-29835/mycompany.mediaplayer I/onStart: Play intent Intent { cmp=mycompany.mediaplayer/.MusicService }
03-17 21:55:44.310 29835-29835/mycompany.mediaplayer I/onStart: false
03-17 21:55:44.310 29835-29835/mycompany.mediaplayer I/onStart: Have started the activity
03-17 21:55:44.310 29835-29835/mycompany.mediaplayer I/onStart: null
03-17 21:55:44.322 29835-29864/mycompany.mediaplayer D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true
03-17 21:55:44.337 29835-29835/mycompany.mediaplayer D/Atlas: Validating map...
03-17 21:55:44.399 29835-29864/mycompany.mediaplayer I/Adreno-EGL: <qeglDrvAPI_eglInitialize:410>: EGL 1.4 QUALCOMM build: AU_LINUX_ANDROID_LA.BF.1.1.1_RB1.05.01.00.042.030_msm8226_LA.BF.1.1.1_RB1__release_AU ()
OpenGL ES Shader Compiler Version: E031.25.03.06
Build Date: 06/10/15 Wed
Local Branch:
Remote Branch: quic/LA.BF.1.1.1_rb1.24
Local Patches: NONE
Reconstruct Branch: AU_LINUX_ANDROID_LA.BF.1.1.1_RB1.05.01.00.042.030 + 6151be1 + NOTHING
03-17 21:55:44.401 29835-29864/mycompany.mediaplayer I/OpenGLRenderer: Initialized EGL, version 1.4
03-17 21:55:44.421 29835-29864/mycompany.mediaplayer D/OpenGLRenderer: Enabling debug mode 0
03-17 21:55:44.780 29835-29835/mycompany.mediaplayer I/Timeline: Timeline: Activity_idle id: android.os.BinderProxy@285dcbce time:12224185
03-17 21:55:46.802 29835-29835/mycompany.mediaplayer I/songPicked: null
03-17 21:55:46.802 29835-29835/mycompany.mediaplayer I/songPicked: 6
03-17 21:55:46.802 29835-29835/mycompany.mediaplayer I/songPicked: 6
03-17 21:55:46.803 29835-29835/mycompany.mediaplayer D/AndroidRuntime: Shutting down VM
03-17 21:55:46.804 29835-29835/mycompany.mediaplayer E/AndroidRuntime: FATAL EXCEPTION: main
Process: mycompany.mediaplayer, PID: 29835
java.lang.IllegalStateException: Could not execute method of the activity
at android.view.View$1.onClick(View.java:4096)
at android.view.View.performClick(View.java:4856)
at android.view.View$PerformClick.run(View.java:19956)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:211)
at android.app.ActivityThread.main(ActivityThread.java:5371)
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:945)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:740)
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$1.onClick(View.java:4091)
at android.view.View.performClick(View.java:4856)
at android.view.View$PerformClick.run(View.java:19956)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:211)
at android.app.ActivityThread.main(ActivityThread.java:5371)
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:945)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:740)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void mycompany.mediaplayer.MusicService.setSong(int)' on a null object reference
at mycompany.mediaplayer.MainActivity.songPicked(MainActivity.java:130)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at android.view.View$1.onClick(View.java:4091)
at android.view.View.performClick(View.java:4856)
at android.view.View$PerformClick.run(View.java:19956)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:211)
at android.app.ActivityThread.main(ActivityThread.java:5371)
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:945)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:740)
03-17 21:55:48.109 29835-29835/mycompany.mediaplayer I/Process: Sending signal. PID: 29835 SIG: 9
提前感谢您的帮助。
答案 0 :(得分：0)
修正了它！
需要一段时间才能追踪，但我的错误是将调用“服务”放在Android清单中的“应用程序”部分之外。向上移动服务线可以解决问题。