如何使用Java在Android上正确启动音乐服务

音乐服务

我一直在努力学习这方面的教程，但似乎无法启动音乐服务。我错过了什么

public class MusicService extends Service implements
        OnPreparedListener, MediaPlayer.OnErrorListener,
        MediaPlayer.OnCompletionListener {

    //media player
    private MediaPlayer player;
    //song list
    private ArrayList<song> songs;
    //current position
    private int songPosn;

    public void onCreate(){
        //create the service
        //create the service
        super.onCreate();
        //initialize position
        songPosn    = 0;
        //create player
        player      = new MediaPlayer();
        if (player == null){ Log.e("error", "mediaPlayer is null");}
        initMusicPlayer();
    }

    public void setList(ArrayList<song> theSongs){
        songs=theSongs;
    }

    public class MusicBinder extends Binder {
        MusicService getService() {
            return MusicService.this;
        }
    }

    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);
    }

    @Override
    public IBinder onBind(Intent arg0) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void onCompletion(MediaPlayer mp) {

    }

    @Override
    public boolean onError(MediaPlayer mp, int i, int i1) {

        return false;
    }

    @Override
    public void onPrepared(MediaPlayer mp){
        mp.start();
    }

    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();
    }

    public void setSong(int songIndex){
        songPosn=songIndex;
    }

}

---

我强烈建议切换到一个新的教程，并使用一种技术，例如使您的音乐服务和用户界面工作变得更加轻松。@ianhanniballake让我来看看。@ianhanniballake查看了这篇文章。我找不到任何关于MediaBrowserServiceCompat的教程。这是关于MediaBrowserServiceCompat的教程：）我强烈建议切换到一个新的教程，并使用一种技术，例如使使用音乐服务和用户界面变得更容易。@ianhanniballake让我检查一下。@ianhanniballake检查了文章我找不到任何关于MediaBrowserServiceCompat的教程。这是关于MediaBrowserServiceCompat的教程：）

import android.content.ComponentName;
import android.content.ContentResolver;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.ServiceConnection;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.os.IBinder;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.NavigationView;
import android.support.design.widget.Snackbar;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ListView;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import com.auxiline.audio.*;

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    private ArrayList<song> songList;
    private ListView songView;
    private MusicService musicSrv;
    private Intent playIntent;
    private boolean musicBound=false;

    public MainActivity(){
       //dialogBox();
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        //dialogBox();
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        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);

    }

    public void dialogBox() {
        AlertDialog.Builder builder1 = new AlertDialog.Builder(this);
        builder1.setMessage("Write your message here.");
        builder1.setCancelable(true);

        builder1.setPositiveButton(
                "Yes",
                new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int id) {
                        dialog.cancel();
                    }
                });

        builder1.setNegativeButton(
                "No",
                new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int id) {
                        dialog.cancel();
                    }
                });

        AlertDialog alert11 = builder1.create();
        alert11.show();
    }

    //connect to the service
    private ServiceConnection musicConnection = new ServiceConnection(){

        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            dialogBox();
            MusicService.MusicBinder binder = (MusicService.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);
        }
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.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);

    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_camera) {
            // Handle the camera action
        } else if (id == R.id.nav_gallery) {

        } else if (id == R.id.nav_slideshow) {

        } else if (id == R.id.nav_manage) {

        } else if (id == R.id.nav_share) {

        } else if (id == R.id.nav_send) {

        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

    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);

        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());
        }

    }

    public void songPicked(View view){
        if (musicSrv == null){
            throw new NullPointerException("Music service is not binded!");
            //Log.e("error", "mediaPlayer is null");
        }
        musicSrv.setSong(Integer.parseInt(view.getTag().toString()));
        musicSrv.playSong();
    }


    @Override
    protected void onDestroy() {
        stopService(playIntent);
        musicSrv=null;
        super.onDestroy();
    }
}

04-21 06:39:16.836 18920-18920/com.auxiline.audio E/AndroidRuntime: FATAL EXCEPTION: main
                                                                    Process: com.auxiline.audio, PID: 18920
                                                                    java.lang.IllegalStateException: Could not execute method of the activity
                                                                        at android.view.View$1.onClick(View.java:3969)
                                                                        at android.view.View.performClick(View.java:4633)
                                                                        at android.view.View$PerformClick.run(View.java:19330)
                                                                        at android.os.Handler.handleCallback(Handler.java:733)
                                                                        at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                        at android.os.Looper.loop(Looper.java:157)
                                                                        at android.app.ActivityThread.main(ActivityThread.java:5356)
                                                                        at java.lang.reflect.Method.invokeNative(Native Method)
                                                                        at java.lang.reflect.Method.invoke(Method.java:515)
                                                                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
                                                                        at dalvik.system.NativeStart.main(Native Method)
                                                                     Caused by: java.lang.reflect.InvocationTargetException
                                                                        at java.lang.reflect.Method.invokeNative(Native Method)
                                                                        at java.lang.reflect.Method.invoke(Method.java:515)
                                                                        at android.view.View$1.onClick(View.java:3964)
                                                                        at android.view.View.performClick(View.java:4633) 
                                                                        at android.view.View$PerformClick.run(View.java:19330) 
                                                                        at android.os.Handler.handleCallback(Handler.java:733) 
                                                                        at android.os.Handler.dispatchMessage(Handler.java:95) 
                                                                        at android.os.Looper.loop(Looper.java:157) 
                                                                        at android.app.ActivityThread.main(ActivityThread.java:5356) 
                                                                        at java.lang.reflect.Method.invokeNative(Native Method) 
                                                                        at java.lang.reflect.Method.invoke(Method.java:515) 
                                                                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265) 
                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081) 
                                                                        at dalvik.system.NativeStart.main(Native Method) 
                                                                     Caused by: java.lang.NullPointerException: Music service is not binded!
                                                                        at com.auxiline.audio.MainActivity.songPicked(MainActivity.java:238)
                                                                        at java.lang.reflect.Method.invokeNative(Native Method) 
                                                                        at java.lang.reflect.Method.invoke(Method.java:515) 
                                                                        at android.view.View$1.onClick(View.java:3964) 
                                                                        at android.view.View.performClick(View.java:4633) 
                                                                        at android.view.View$PerformClick.run(View.java:19330) 
                                                                        at android.os.Handler.handleCallback(Handler.java:733) 
                                                                        at android.os.Handler.dispatchMessage(Handler.java:95) 
                                                                        at android.os.Looper.loop(Looper.java:157) 
                                                                        at android.app.ActivityThread.main(ActivityThread.java:5356) 
                                                                        at java.lang.reflect.Method.invokeNative(Native Method) 
                                                                        at java.lang.reflect.Method.invoke(Method.java:515) 
                                                                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265) 
                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081) 
                                                                        at dalvik.system.NativeStart.main(Native Method)