Question

这行代码在Android工作室中给我带来了麻烦

if(musicSrv!=null &amp;&amp; musicBound &amp;&amp; musicSrv.isPng())

代码来自我发现的教程：Music Player

完整的类代码是：

package com.tunein.bryantyoung.tunein;

import android.app.Activity;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
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;
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 com.tunein.bryantyoung.tunein.MusicService.MusicBinder;
import android.widget.MediaController.MediaPlayerControl;

public class MainActivity extends Activity 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 methods
     */
    @Override
    public void start() {
        musicSrv.go();
    }

    @Override
    public void pause() {
        playbackPaused=true;
        musicSrv.pausePlayer();
    }

    @Override
    public int getDuration() {
        if(musicSrv!=null &amp;&amp; musicBound &amp;&amp; musicSrv.isPng())
            return musicSrv.getDur();
        else return 0;
    }

    @Override
    public int getCurrentPosition() {
        if(musicSrv!=null &amp;&amp; musicBound &amp;&amp; musicSrv.isPng())
        return musicSrv.getPosn();
        else return 0;
    }

    @Override
    public void seekTo(int pos) {
        musicSrv.seek(pos);
    }

    @Override
    public boolean isPlaying() {
        if(musicSrv!=null &amp;&amp; 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;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        songView = (ListView)findViewById(R.id.song_list);//retrieves the list view using ID
        songList = new ArrayList<Song>();//instantiates list view
        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();
    }

    @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 boolean onOptionsItemSelected(MenuItem item) {
        //menu item selected
        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();
    }

    @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();
    }


    /**
     * Helpers
     */

    //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;
        }
    };

    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);

        //Iterate over the results
        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){
        musicSrv.setSong(Integer.parseInt(view.getTag().toString()));
        musicSrv.playSong();
        if(playbackPaused){
            setController();
            playbackPaused=false;
        }
        controller.show(0);
    }

    private void setController(){
        //set the controller up
        controller = new MusicController(this);

        //Click listeners for next and Prev
        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);
    }

    //play next
    private void playNext(){
        musicSrv.playNext();
        if(playbackPaused){
            setController();
            playbackPaused=false;
        }
        controller.show(0);
    }

    //play prev
    private void playPrev(){
        musicSrv.playPrev();
        if(playbackPaused){
            setController();
            playbackPaused=false;
        }
        controller.show(0);
    }

}

“守则”是音乐播放器应用程序的主要活动，我遇到问题的行是假设是条件语句但我自己不确定它是如何工作的我之前没有做过类似的陈述。 / p>

Answer 1

&是符号&的网络编码。

如果您将所有&更改为&，您的代码就可以使用，因此代码如下：

musicSrv!=null && musicBound

而不是：

musicSrv!=null &amp;&amp; musicBound

希望它有所帮助！

＆＃39; Unexpexted Symbol＆amp;＆＃39;和＆＃39;无法解析符号放大器＆＃39;

1 个答案: