如何使用 MediaPlayer Singleton

Question

我是 Android 开发新手，从一个简单的音板应用程序开始。我开始使用多个片段开发音板，直到我意识到我使用了多个 MediaPlayer 实例。这不好，因为我只想一次播放一种声音。

我意识到我必须使用 MediaPlayer Singleton 来解决我的问题。唯一的问题是我在网上找不到很多 MediaPlayer Singleton 的来源或示例。

这是我最初放入每个片段中的每个“onCreateView”中的内容：

public static class FragmentPage1 extends Fragment {

    int selectedSoundId;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_page1, container, false);


        final MediaPlayer player = new MediaPlayer();
        final Resources res = getResources();

        final int[] buttonIds = { R.id.btn1, R.id.btn2, R.id.btn3, R.id.btn4, R.id.btn5, R.id.btn6, R.id.btn7, R.id.btn8, R.id.btn9 };
        final int[] soundIds = { R.raw.sound01, R.raw.sound02, R.raw.sound03, R.raw.sound04, R.raw.sound05, R.raw.sound06, R.raw.sound07, R.raw.sound08, R.raw.sound09 };

        View.OnClickListener listener = new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                for (int i = 0; i < buttonIds.length; i++) {
                    if (v.getId() == buttonIds[i]) {
                        selectedSoundId = soundIds[i];
                        AssetFileDescriptor afd = res.openRawResourceFd(soundIds[i]);
                        player.reset();
                        try {
                            player.setDataSource(afd.getFileDescriptor(), afd.getStartOffset(), afd.getLength());
                        } catch (IllegalArgumentException e) {
                            e.printStackTrace();
                        } catch (IllegalStateException e) {
                            e.printStackTrace();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                        try {
                            player.prepare();
                        } catch (IllegalStateException e) {
                            e.printStackTrace();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                        player.start();
                        break;
                    }
                }
            }
        };

        for (int i = 0; i < buttonIds.length; i++) {
            ImageButton soundButton = (ImageButton) rootView.findViewById(buttonIds[i]);
            registerForContextMenu(soundButton);
            soundButton.setOnClickListener(listener);
        }
        return rootView;
    }
}

To my knowledge I'd probably put the onClickListener inside of each fragment and the MediaPlayer Singleton in a new Java class. I don't know what to do from there though.

How do I implement a MediaPlayer Singleton and how do I call it back in the fragment's "onCreateView" method?

Examples are highly appreciated and thanks!

Answer 1

看，Singleton 是一种设计模式，它是通过将默认构造函数设置为私有来实现的，那么您应该提供一个 get 方法，从中您可以恢复您的对象实例。看看下面的例子：

public class Foo {
    private MediaPlaye md;

    private Foo () {
        md = new MediaPlayer();
    }

    public MediaPlayer getMediaPlayer () {
        if (md == null) {
            new Foo();
        }
        return md;
    }
}

在您的情况下，最好的做法是创建一个 Service 类来封装所有 MediaPlayer 方法。这样做是因为，通常情况下，开发人员希望播放器继续播放，即使用户离开了它所绑定的 Activity。在每个要使用 MediaPlayer API 的片段中，您可以绑定 Service 并使用定义的接口。看看下面的类：

public class MusicPlayerService extends android.app.Service implements MediaPlayer.OnPreparedListener,
        MediaPlayer.OnErrorListener,
        MediaPlayer.OnCompletionListener,
        ObserverSubject {

    private static final int NOTIFY_ID = 1;
    private List<MusicPlayerObserver> mObservers;

    private MediaPlayer mMediaPlayer;
    private final IBinder playerBind = new MusicBinder();;

    private List<Track> mPlaylist;
    private Integer mPosition;

    private Boolean isRepeating;
    private Boolean isShuffling;
    private Boolean isPrepared;
    private Boolean isPaused;

    // Callback Methods______________________________________________
    @Override
    public void onCreate() {
        ...
    }

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

    @Override
    public IBinder onBind(Intent intent) {
        return playerBind;
    }

    @Override
    public boolean onUnbind(Intent intent) {
        mMediaPlayer.stop();
        mMediaPlayer.release();
        return false;
    }

    @Override
    public void onDestroy() {
        stopForeground(true);
    }

    @Override
    public boolean onError(MediaPlayer mp, int what, int extra) {
        mp.reset();
        return false;
    }


    // UTIL METHODS__________________________________________________
    private Long getCurrentTrackId() {
        return mPlaylist.get(mPosition).getTrackId();
    }

    private Long getCurrentAlbumId() {
        return mPlaylist.get(mPosition).getAlbumId();
    }



    // MEDIA PLAYER INTERFACE________________________________________

    public void play() {
        ...
    }

    public void pause() {
        ...
    }

    public void resume() {
        ...
    }

    public void next() {
        ...
    }

    public void previous() {
        ...
    }

    public void seekTo(int pos) {
        ...
    }

    // SERVICE INTERFACE PROVIDER_____________________________________
    /**
     * Interface through the component bound to this service can interact with it
     */
    public class MusicBinder extends Binder {
        public MusicPlayerService getService() {
            return MusicPlayerService.this;
        }
    }
}

我强烈建议您遵循这种创建 MusicPlayer 服务的策略。另外，我建议您查看另一个名为 Observer 的设计模式。通常，在音乐应用程序中，您希望根据 MP 状态更新多个 UI 元素。Observer 非常适合这种情况。

希望我有所帮助。