java - 在Android的Media Player库中遇到问题

我正在尝试制作一个音乐应用，该应用从firebase加载Song Url，Song name和Artist name。我有两个活动，一个是ExtrasActivity .ExtrasActivity包含一个recyclerview，它在列表中加载歌曲，当我们单击item时，它会将songUrl，SongName和ArtistName发送到另一个名为StackActivity的活动。我在StackActivity中遇到问题，例如在播放歌曲时，如果我单击并播放另一首歌曲，则有时效果很好，但有时会一起播放两首歌曲。
我尝试了很多方法来解决此问题，但它们均无法正常工作，我认为StackActivity中存在问题。

这是我的StackActivity：

public class StackActivity extends AppCompatActivity implements MediaPlayer.OnPreparedListener {

    private MediaPlayer mediaPlayer;
    private Boolean isPlaying = false;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.stack_activity_name);

        SeekBar Song_playing_seekbar;

        TextView songInfoSong = findViewById(R.id.song_info_song);
        TextView songInfoArtist = findViewById(R.id.song_info_artist);

        songInfoSong.setText(getIntent().getStringExtra("Name"));
        songInfoArtist.setText(getIntent().getStringExtra("Artist"));

        mediaPlayer = new MediaPlayer();

        playSong();

    }

    private void playSong() {
        final FirebaseStorage storage = FirebaseStorage.getInstance();

        StorageReference storageReference = storage.getReferenceFromUrl(getIntent().getStringExtra("SongUrl"));

        storageReference.getDownloadUrl().addOnSuccessListener(new OnSuccessListener<Uri>() {
            @Override
            public void onSuccess(Uri uri) {

                try {


                    mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
                    final String url = uri.toString();
                    mediaPlayer.setDataSource(url);
                    mediaPlayer.setOnPreparedListener(StackActivity.this);
                    mediaPlayer.prepareAsync();


                } catch (Exception e) {
                    e.printStackTrace();

                }


            }
        }).addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Log.i("TAg", "aFailed");
            }
        });


    }

    @Override
    public void onPrepared(final MediaPlayer mediaPlayer) {

        CheckIfSongIsPlayingOrNot();

        if (isPlaying == false) {
            mediaPlayer.start();
        } else if (isPlaying == true) {
            mediaPlayer.stop();
        }

    }

    private void CheckIfSongIsPlayingOrNot() {
        if (mediaPlayer.isPlaying()) {
            isPlaying = true;
        } else if (!mediaPlayer.isPlaying()) {
            isPlaying = false;
        }
    }

因此，如果您发现任何问题，请帮助我进行改进。

最佳答案

这是因为每次启动MediaPlayer时都会重新创建StackActivity。我什至想知道为什么这种情况不会每次都发生。更确切地说，旧的MediaPlayer实例永远不会停止，甚至更重要的是释放。您应该仔细研究MediaPlayer docs以了解状态。

但是对于这种特定情况，我将尝试定义MediaPlayer Singleton。

public class MediaPlayerSingleton implements MediaPlayer.OnPreparedListener {

    private static MediaPlayerSingleton instance = null;
    private MediaPlayer mediaPlayer = null;

    private MediaPlayerSingleton() {
        mediaPlayer = new MediaPlayer();
        mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
        mediaPlayer.setOnPreparedListener(this);
    }

    public static MediaPlayerSingleton getInstance() {
        if (instance == null) {
            instance = new MediaPlayerSingleton();
        }
        return instance;
    }

    @Override
    public void onPrepared(MediaPlayer mediaPlayer) {
        resume();
    }

    /**
     * This will load the given URL into the media player.
     * @param url The URL string from the Firebase Uri.
     */
    public void play(String url) {
        try {
            mediaPlayer.reset()
            mediaPlayer.setDataSource(url);
            mediaPlayer.prepareAsync();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void pause() {
        mediaPlayer.pause();
    }

    public void resume() {
        mediaPlayer.start();
    }

    public void stop() {
        mediaPlayer.stop();
    }

    public void release() {
        mediaPlayer.release();
    }
}

然后，您可以在StackActivity中使用它。

public class StackActivity extends AppCompatActivity {

    // your onCreate() but leave out the MediaPlayer references

    private void playSong() {
        FirebaseStorage storage = FirebaseStorage.getInstance();
        StorageReference storageReference = storage.getReferenceFromUrl(getIntent().getStringExtra("SongUrl"));

        storageReference.getDownloadUrl().addOnSuccessListener(new OnSuccessListener<Uri>() {
            @Override
            public void onSuccess(Uri uri) {
                MediaPlayerSingleton.getInstance().play(uri.toString());
            }
        }).addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Log.i("TAg", "aFailed");
            }
        });
    }
}

但是请确保像这样在开始活动的release()（例如onDestroy()）中调用此单例的ExtrasActivity函数：

@Override
protected void onDestroy() {
    super.onDestroy();
    MediaPlayerSingleton.getInstance().release();
}

必须这样做以释放内存。

只是我提供的单例示例的旁注。这只是一个可以改进的简单示例，例如对MediaPlayer实例进行额外的null检查。但这应该给您一些基础。