通用音乐播放器说加载媒体时出错

Question

我正在使用 Google 提供的 Universal Music Player (UMP) 示例代码。

在这里，我想customize 按照我的requirement 做一件事，仍然UMP 在下面的过程中工作：

Screen 1: Genres (Songs by genre)

Screen 2: List of Genres

Screen 3: List of Songs (under particular Genre) 

现在，这是我的requirement：

我不需要Screen 1: Genres (Songs by genre)，我想直接从Screen 2 启动我的应用程序（即：List of Genres 屏幕）

为了达到我的目标，我对MusicService.java 类做了一个小改动。

我在下面的代码中有replaced：

/**
     * Actual implementation of onLoadChildren that assumes that MusicProvider is already
     * initialized.
     */
    private void loadChildrenImpl(final String parentMediaId,
                                  final Result<List<MediaBrowser.MediaItem>> result) {
        LogHelper.d(TAG, "OnLoadChildren: parentMediaId=", parentMediaId);

        List<MediaBrowser.MediaItem> mediaItems = new ArrayList<>();

        if (MEDIA_ID_ROOT.equals(parentMediaId)) {
            LogHelper.d(TAG, "OnLoadChildren.ROOT");
            mediaItems.add(new MediaBrowser.MediaItem(
                    new MediaDescription.Builder()
                        .setMediaId(MEDIA_ID_MUSICS_BY_GENRE)
                        .setTitle(getString(R.string.browse_genres))
                        .setIconUri(Uri.parse("android.resource://" +
                                "com.example.android.uamp/drawable/ic_by_genre"))
                        .setSubtitle(getString(R.string.browse_genre_subtitle))
                        .build(), MediaBrowser.MediaItem.FLAG_BROWSABLE
            ));

        } else if (MEDIA_ID_MUSICS_BY_GENRE.equals(parentMediaId)) {
            LogHelper.d(TAG, "OnLoadChildren.GENRES");
            for (String genre : mMusicProvider.getGenres()) {
                MediaBrowser.MediaItem item = new MediaBrowser.MediaItem(
                    new MediaDescription.Builder()
                        .setMediaId(createBrowseCategoryMediaID(MEDIA_ID_MUSICS_BY_GENRE, genre))
                        .setTitle(genre)
                        .setSubtitle(getString(R.string.browse_musics_by_genre_subtitle, genre))
                        .build(), MediaBrowser.MediaItem.FLAG_BROWSABLE
                );
                mediaItems.add(item);
            }

        } else if (parentMediaId.startsWith(MEDIA_ID_MUSICS_BY_GENRE)) {
            String genre = MediaIDHelper.getHierarchy(parentMediaId)[1];
            LogHelper.d(TAG, "OnLoadChildren.SONGS_BY_GENRE  genre=", genre);
            for (MediaMetadata track : mMusicProvider.getMusicsByGenre(genre)) {
                // Since mediaMetadata fields are immutable, we need to create a copy, so we
                // can set a hierarchy-aware mediaID. We will need to know the media hierarchy
                // when we get a onPlayFromMusicID call, so we can create the proper queue based
                // on where the music was selected from (by artist, by genre, random, etc)
                String hierarchyAwareMediaID = MediaIDHelper.createMediaID(
                        track.getDescription().getMediaId(), MEDIA_ID_MUSICS_BY_GENRE, genre);
                MediaMetadata trackCopy = new MediaMetadata.Builder(track)
                        .putString(MediaMetadata.METADATA_KEY_MEDIA_ID, hierarchyAwareMediaID)
                        .build();
                MediaBrowser.MediaItem bItem = new MediaBrowser.MediaItem(
                        trackCopy.getDescription(), MediaItem.FLAG_PLAYABLE);
                mediaItems.add(bItem);
            }
        } else {
            LogHelper.w(TAG, "Skipping unmatched parentMediaId: ", parentMediaId);
        }
        LogHelper.d(TAG, "OnLoadChildren sending ", mediaItems.size(),
                " results for ", parentMediaId);
        result.sendResult(mediaItems);
    }

使用following 代码：

/**
     * Actual implementation of onLoadChildren that assumes that MusicProvider is already
     * initialized.
     */
    private void loadChildrenImpl(final String parentMediaId,
                                  final Result<List<MediaBrowser.MediaItem>> result) {
        LogHelper.d(TAG, "OnLoadChildren: parentMediaId=", parentMediaId);

        List<MediaBrowser.MediaItem> mediaItems = new ArrayList<>();

        if (MEDIA_ID_MUSICS_BY_GENRE.equals(parentMediaId)) {
            LogHelper.d(TAG, "OnLoadChildren.GENRES");
            for (String genre : mMusicProvider.getGenres()) {
                MediaBrowser.MediaItem item = new MediaBrowser.MediaItem(
                    new MediaDescription.Builder()
                        .setMediaId(createBrowseCategoryMediaID(MEDIA_ID_MUSICS_BY_GENRE, genre))
                        .setTitle(genre)
                        .setSubtitle(getString(R.string.browse_musics_by_genre_subtitle, genre))
                        .build(), MediaBrowser.MediaItem.FLAG_BROWSABLE
                );
                mediaItems.add(item);
            }

        } else if (parentMediaId.startsWith(MEDIA_ID_MUSICS_BY_GENRE)) {
            String genre = MediaIDHelper.getHierarchy(parentMediaId)[1];
            LogHelper.d(TAG, "OnLoadChildren.SONGS_BY_GENRE  genre=", genre);
            for (MediaMetadata track : mMusicProvider.getMusicsByGenre(genre)) {
                // Since mediaMetadata fields are immutable, we need to create a copy, so we
                // can set a hierarchy-aware mediaID. We will need to know the media hierarchy
                // when we get a onPlayFromMusicID call, so we can create the proper queue based
                // on where the music was selected from (by artist, by genre, random, etc)
                String hierarchyAwareMediaID = MediaIDHelper.createMediaID(
                        track.getDescription().getMediaId(), MEDIA_ID_MUSICS_BY_GENRE, genre);
                MediaMetadata trackCopy = new MediaMetadata.Builder(track)
                        .putString(MediaMetadata.METADATA_KEY_MEDIA_ID, hierarchyAwareMediaID)
                        .build();
                MediaBrowser.MediaItem bItem = new MediaBrowser.MediaItem(
                        trackCopy.getDescription(), MediaItem.FLAG_PLAYABLE);
                mediaItems.add(bItem);
            }
        } else {
            LogHelper.w(TAG, "Skipping unmatched parentMediaId: ", parentMediaId);
        }
        LogHelper.d(TAG, "OnLoadChildren sending ", mediaItems.size(),
                " results for ", parentMediaId);
        result.sendResult(mediaItems);
    }

当我启动我的应用程序而不是 List of Genres 时，我得到了一个 message，上面写着："Error Loading Media"

所以what's wrong 在这里，Where I have to make change 在我的代码中？直接To get List of Genres

Answer 1

问题是 UMP 仍然使用parentMediaId == __ROOT__ 调用loadChildrenImpl()。

所以它在 if-else 语句中找不到合适的大小写，最终出现在

LogHelper.w(TAG, "Skipping unmatched parentMediaId: ", parentMediaId);

并返回 empty mediaItems（这会导致“Error Loading Media”错误）

修复是在MusicService 类中，在onGetRoot() 方法中替换

    return new BrowserRoot(MEDIA_ID_ROOT, null);

与

    return new BrowserRoot(MEDIA_ID_MUSICS_BY_GENRE, null);