如何从iOS上的播放列表中播放歌曲(仅限歌曲)？

Question

我正在尝试播放iPod播放列表中的歌曲.至于播放列表也可能有视频,我想只播放其中的歌曲.

    MPMusicPlayerController *mp = [MPMusicPlayerController applicationMusicPlayer];

    MPMediaQuery *query = [MPMediaQuery songsQuery];

    query.groupingType = MPMediaGroupingPlaylist;

    NSArray *playlists = [query collections];

    BOOL found = NO;

    for(MPMediaPlaylist *playlist in playlists)
    {
        NSString *name = [playlist valueForProperty:MPMediaPlaylistPropertyName];
        if([name caseInsensitiveCompare:@"MyPlaylist"] == NSOrderedSame && [playlist count] > 0)
        {
            MPMediaItemCollection *collection = [MPMediaItemCollection collectionWithItems:playlist.items];
            [mp setQueueWithItemCollection:collection];
            found = YES;
            NSLog(@"items count %d", [playlist count]);
            for (MPMediaItem *item in [collection items]){
                NSLog(@"%@", [item valueForKey:MPMediaItemPropertyMediaType]);
            }
            break;
        }
    }

在我加载1首歌曲和2个视频的播放列表后,输出为:

items count 3
256
256
1

我不明白为什么我也会收到视频,如果查询是为了检索歌曲,而媒体项目的媒体类型是MPMediaTypeMovie(256或1 << 8).

有什么建议吗？

Answer 1

一种可能的解决方法是使用谓词创建自定义查询.这可以通过使用MPMediaQuery items数组而不是collections数组来实现.该collections数组是一个MPMediaItemCollections 数组.该items数组是一个MPMediaItems 数组,因此您可以通过过滤查询MPMediaItemPropertyMediaType.MPMediaItemPropertyMediaType仅适用于a MPMediaItem而非a MPMediaItemCollection.

使用一组基于播放列表标题和媒体类型的谓词初始化查询.这将选择您的播放列表并过滤掉查询中的所有视频:

NSString *playlistName = @"MyPlaylist";
MPMediaPropertyPredicate *playlistPredicate = [MPMediaPropertyPredicate predicateWithValue:playlistName
                                                                               forProperty:MPMediaPlaylistPropertyName];

NSNumber *mediaTypeNumber = [NSNumber numberWithInteger:MPMediaTypeMusic]; // == 1
MPMediaPropertyPredicate *mediaTypePredicate = [MPMediaPropertyPredicate predicateWithValue:mediaTypeNumber
                                                                                forProperty:MPMediaItemPropertyMediaType];

NSSet *predicateSet = [NSSet setWithObjects:playlistPredicate, mediaTypePredicate, nil];
MPMediaQuery *mediaTypeQuery = [[MPMediaQuery alloc] initWithFilterPredicates:predicateSet];
[mediaTypeQuery setGroupingType:MPMediaGroupingPlaylist];

MPMediaPropertyPredicate如果从MPMediaQuery collections阵列返回数组,则不会过滤这些s .您应该在日志语句中看到1以外的媒体项类型:

NSArray *playlistCollections = [mediaTypeQuery collections];

[playlistCollections enumerateObjectsUsingBlock:^(MPMediaPlaylist *playlist, NSUInteger idx, BOOL *stop) {
    NSLog (@"Playlist title: %@", [playlist valueForProperty:MPMediaPlaylistPropertyName]);
    NSArray *songs = [playlist items];
    [songs enumerateObjectsUsingBlock:^(MPMediaItem *song, NSUInteger idx, BOOL *stop) {
        NSString *songTitle = [song valueForProperty:MPMediaItemPropertyTitle];
        NSInteger mediaValue = [[song valueForProperty:MPMediaItemPropertyMediaType] integerValue];
        if (mediaValue != 1) 
            NSLog(@"title: %@ - media type value: %d", songTitle, mediaValue);
    }]; // Should return other media types here.
}];  

该MPMediaPropertyPredicate如果从回报您的数组S将筛选MPMediaQuery items:

NSArray *playlistItems = [mediaTypeQuery items];

[playlistItems enumerateObjectsUsingBlock:^(MPMediaItem *song, NSUInteger idx, BOOL *stop) {
    NSString *songTitle = [song valueForProperty: MPMediaItemPropertyTitle];
    NSInteger mediaValue = [[song valueForProperty:MPMediaItemPropertyMediaType] integerValue];
    if (mediaValue != 1) 
        NSLog(@"title: %@ - media type value: %d", songTitle, mediaValue);
}]; // Should return nothing here.

您还可以通过以下方式仅使用mediaTypePredicate将媒体类型过滤器应用于整个库songsQuery:

MPMediaQuery *query = [MPMediaQuery songsQuery];
[query setGroupingType:MPMediaGroupingPlaylist];
[mediaTypeQuery addFilterPredicate:mediaTypePredicate];
NSArray *playlists = [query items];