ios获取音乐库信息（转）

1.访问音乐库的两种方法，如下图
（只能访问音频文件，如music，podcast，audiobook等）
2.MPMusicPlayerController的使用
有两种播放器可以选择，一种是application　music　player，另外一种是iPod　music　player。
第一种播放器是一种内部播放器，当程序对出后停止播放；而第二种播放器则与iPod播放器内的信息相关，退出之后不会停止播放。获取方式如下：

+ applicationMusicPlayer
+ iPodMusicPlayer

播放之前需要设置播放器的播放队列
– setQueueWithQuery:
– setQueueWithItemCollection:
管理播放模式和播放状态的一些属性
  currentPlaybackTime  property
  nowPlayingItem  property
  playbackState  property
  repeatMode  property
  shuffleMode  property
  volume  property
播放状态　MPMusicPlaybackState
enum {
   MPMusicPlaybackStateStopped,
   MPMusicPlaybackStatePlaying,
   MPMusicPlaybackStatePaused,
   MPMusicPlaybackStateInterrupted,
   MPMusicPlaybackStateSeekingForward,
   MPMusicPlaybackStateSeekingBackward
};
typedef NSInteger MPMusicPlaybackState;

播放控制方法
– play
– pause
– stop
– beginSeekingForward
– beginSeekingBackward
– endSeeking
– skipToNextItem
– skipToBeginning
– skipToPreviousItem
播放状态发生变化时可以发送通知
– beginGeneratingPlaybackNotifications
– endGeneratingPlaybackNotifications
MPMusicPlayerControllerPlaybackStateDidChangeNotification
可以通过该通知来改变播放按钮的样式
MPMusicPlayerControllerNowPlayingItemDidChangeNotification
MPMusicPlayerControllerVolumeDidChangeNotification

具体步骤
１.注册和开始发送通知

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Listing 2-1  Registering for and activating music player notifications
NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];  

[notificationCenter
    addObserver: self
    selector:    @selector (handle_NowPlayingItemChanged:)
    name:        MPMusicPlayerControllerNowPlayingItemDidChangeNotification
    object:      musicPlayer];  

[notificationCenter
    addObserver: self
    selector:    @selector (handle_PlaybackStateChanged:)
    name:        MPMusicPlayerControllerPlaybackStateDidChangeNotification
    object:      musicPlayer];  

[musicPlayer beginGeneratingPlaybackNotifications];  

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Listing 2-2  Unregistering and deactivating music player notifications
[[NSNotificationCenter defaultCenter]
    removeObserver: self
    name:           MPMusicPlayerControllerNowPlayingItemDidChangeNotification
    object:         musicPlayer];  

[[NSNotificationCenter defaultCenter]
    removeObserver: self
    name:           MPMusicPlayerControllerPlaybackStateDidChangeNotification
    object:         musicPlayer];  

[musicPlayer endGeneratingPlaybackNotifications];  

２.创建并配置一个Music　Player

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Listing 2-3  Creating an application music player
MPMusicPlayerController* appMusicPlayer =
    [MPMusicPlayerController applicationMusicPlayer];  

[appMusicPlayer setShuffleMode: MPMusicShuffleModeOff];
[appMusicPlayer setRepeatMode: MPMusicRepeatModeNone];  

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Listing 2-4  Creating an iPod music player
MPMusicPlayerController* iPodMusicPlayer =
    [MPMusicPlayerController iPodMusicPlayer];  

if ([iPodMusicPlayer nowPlayingItem]) {
    // Update the UI (artwork, song name, volume indicator, etc.)
    //        to reflect the iPod state
}  

３.设置播放队列

– setQueueWithQuery:
– setQueueWithItemCollection:
４.控制播放

3.MPMediaPickerController的使用

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<span >- (IBAction)addSongsToMusicPlayer:(id)sender
{
    MPMediaPickerController *mpController = [[MPMediaPickerController alloc] initWithMediaTypes:MPMediaTypeMusic];
    mpController.delegate = self;
    mpController.prompt = @"Add songs to play";
    mpController.allowsPickingMultipleItems = YES;  

    [self presentModalViewController:mpController animated:YES];
    [mpController release];
}
</span>  

主要是设置代理和选择多媒体类型，然后通过代理方法来获取选中的歌曲

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<span >#pragma mark - Media Picker Delegate Methods  

- (void)mediaPicker:(MPMediaPickerController *)mediaPicker didPickMediaItems:(MPMediaItemCollection *)mediaItemCollection
{
    [self.musicPlayer setQueueWithItemCollection:mediaItemCollection];
    [self dismissModalViewControllerAnimated:YES];
}  

- (void)mediaPickerDidCancel:(MPMediaPickerController *)mediaPicker
{
    [self dismissModalViewControllerAnimated:YES];
}</span>  

4.MPMediaItem
用此方法来获取item的metadata
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- (id) valueForProperty: (NSString *) property  

NSString *const MPMediaItemPropertyTitle;
NSString *const MPMediaItemPropertyAlbumTitle;
NSString *const MPMediaItemPropertyArtist;                 

5.MPMediaItemCollection
collection是一组有序的item集合，可用同样的方法来获取collection的metadata
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- (id) valueForProperty: (NSString *) property  

创建
+ collectionWithItems:
– initWithItems:
属性
  items  property
  representativeItem  property
  count  property
  mediaTypes  property
6.MPMediaPlaylist

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MPMediaQuery *myPlaylistsQuery = [MPMediaQuery playlistsQuery];
NSArray *playlists = [myPlaylistsQuery collections];  

for (MPMediaPlaylist *playlist in playlists) {
    NSLog (@"%@", [playlist valueForProperty: MPMediaPlaylistPropertyName]);  

    NSArray *songs = [playlist items];
    for (MPMediaItem *song in songs) {
        NSString *songTitle =
            [song valueForProperty: MPMediaItemPropertyTitle];
        NSLog (@"\t\t%@", songTitle);
    }
}  

7.MPMediaQuery
需要设置两个属性: filter  and  grouping type
filter描述查询内容，grouping type 描述返回内容的排列方式

查询可以获取items，也可以获取collections
When you ask for items, the query returns a collection containing all the items that match the filter. The items are in “natural” order, meaning that they are ordered as iTunes shows them on the desktop.
When you ask for collections, the media query employs not only its filter but also its grouping type.

获取全部歌曲
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MPMediaQuery *everything = [[MPMediaQuery alloc] init];
NSLog(@"Logging items from a generic query...");
NSArray *itemsFromGenericQuery = [everything items];
for (MPMediaItem *song in itemsFromGenericQuery) {
    NSString *songTitle = [song valueForProperty: MPMediaItemPropertyTitle];
    NSLog (@"%@", songTitle);
}  

获取名为“Happy the Clown”的艺术家的歌曲
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MPMediaPropertyPredicate *artistNamePredicate =
    [MPMediaPropertyPredicate predicateWithValue: @"Happy the Clown"
                                     forProperty: MPMediaItemPropertyArtist];  

MPMediaQuery *myArtistQuery = [[MPMediaQuery alloc] init];
[myArtistQuery addFilterPredicate: artistNamePredicate];  

NSArray *itemsFromArtistQuery = [myArtistQuery items];  

多个查找条件，查找名为"Sad the Joker"的艺术家的"Stair Tumbling"专辑
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MPMediaPropertyPredicate *artistNamePredicate =
    [MPMediaPropertyPredicate predicateWithValue: @"Sad the Joker"
                                     forProperty: MPMediaItemPropertyArtist];  

MPMediaPropertyPredicate *albumNamePredicate =
    [MPMediaPropertyPredicate predicateWithValue: @"Stair Tumbling"
                                     forProperty: MPMediaItemPropertyAlbumTitle];  

MPMediaQuery *myComplexQuery = [[MPMediaQuery alloc] init];  

[myComplexQuery addFilterPredicate: artistNamePredicate];
[myComplexQuery addFilterPredicate: albumNamePredicate];  

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Listing 4-4  Applying multiple predicates when initializing a media query
NSSet *predicates =
    [NSSet setWithObjects: artistNamePredicate, albumNamePredicate, nil];  

MPMediaQuery *specificQuery =
    [[MPMediaQuery alloc] initWithFilterPredicates: predicates];  

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Listing 4-5  Testing if a property key can be used for a media property predicate
if ([MPMediaItem canFilterByProperty: MPMediaItemPropertyGenre]) {
    MPMediaPropertyPredicate *rockPredicate =
        [MPMediaPropertyPredicate predicateWithValue: @"Rock"
                                         forProperty: MPMediaItemPropertyGenre];
    [query addFilterPredicate: rockPredicate];
}  

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Listing 4-6  Using grouping type to specify media item collections
MPMediaQuery *query = [[MPMediaQuery alloc] init];  

[query addFilterPredicate: [MPMediaPropertyPredicate
                               predicateWithValue: @"Moribund the Squirrel"
                                      forProperty: MPMediaItemPropertyArtist]];
// Sets the grouping type for the media query
[query setGroupingType: MPMediaGroupingAlbum];  

NSArray *albums = [query collections];
for (MPMediaItemCollection *album in albums) {
    MPMediaItem *representativeItem = [album representativeItem];
    NSString *artistName =
        [representativeItem valueForProperty: MPMediaItemPropertyArtist];
    NSString *albumName =
        [representativeItem valueForProperty: MPMediaItemPropertyAlbumTitle];
    NSLog (@"%@ by %@", albumName, artistName);  

    NSArray *songs = [album items];
    for (MPMediaItem *song in songs) {
        NSString *songTitle =
            [song valueForProperty: MPMediaItemPropertyTitle];
        NSLog (@"\t\t%@", songTitle);
    }
}  

query的一些简便构造方法

专辑封面的使用

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Listing 4-7  Displaying album artwork for a media item
MPMediaItemArtwork *artwork =
    [mediaItem valueForProperty: MPMediaItemPropertyArtwork];
UIImage *artworkImage =
    [artwork imageWithSize: albumImageView.bounds.size];
if (artworkImage) {
    albumImageView.image = artworkImage;
} else {
    albumImageView.image = [UIImage imageNamed: @"noArtwork.png"];
}