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

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];

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];

Listing 2-3  Creating an application music player
MPMusicPlayerController* appMusicPlayer =
    [MPMusicPlayerController applicationMusicPlayer];
 
[appMusicPlayer setShuffleMode: MPMusicShuffleModeOff];
[appMusicPlayer setRepeatMode: MPMusicRepeatModeNone];

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
}

• – setQueueWithQuery:
• – setQueueWithItemCollection:

3.MPMediaPickerController的使用

- (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];
}

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

#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];
}

4.MPMediaItem

用此方法来获取item的metadata

- (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

- (id) valueForProperty: (NSString *) property

创建

• + collectionWithItems:
• – initWithItems:

属性

•   items  property
•   representativeItem  property
•   count  property
•   mediaTypes  property

6.MPMediaPlaylist

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

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

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

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];

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

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];
}

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

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"];
}