访问iPod Library及MPMusicPlayerController的一些总结

 

 

1.访问音乐库的两种方法，

（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

 

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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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- (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

 

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#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

1	- (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

1	- (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"]; }