訪問iPod Library及MPMusicPlayerController

1.訪問音樂庫的兩種方法，

（只能訪問音頻文件，如music，podcast，audiobook等）

2.MPMusicPlayerController的使用

有兩種播放器可以選擇，一種是application　music　player，另外一種是iPod　music　player。

第一種播放器是一種內部播放器，當程序對出後停止播放；而第二種播放器則與iPod播放器內的信息相關，退出之後不會停止播放。獲取方式如下：

• + applicationMusicPlayer
• + iPodMusicPlayer

播放之前需要設置播放器的播放隊列

• – setQueueWithQuery:
• – setQueueWithItemCollection:

管理播放模式和播放狀態的一些屬性

•   currentPlaybackTime  property
•   nowPlayingItem  property
•   playbackState  property
•   repeatMode  property
•   shuffleMode  property
•   volume  property

播放狀態　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

播放狀態發生變化時可以發送通知

• – beginGeneratingPlaybackNotifications
• – endGeneratingPlaybackNotifications

MPMusicPlayerControllerPlaybackStateDidChangeNotification

可以通過該通知來改變播放按鈕的樣式

MPMusicPlayerControllerNowPlayingItemDidChangeNotification

MPMusicPlayerControllerVolumeDidChangeNotification

具體步驟

１.註冊和開始發送通知

 

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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.創建並配置一個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.設置播放隊列

 

 

• – 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]; }

主要是設置代理和選擇多媒體類型，然後通過代理方法來獲取選中的歌曲

 

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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

用此方法來獲取item的metadata

1	- (id) valueForProperty: (NSString *) property

NSString *const MPMediaItemPropertyTitle;                   

NSString *const MPMediaItemPropertyAlbumTitle;              

NSString *const MPMediaItemPropertyArtist;                 

 

 

5.MPMediaItemCollection

collection是一組有序的item集合，可用同樣的方法來獲取collection的metadata

1	- (id) valueForProperty: (NSString *) property

創建

• + collectionWithItems:
• – initWithItems:

屬性

•   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

需要設置兩個屬性: filter  and  grouping type

filter描述查詢內容，grouping type 描述返回內容的排列方式

查詢可以獲取items，也可以獲取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.

獲取全部歌曲

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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); }

獲取名爲“Happy the Clown”的藝術家的歌曲

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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];

多個查找條件，查找名爲"Sad the Joker"的藝術家的"Stair Tumbling"專輯

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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的一些簡便構造方法

專輯封面的使用

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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"]; }