音樂播放

1.訪問音樂庫的兩種方法，如下圖

（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，當程序退出後停止播放；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

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

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];

２.創建並配置一個Music　Player

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
}

３.設置播放隊列

• – setQueueWithQuery:
• – setQueueWithItemCollection:

４.控制播放

3.MPMediaPickerController的使用

<span style="font-size:18px;">- (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

<span style="font-size:18px;">#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

用此方法來獲取item的metadata

- (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

- (id) valueForProperty: (NSString *) property

創建

• + collectionWithItems:
• – initWithItems:

屬性

•   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

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

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

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的一些簡便構造方法

專輯封面的使用

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"];
}