访问音乐库

#import <UIKit/UIKit.h>
#import <MediaPlayer/MediaPlayer.h>

@interface ViewController : UIViewController<MPMediaPickerControllerDelegate, UITextFieldDelegate>

@property (weak, nonatomic) IBOutlet UILabel *infoLabel;
@property (weak, nonatomic) IBOutlet UISlider *volumeSlider;
@property (weak, nonatomic) IBOutlet UIButton *playButton;
@property (weak, nonatomic) IBOutlet UITextField *artistTextField;
@property (strong, nonatomic) MPMediaItemCollection *myCollection;
@property (strong, nonatomic) MPMusicPlayerController *player;

- (IBAction)addItems:(id)sender;
- (IBAction)prevTapped:(id)sender;
- (IBAction)playTapped:(id)sender;
- (IBAction)nextTapped:(id)sender;
- (IBAction)updateVolume:(id)sender;
- (IBAction)queueMusicByArtist:(id)sender;

@end

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController
@synthesize infoLabel;
@synthesize volumeSlider;
@synthesize playButton;
@synthesize artistTextField;

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    self.infoLabel.text = @"...";
    
    self.player = [MPMusicPlayerController applicationMusicPlayer];
    
    [self setNotifications];
    
    [self.player beginGeneratingPlaybackNotifications];
    
    [self.player setShuffleMode:MPMusicShuffleModeOff];
    self.player.repeatMode = MPMusicRepeatModeNone;
    
    self.volumeSlider.value = self.player.volume;
    
    self.artistTextField.delegate = self;
    self.artistTextField.enablesReturnKeyAutomatically = YES;
}

-(void)setNotifications
{
    NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];
    
    [notificationCenter
     addObserver: self
     selector:    @selector(handleNowPlayingItemChanged:)
     name:        MPMusicPlayerControllerNowPlayingItemDidChangeNotification
     object:      self.player];
    
    [notificationCenter
     addObserver: self
     selector:    @selector(handlePlaybackStateChanged:)
     name:        MPMusicPlayerControllerPlaybackStateDidChangeNotification
     object:      self.player];
    
    [notificationCenter
     addObserver: self
     selector:    @selector(handleVolumeChangedFromHardware:)
     name:        @"AVSystemController_SystemVolumeDidChangeNotification"
     object:      nil];
}

-(void)handleVolumeChangedFromHardware:(id)sender
{
    [self.volumeSlider setValue:self.player.volume animated:YES];
}

- (void) handlePlaybackStateChanged: (id) notification
{
    MPMusicPlaybackState playbackState = [self.player playbackState];
    
    if (playbackState == MPMusicPlaybackStateStopped)
    {
        [self.playButton setTitle:@"Play" forState:UIControlStateNormal];
    }
    else if (playbackState == MPMusicPlaybackStatePaused)
    {
        [self.playButton setTitle:@"Play" forState:UIControlStateNormal];
    }
    else if (playbackState == MPMusicPlaybackStatePlaying)
    {
        [self.playButton setTitle:@"Pause" forState:UIControlStateNormal];
    }
}

- (void) handleNowPlayingItemChanged: (id) notification
{
    MPMediaItem *currentItemPlaying = [self.player nowPlayingItem];
    if (currentItemPlaying)
    {
        NSString *info = [NSString stringWithFormat:@"%@ - %@", [currentItemPlaying valueForProperty:MPMediaItemPropertyTitle], [currentItemPlaying valueForProperty:MPMediaItemPropertyArtist]];
        self.infoLabel.text = info;
    }
    else
    {
        self.infoLabel.text = @"...";
    }
}

-(void)mediaPickerDidCancel:(MPMediaPickerController *)mediaPicker
{
    [self dismissViewControllerAnimated:YES completion:NULL];
}

-(void)mediaPicker:(MPMediaPickerController *)mediaPicker didPickMediaItems:(MPMediaItemCollection *)mediaItemCollection
{
    [self updateQueueWithMediaItemCollection:mediaItemCollection];
    [self dismissViewControllerAnimated:YES completion:NULL];
}

-(void)updateQueueWithMediaItemCollection:(MPMediaItemCollection *)collection
{
    if (collection)
    {
        if (self.myCollection == nil)
        {
            self.myCollection = collection;
            [self.player setQueueWithItemCollection: self.myCollection];
            [self.player play];
        }
        else
        {
            BOOL wasPlaying = NO;
            if (self.player.playbackState == MPMusicPlaybackStatePlaying)
            {
                wasPlaying = YES;
            }
            
            MPMediaItem *nowPlayingItem        = self.player.nowPlayingItem;
            NSTimeInterval currentPlaybackTime = self.player.currentPlaybackTime;
            
            NSMutableArray *combinedMediaItems =
            [[self.myCollection items] mutableCopy];
            NSArray *newMediaItems = [collection items];
            [combinedMediaItems addObjectsFromArray: newMediaItems];
            
            self.myCollection = [MPMediaItemCollection collectionWithItems:combinedMediaItems];
            
            [self.player setQueueWithItemCollection:self.myCollection];
            
            self.player.nowPlayingItem      = nowPlayingItem;
            self.player.currentPlaybackTime = currentPlaybackTime;
            
            if (wasPlaying)
            {
                [self.player play];
            }
        }
    }
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)addItems:(id)sender
{
    MPMediaPickerController *picker = [[MPMediaPickerController alloc] initWithMediaTypes:MPMediaTypeMusic];
    picker.delegate = self;
    picker.allowsPickingMultipleItems = YES;
    picker.prompt =
    NSLocalizedString (@"Add songs to play",
                       "Prompt in media item picker");
    [self presentViewController:picker animated:YES completion:NULL];
}

- (IBAction)prevTapped:(id)sender
{
    if ([self.player currentPlaybackTime] > 5.0)
    {
        [self.player skipToBeginning];
    }
    else
    {
        [self.player skipToPreviousItem];
    }
}

- (IBAction)playTapped:(id)sender
{
    if ((self.myCollection != nil) && (self.player.playbackState != MPMusicPlaybackStatePlaying))
    {
        [self.player play];
        [self.playButton setTitle:@"Pause" forState:UIControlStateNormal];
    }
    else if (self.player.playbackState == MPMusicPlaybackStatePlaying)
    {
        [self.player pause];
        [self.playButton setTitle:@"Play" forState:UIControlStateNormal];
    }
}

- (IBAction)nextTapped:(id)sender
{
    [self.player skipToNextItem];
}

- (IBAction)updateVolume:(id)sender
{
    self.player.volume = self.volumeSlider.value;
}

- (IBAction)queueMusicByArtist:(id)sender
{
    NSString *artist = self.artistTextField.text;
    if (artist != nil && artist != @"")
    {
        MPMediaPropertyPredicate *artistPredicate = [MPMediaPropertyPredicate predicateWithValue:artist forProperty:MPMediaItemPropertyArtist comparisonType:MPMediaPredicateComparisonContains];
        MPMediaQuery *query = [[MPMediaQuery alloc] init];
        [query addFilterPredicate:artistPredicate];
        
        NSArray *result = [query items];
        if ([result count] > 0)
        {
            [self updateQueueWithMediaItemCollection:[MPMediaItemCollection collectionWithItems:result]];
        }
        else
            self.infoLabel.text = @"Artist Not Found.";
    }
}

-(BOOL)textFieldShouldReturn:(UITextField *)textField
{
    [textField resignFirstResponder];
    [self queueMusicByArtist:self];
    return NO;
}