多媒体开发：音频录制、播放与音乐库访问

# 多媒体开发：音频录制、播放与音乐库访问 ## 1. 音频录制与播放基础 在音频开发中，当播放器完成播放后，需要重置按钮标题。以下是相应的委托方法： ```objc -(void)audioPlayerDidFinishPlaying:(AVAudioPlayer *)player successfully:(BOOL)flag { [self.playButton setTitle:@"Play" forState:UIControlStateNormal]; } ``` 同时，还需要处理中断情况。当音频播放或录制中断结束时，如果满足恢复条件，应继续播放或录制： ```objc - (void)audioPlayerEndInterruption:(AVAudioPlayer *)player withOptions:(NSUInteger)flags { if (flags == AVAudioSessionInterruptionOptionShouldResume) { [player play]; } } - (void)audioRecorderEndInterruption:(AVAudioRecorder *)recorder withOptions:(NSUInteger)flags { if (flags == AVAudioSessionInterruptionOptionShouldResume) { [recorder record]; } } ``` 通过这些代码，我们可以实现一个功能完整的音频录制和播放应用。 ## 2. 访问音乐库 ### 2.1 项目准备 要访问用户的音乐库，需要创建一个新的项目，并将其与 Media Player 框架链接。同时，在视图控制器的头文件中添加导入语句： ```objc #import <MediaPlayer/MediaPlayer.h> ``` ### 2.2 基本音乐播放器设置 创建基本音乐播放器的用户界面，需要设置以下控件的出口和动作： - **出口**： - `infoLabel`：用于显示信息。 - `volumeSlider`：用于控制音量。 - `playButton`：播放按钮。 - **动作**： - `addItems`：添加音乐到队列。 - `prevTapped`、`playTapped`、`nextTapped`：分别对应上一曲、播放/暂停、下一曲按钮。 - `updateVolume`：音量滑块值改变时更新音量。 在头文件中定义以下属性： ```objc @interface ViewController : UIViewController<MPMediaPickerControllerDelegate> @property (weak, nonatomic) IBOutlet UILabel *infoLabel; @property (weak, nonatomic) IBOutlet UISlider *volumeSlider; @property (weak, nonatomic) IBOutlet UIButton *playButton; @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; @end ``` 在 `viewDidLoad` 方法中进行初始化： ```objc - (void)viewDidLoad { [super viewDidLoad]; 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; } ``` 需要注意的是，`MPMusicPlayerController` 有两种获取实例的方法： - `applicationMusicPlayer`：应用特定的音乐播放器，应用进入后台后无法播放。 - `iPodMusicPlayer`：可在后台持续播放，但需要处理可能已存在的播放项。 ### 2.3 处理通知 为了及时响应播放状态和当前播放歌曲的变化，需要注册通知。以下是 `setNotifications` 方法的实现： ```objc -(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]; } ``` 同时，实现相应的通知处理方法： ```objc -(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 = @". . ."; } } ``` ### 2.4 选择媒体播放 使用 `MPMediaPickerController` 类可以方便地让用户选择音乐。以下是 `addItems` 方法的实现： ```objc - (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]; } ``` 同时，实现 `MPMediaPickerControllerDelegate` 协议的两个委托方法： ```objc -(void)mediaPickerDidCancel:(MPMediaPickerController *)mediaPicker { [self dismissViewControllerAnimated:YES completion:NULL]; } -(void)mediaPicker:(MPMediaPickerController *)mediaPicker didPickMediaItems:(MPMediaItemCollection *)mediaItemCollection { [self updateQueueWithMediaItemCollection:mediaItemCollection]; [self dismissViewControllerAnimated:YES completion:NULL]; } ``` `updateQueueWithMediaItemCollection` 方法用于更新媒体播放器的队列： ```objc -(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] ```