多媒体应用开发：音频播放与管理全解析

# 多媒体应用开发：音频播放与管理全解析 ## 1. 音频录制与播放基础 在音频应用开发中，实现音频的录制和播放是基础功能。当音频播放完成时，播放按钮的标题需要重置。以下是相应的代理方法： ```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，如电话或短信干扰。以下是处理音频播放和录制中断的方法： ```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]; } } ``` 通过这些方法，我们可以确保音频应用在遇到中断后能正确恢复播放或录制。 ## 2. 访问音乐库 除了处理项目中自带的音频文件，还可以通过访问用户的音乐库来获取更多音频资源。以下是实现这一功能的详细步骤： ### 2.1 创建新项目并引入框架 创建一个新项目，并将其与 Media Player 框架链接，同时在视图控制器中添加导入语句： ```objc #import <MediaPlayer/MediaPlayer.h> ``` ### 2.2 设置基本音乐播放器 设置视图以实现基本音乐播放器的功能，需要创建以下控件的出口和动作： | 控件类型 | 出口名称 | 动作名称 | 动作触发事件 | | ---- | ---- | ---- | ---- | | 标签 | infoLabel | 无 | 无 | | 滑块 | volumeSlider | updateVolume | Value Changed | | 按钮 | playButton | playTapped | 点击 | | 按钮 | 无 | addItems | Touch Up Inside | | 按钮 | 无 | prevTapped | 点击 | | 按钮 | 无 | nextTapped | 点击 | 同时，在头文件中定义两个属性： ```objc @property (strong, nonatomic) MPMusicPlayerController *player; @property (strong, nonatomic) MPMediaItemCollection *myCollection; ``` 并使视图控制器成为 `MPMediaPickerController` 的代理： ```objc @interface ViewController : UIViewController<MPMediaPickerControllerDelegate> ``` 头文件的完整代码如下： ```objc #import <UIKit/UIKit.h> #import <MediaPlayer/MediaPlayer.h> @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 ``` ### 2.3 初始化视图 在 `viewDidLoad` 方法中进行初始化设置： ```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` 有两个重要的类方法：`applicationMusicPlayer` 和 `iPodMusicPlayer`。`applicationMusicPlayer` 返回特定于应用的音乐播放器，应用进入后台后可能无法播放；`iPodMusicPlayer` 允许在后台持续播放，但需要处理可能已有的正在播放的项目。 ### 2.4 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： ```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]; } ``` 以下是处理不同通知的方法： ```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 = @". . ."; } } ``` ### 2.5 选择媒体播放 使用 `MPMediaPickerController` 类来添加音乐到播放列表： ```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，实现代理方法来处理媒体选择的取消和成功情况： ```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]; } ``` 以下是更新播放队列的方法： ```objc -(void)updateQu ```