Delete 6. 动画、音频与视频.md
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# 动画、音频与视频
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## 动画
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流畅的动画是 iOS 的灵魂所在。对于开发者而言，合理地使用动画，让用户体验得到提升是攻城狮们的必修课程。在前面的课程中我们 已经熟悉了对 Swift 的基础控件，接下来我们将把学习内容放到设计结构上。
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对于动画的应用一般在 View 控件上，动画的种类大体上分为仿射变换、旋转变换以及平移三 种，对于动画过程中的速度时间我们都可以进行设置，这三种变换是所有动画的基础，例如：我们可以通过平移来实现 app 的加载和退场，可以使用仿射变换实现音乐播放时封面的动画，从而让用户有真实感。此外，我们还可以通过旋转来使整个程序增添一份趣味。下面的代码罗列了一些基本的动画使用方法，你需要熟练掌握并且试着学会如何应用。在 playgrounds 中：
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```swift
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import UIKit
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import PlaygroundSupport
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//初始化 View
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let liveViewFrame = CGRect(x: 0, y: 0, width: 500, height: 500) let liveView = UIView(frame : liveViewFrame) liveView .
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backgroundColor = . white
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PlaygroundPage . current . liveView = liveView
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let smallFrame = CGRect(x: 0, y: 0, width: 100, height: 100)
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let square = UIView(frame: smallFrame)
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square.backgroundColor = .purple
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liveView.addSubview(square)
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//添加动画
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UIView.animate(withDuration: 2.0) {
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square . backgroundColor = . orange
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let scaleTransform = CGAffineTransform(scaleX : 2.0 , y: 2.0) //添加仿射变换
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let rotateTransform = CGAffineTransform(rotationAngle: .pi)//添加旋转变换
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let translateTransform = CGAffineTransform(translationX:200, y: 200) //添加移动变换
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let comboTransform = scaleTransform.concatenating(rotateTransform ).concatenating (translateTransform ) square .transform = comboTransform //将三种变换合成
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}
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```
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## 短效果音播放
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一个有趣的 app 离不开各种令人印象深刻的音效。在 Swift 中，我们通常使用 AudioToolbox 与 AVFoundation 来播放音频和视频。假设导入一个 30s 内的 wav 格式音频，并将其命名为 myVoice， 接下来，我们需要将该音频的所在路径设置为虚拟的 url 地址，并将音频播放的地址设置为该地址：
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```swift
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import UIKit
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import AudioToolbox
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class ViewController : UIViewController{
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override func viewDidLoad () {
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super.viewDidLoad ()
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var _soundId : SystemSoundID = 0
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let path = Bundle.main.path(forResource: ”myVioce”,ofType: ”wav”)
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let soundUrl = URL( fileURLWithPath : path ! )
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AudioServicesCreateSystemSoundID ( soundUrl as CFURL,&_soundId )
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AudioServicesAddSystemSoundCompletion(_soundId , nil , nil ,{(soundID , clientData ) −> Void in
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print(”音频播放后重复之前的播放”)
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AudioServicesPlaySystemSound ( soundID )
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}, nil)
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AudioServicesPlaySystemSound ( _soundId )
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}
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}
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```
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## 长音乐音乐播放
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在一款 app 中，仅仅有 30s 的效果音可能还不够，有时候我们需要导入长音乐。Swift 中内置了一款音乐播放器，对于基础开发者来说足够应用。该播放器的设置过程和短效果音的思路相同，我们也需要设置 url 路径来导入我们的本地音乐。请注意，Swift 内置的音频播放器中并没有暂停和继续播放的功能，我们需要手动设置一个 Button 来实现该效果：
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```swift
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import UIKit
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import AVFoundation
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class ViewController: UIViewController,AVAudioPlayerDelegate {
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var audioPlayer:AVAudioPlayer = AVAudioPlayer()
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//初始化音乐播放器为 AVAudioPlayer 格式
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override func viewDidLoad() {
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super.viewDidLoad()
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//令路径为项目文件下的音乐文件
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let path = Bundle.main.path(forResource: "兰亭序", ofType: "mp3") //将路径转化为 URL 路径
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let soundUrl = URL(fileURLWithPath: path!)
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do{
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try audioPlayer = AVAudioPlayer(contentsOf: soundUrl) audioPlayer.volume = 1.0
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//音频音量为 1.0
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audioPlayer.numberOfLoops = -1 //-1 为无限循环播放
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audioPlayer.delegate = self audioPlayer.play()
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} catch {
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print(error)
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}
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//定义一个暂停/恢复播放按钮
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let stopMusic = UIButton(frame: CGRect(x: 20, y: 80, width: 280, height: 44))
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stopMusic.backgroundColor = UIColor.blue
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stopMusic.setTitle("暂停/恢复音乐", for:UIControl.State.init(rawValue:0))
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//为该按钮添加点击事件
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stopMusic.addTarget(self, action: #selector(ViewController.pauseOrResumeMusic), for: .touchUpInside)
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self.view.addSubview(stopMusic)
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}
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//填写 objc 方法
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@objc func pauseOrResumeMusic(){
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if self.audioPlayer.isPlaying{
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//isPlaying 判断音乐是否在播放，若播放则暂停，反之亦然
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self.audioPlayer.pause()
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}else{
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self.audioPlayer.play()
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}
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}
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func audioPlayerBeginInterruption(_ player: AVAudioPlayer) {
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print("被打断")
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}
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func audioPlayerDidFinishPlaying(_ player: AVAudioPlayer, successfully flag: Bool) {
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print("播放完成")
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}
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}
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```
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附件中携带了一份我自己制作的兰亭序伴奏demo.mp3，你可以用这个音频文件进行功能实现尝试。
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## 视频播放
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实现了音频播放，该如何实现视频播放呢？Swift 中内置了视频播放的功能，总体上来说，本地视频播放的思路和音频一样，都需要我们设置视频的 url 地址，将本地视频导入其中。在此之前我们需要导入 AVFoundation 头文件，在 `viewDidLoad()`中：
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```swift
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let moviePath = Bundle.main.path(forResource: "movie", ofType: "mp4")
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let movieURL = URL(fileURLWithPath: moviePath!)
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let avPlayer = AVPlayer(url: movieURL as URL)
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let avPlayerLayer = AVPlayerLayer(player:avPlayer)
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avPlayerLayer.frame = self.view.bounds
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avPlayerLayer.videoGravity = AVLayerVideoGravity.resizeAspectFill self.view.layer.addSublayer(avPlayerLayer)
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avPlayer.play()
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```
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### 借助播放器
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在上面的代码中，我们实现了视频的播放，不过你可能发现在该 项目中我们无法进行暂停与快进，更不用提画中画和声音等功能，要想实现这些内容，我们需要借助 Swift 内置的播放器：
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```swift
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import UIKit
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import AVFoundation
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import AVKit
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class ViewController: UIViewController {
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override func viewDidLoad() {
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super.viewDidLoad()
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//设置视频路径，令 URL 为预设地址
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let moviePath = Bundle.main.path(forResource: "movie", ofType: "mp4")
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let movieURL = URL(fileURLWithPath: moviePath!)
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//设置播放器
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let avPlayer = AVPlayer(url:movieURL as URL)
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let playerVC = AVPlayerViewController()
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playerVC.player = avPlayer
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playerVC.videoGravity = AVLayerVideoGravity.resizeAspect
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/*.resizeAspectFill 等比缩小，填满整个范围
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.resizeAspect 等比播放，中间播放 */
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playerVC.allowsPictureInPicturePlayback = true
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playerVC.showsPlaybackControls = true playerVC.view.frame = self.view.bounds
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playerVC.player!.play()
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self.view.addSubview(playerVC.view)
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}
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}
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```
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