January 2020
Intermediate to advanced
356 pages
6h 4m
Chinese
Content preview from Swift游戏开发经典实例
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声音
｜
133
讨论
AVAudioPlayer
允许反复播放音频，但却不能改变它所播放的声音文件。如果想重
用一个
AVAudioPlayer
，我们只能播放相同的文件，如果要播放不同的文件，我们
必须创建新的
AVAudioPlayer
。
也就是说，
AVAudioPlayerPool
类必须知道你要播放哪个文件。
AVAudioPlayerPool
类为我们做了这些事情：
1.
用一个数组保存了所有的
AVAudioPlayer
对象。
2.
当你向它索取一个
AVAudioPlayer
对象时，它会去数组中查找空闲的、并
且
URL
为指定的
URL
的
AVAudioPlayer
对象，如果找到，则返回这个
AVAudioPlayer
对象。
3.
如果没有找到符合条件的
AVAudoPlayer
对象（要么是相同
URL
的
AVAudioPlayer
正在播放声音，要么是根本就没有包含这个
URL
的
AVAudioPlayer
），它会创建一个新的
AVAudioPlayer
对象，用指定
URL
进
行初始化，然后将对象放入到
AVAudioPlayer
数组中。这样，当这个新的
AVAudioPlayer
对象播放完毕后，我们又可以重用它了。
4.4
两个声音间的淡入淡出
问题
如何在多个声音间进行平滑过渡？即一个淡出，另一个淡入。
解决方案
下面的方法实现了一个声音淡入淡出的效果（指定开始音量、结束音量和过渡时间）：
func fade(player: AVAudioPlayer,
fromVolume startVolume : Float, ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.