February 2017
Beginner to intermediate
472 pages
9h 53m
Chinese
Content preview from Swift学习手册
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代码质量和应用分发
｜
449
创建
DocumentViewController
时会立即创建
AVSpeechSynthesizer
。然而，严格来
说无需立即创建
AVSpeechSynthesizer
，可以等到用户想朗读文本时再创建。
这个问题最好的解决方法是把
AVSpeechSynthesizer
存储为惰性存储属性（
lazy
stored property
）。惰性属性的作用与其他属性类似，只不过它不会立即初始化，而
是等到首次访问时才初始化。如果把
speechSynthesizer
改成惰性属性，那么加载
DocumentViewController
的时间就会减少。
5.
打开
DocumentViewController.swift
，把下面这行代码：
let speechSynthesizer = AVSpeechSynthesizer()
改成：
lazy var speechSynthesizer = AVSpeechSynthesizer()
搞定！再次执行前述步骤：重新启动应用，转到
Instruments
中，然后打开一个文档。加
载文档的时间应该会减少。
评估应用所做的事情，找出需要修改的地方，然后优化。这个过程可以做很多次，而且
以不同的方式做。这一节只说明了如何减少
CPU
时间。不过，你可以使用相同的原理
减少内存消耗量、数据读写量和网络数据传输量。
17.3
测试
简单的应用易于测试，但是复杂的应用很难正确测试。人们喜欢先添加一些代码，然后
检查是否可行。可是，添加的代码量越多，某部分代码破坏其他部分的几率就越大。为 ...
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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.