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将 定 位 new运算符用于对象。 • 使用指向对象的指针。 • 实现队列抽象数据类型(ADT)。 本章将介绍如何对类使用new和delete以及如何处理rt丨于使用动态内存而引起的一些微妙的问题。这 里涉及的主题好像不多，但它们将影响构造函数和析构函数的设计以及运算符的重载。 來看一个具休的例子~ O H •如何增加内存负载。假设要创建一个类，其一个成员表示某人的姓。敁简单的 方法是使用字符数组成员来保存姓，但这种方法有一些缺陷。开始也许会使用一个14个字符的数组，然iT;•发现数 组太小，更保险的方法是，使iH— 个40个字符的数组。然而，如果创建包含2000个这种对象的数组，就会由于 字符数组只有部分被使用而浪费人量的内存(在这种情况下，增加了计算机的内存负载)。但可以采取另一种方法。 通常，鉍好是在程序运行时(而+ 是编译时)确定诸如使用多少内存等问题。对于在对象中保存姓名 来说，通常的0 + 方法是，在类构造函数中使用new运算符在程序运行时分配所需的内存。为此，通常的 方法是使用string类，它将为您处理内存管理细节。但这样您就没有机会史深入地学习内存管理了，W 此 这里将直接对问题发起攻击。除非同时执行一系列额外步骤，如扩展类析构函数、使所有的构造函数与new 析构函数协调一致、编写额外的类方法来帮助正确完成初始化和赋值(当然，本章将介绍这些步骤>,否则， 在类构造函数中使用new将导致新问题。

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There are many reasons developers want to say “No” to Auto Layout. Maybe it’s too new, too strange, or requires a bit of work to update interfaces. But you should say “Yes.” Auto Layout revolutionizes view layout with something wonderful, fresh, and new. Apple’s layout features make your life easier and your interfaces more consistent, and they add resolution-independent placement for free. You get all this, regardless of device geometry, orientation, and window size. Auto Layout works by creating relationships between onscreen objects. It specifies the way the runtime system automatically arranges your views. The outcome is a set of robust rules that adapt to screen and window geometry. With Auto Layout, you describe constraints that specify how views relate to one another, and you set view properties that describe a view’s relationship to its content. With Auto Layout, you can make requests such as the following: ■ Match one view’s size to another view’s size so that they always remain the same width. ■ Center a view (or even a group of views) in a superview, no matter how much the superview reshapes. ■ Align the bottoms of several views while laying out a row of items. ■ Offset a pair of items by some constant distance (for example, adding a standard 8-point padding space between views).

Ever since I was 12 years old and wrote my first program in the BASIC programming language, programming has been a passion for me. Even as I became a professional programmer, programming remained more of a passion than a job, but in the years preceding the first release of Swift, that passion had waned. I was unsure why I was losing that passion. I attempted to recapture that passion with some of my side projects, but nothing really brought back the excitement that I used to have. Then Apple announced Swift in 2014. Swift is such an exciting and progressive language that it has brought a lot of that passion back and made programming fun again. Now that official versions of Swift are available for the Linux platform, and un-official versions for Windows and the ARM platform, learning and using Swift is becoming available to people outside the Apple ecosystem. This is really an exciting time to be learning the Swift language. In this chapter, you will learn: What is Swift? What are some of the features of Swift? What are Playgrounds? How to use Playgrounds? What the basic syntaxes of the Swift language are?

Swift 命令⾏⼯具 Swift 的 REPL (Read-Eval-Print Loop) 环境可以让我们使⽤ Swift 进⾏简单的交互式编程。也就是 说每输⼊⼀句语句就⽴即执⾏和输出。这在很多解释型的语⾔中是很常⻅的，⾮常适合⽤来对语 ⾔的特性进⾏学习。 要启动 REPL 环境，就要使⽤ Swift 的命令⾏⼯具，它是以 xcrun 命令的参数形式存在的。⾸先 我们需要确认使⽤的 Xcode 版本是否是 6.1 或者以上，如果不是的话，可以在 Xcode 设置⾥ Locations 中的 Command Line Tools ⼀项中进⾏选择。然后我们就可以在命令⾏中输⼊ xcrun swift 来启动 REPL 环境了。 要指出的是，REPL 环境只是表现得像是即时的解释执⾏，但是其实质还是每次输⼊代码后进⾏ 编译再运⾏。这就限制了我们不太可能在 REPL 环境中做很复杂的事情。 另⼀个⽤法是直接将⼀个 .swift ⽂件作为命令⾏⼯具的输⼊，这样⾥⾯的代码也会被⾃动地编译 和执⾏。我们甚⾄还可以在 .swift ⽂件最上⾯

本书假设你是iOS 开发人员，有长期开发原生iOS 应用的经验，并且希望能够从众人中脱 颖而出，跻身于顶尖开发人员之列。 参考以下统计数据。1 • 应用首次工作出错以后，79% 的用户只会再重试一两次。 • 当应用载入时间超过3 秒时，25% 的用户会放弃使用该应用。 • 31% 的用户会将糟糕的体验转告他人。 这些数据强调了性能对应用的重要性。应用能否被用户所认可不仅仅取决于其功能，还取 决于当与用户交互时，应用能否提供流畅的体验。 几乎完成任意特定任务的应用都能在App Store 中找到大量的替代品。但用户只会坚持使 用其中的某一款。被选中的这一款要么无可取代，要么极少出现故障且性能格外出众。 性能会受许多重要因素所影响，这些因素包括内存消耗、网络带宽效率以及用户界面的响 应速度。我们先概述不同类型的性能特征，然后再对它们进行测量。 1.1　定义性能 从技术视角严格来说，性能是非常模糊的术语。当一个人说“这是个高性能的应用”时， 其实我们无从判断他说的是什么。他是说应用消耗的内存少？应用节约了网络流量？还是 说应用使用起来非常流畅？总而言之，高性能有着多重的含义和丰富的解释方式。

通过定义一个私有访问权限的构造函数，避免被其他类new出来一个对象，而Emperor自 己则可以new一个对象出来，其他类对该类的访问都可以通过getInstance获得同一个对象。 皇帝有了，臣子要出场，其类如代码清单7-2所示。 代码清单7-2 臣子类 public class Minister { public static void main(String[] args) { for(int day=0;day<3;day++){ Emperor emperor=Emperor.getInstance(); emperor.say(); } //三天见的皇帝都是同一个人，荣幸吧！ } } 臣子参拜皇帝的运行结果如下所示

通过定义一个私有访问权限的构造函数，避免被其他类new出来一个对象，而Emperor自 己则可以new一个对象出来，其他类对该类的访问都可以通过getInstance获得同一个对象。 皇帝有了，臣子要出场，其类如代码清单7-2所示。 代码清单7-2 臣子类 public class Minister { public static void main(String[] args) { for(int day=0;day<3;day++){ Emperor emperor=Emperor.getInstance(); emperor.say(); } //三天见的皇帝都是同一个人，荣幸吧！ } } 臣子参拜皇帝的运行结果如下所示

To follow along with the tutorials in this book, you’ll need the following: • A Mac running the latest point release of OS X El Capitan or later: You’ll need this to be able to install the latest version of Xcode. • Xcode 8 or later: Xcode is the main development tool for iOS. You can download the latest version of Xcode for free on the Mac app store here: https:// itunes.apple.com/app/xcode/id497799835?mt=12 • Basic knowledge of Swift and iOS development. This book is about animations specifically; to understand the animation code and how the accompanying demo projects work you will need at least a basic understanding of Swift and Cocoa Touch. If you want to try things out on a physical iOS device, you’ll need a developer account with Apple, which you can obtain for free. However, all the sample projects in this book will work just fine in the iOS Simulator bundled with Xcode, so the paid developer account is completely optional.

class Pet { enum Kind { case dog case cat case guineaPig } let name: String let kind: Kind let favoriteToy: Toy? init(name: String, kind: Kind, favoriteToy: Toy? = nil) { self.name = name self.kind = kind self.favoriteToy = favoriteToy } } class Person { let pet: Pet? init(pet: Pet? = nil) { self.pet = pet }

class Pet { enum Kind { case dog case cat case guineaPig } let name: String let kind: Kind let favoriteToy: Toy? init(name: String, kind: Kind, favoriteToy: Toy? = nil) { self.name = name self.kind = kind self.favoriteToy = favoriteToy } } class Person { let pet: Pet? init(pet: Pet? = nil) { self.pet = pet }

The chapters in this section will introduce you to the very basics of programming in Swift. From the fundamentals of how computers work all the way up to language structures, you’ll cover enough of the language to be able to work with data and organize your code’s behavior. The section begins with some groundwork to get you started: • Chapter 1, Coding Essentials & Playground Basics: This is it, your whirlwind introduction to the world of programming! You’ll begin with an overview of computers and programming, and then say hello to Swift playgrounds, which are where you’ll spend your coding time for the rest of this book. Next, you’ll learn the basics of data in Swift: • Chapter 2, Expressions, Variables & Constants: You’ll start by learning some basics such as code comments, arithmetic operations, constants and variables. These are some of the fundamental building blocks of any language, and Swift is no different. • Chapter 3, Types & Operations: You’ll learn about handling different types, including strings which allow you to represent text. You’ll learn about converting between types and you’ll also be introduced to type inference which makes your life as a programmer a lot simpler. You’ll learn about tuples which allow you to make your own types made up of multiple values of any type. Once you have the basic data types in your head, it’ll be time to do things with that data: • Chapter 4, Basic Control Flow: You’ll learn how to make decisions and repeat tasks in your programs by using syntax to control the flow. You’ll also learn about Booleans, which

Gary Bradski博士是斯坦福大学人工智能实验室的顾问教授，也是Willow Garage公司机器人学研究协会的资深科学家。 Adrian Kaehler博士，Applied Minds公司的资深科学家，从事机器学习、统计建模、计算机视觉和机器人学方面的研究。 目录 · · · · · · 出版前言 译者序 写在前面的话 前言 第1章 概述 什么是OpenCV

One of the key concepts of functional programming is that of a “higher-order function”. According to Wikipedia, a higher-order function is a function that satisfies these two conditions: • It takes one or more functions as input. • It outputs a function. In Objective-C, we often use blocks as functions. We don’t have to look very far to find some higher-order functions baked into Foundation for us by Apple. Consider a simple array of numbers: 1 NSArray *array = @[@(1), @(2), @(3)]; We might want to enumerate over the contents of that array, doing something with each element. “Fine”, you say, “I’ll just write a for loop.” Stop right there, buddy. As I’ve written before, stop writing for loops. There is a higher-order function of NSArray’s that we can use, instead. This code: 1 for (NSNumber *number in array) { 2 NSLog(@"%@", number); 3 } … is equivalent to

在一个巴掌大的手机里，各个组件之间的关系错 综复杂，互相影响。硬件为固件的运行提供支撑平 台，固件掌管软件，而软件又回过头来调度硬件。如 果你能控制它们之中的哪怕一个，不就可以让手机听 命于你了吗？但App Store的插手，又为你对它们的控 制加上了重重阻力。