Swift基础教程：iOS编程入门指南

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"Swift by Tutorials" 是由 raywenderlich.com 的教程团队，由 Colin Eberhardt 和 Matt Galloway 联合创作的一本专为 iOS 开发者编写的 Swift 入门指南。该教程版权属于 Razeware LLC，强调所有内容未经版权所有者书面许可不得复制或分发，旨在以"原样"形式提供，不附带任何形式的明示或暗示保证，包括但不限于适销性、特定用途的适用性和非侵权性。作者和版权所有者不对因软件使用产生的任何索赔、损害或其他责任负责。本书分为三个核心章节： 1. **语言基础I**：本章作为入门起点，介绍了 Swift 语言的基本概念，帮助读者理解编程语言的基础结构，如变量、数据类型、控制流（条件语句、循环）、函数和输入/输出等。这些基础知识是构建 iOS 应用程序的基础，对于初学者来说至关重要。 2. **语言基础II**：在第二章中，作者继续深入探讨 Swift 的细节，可能涵盖更高级的主题，如面向对象编程（OOP）的核心原理、类和对象的概念、继承、封装和多态性。通过实例演示和实践项目，读者将学习如何组织代码，以及如何利用这些 OOP 技术来设计和实现复杂的 iOS 应用。 3. **Chapter 3: Classes** - 这是本书的重要部分，主要聚焦于 Swift 中的类和结构体（Structs），讲解如何创建自定义类型，包括如何定义属性和方法，以及它们在 iOS 开发中的实际应用。读者会学习如何使用这些类来构建可复用的组件，提高代码质量和应用程序的模块化。整个教程旨在通过清晰易懂的步骤和逐步实践，使读者逐步掌握 Swift 语言和 iOS 开发所需的关键技能，无论你是初次接触编程还是希望提升现有技能，这本书都提供了实用的学习资源。同时，读者应始终牢记，所有的源代码和教学材料仅供个人学习和参考，商业使用必须获得授权。

Swift by Tutorials Chapter 1: Language Basics I

raywenderlich.com Page 16

Open Xcode, select File\New Playground…, select the iOS platform and save the

file wherever you like:

A playground is a single Swift file that the template populates as follows:

As you enter your Swift code on the left-hand side of the view, the right-hand side

automatically displays the value of assignments and other useful hints about the

resulting application state. You don’t have to explicitly invoke a Build command

after making a change. In a playground, Xcode continually builds and executes your

code as you type.

Wouldn’t a playground be an excellent place to practice your Swift skills?

Swift by Tutorials Chapter 1: Language Basics I

raywenderlich.com Page 19

println(greeting)

This causes the compiler to report an error, type 'String' does not conform to

protocol 'IntegerLiteralConvertible', at the second line.

Type inference doesn’t weaken your application in any way; it simply saves

keystrokes by removing the need to specify types that are obvious to the compiler

(and hopefully to you). The simple example above shows type inference when

assigning literal values, but it will work everywhere within the language—for

example, when you create a variable and assign it a value from a function.

PRO TIP: We encourage you to use type inference extensively, as it results in

more concise and thus more readable code. However, if there is any instance

where you think adding an explicit type to a variable declaration would

enhance readability, there is certainly nothing wrong with doing so!

Let’s do some simple string manipulation. Update the code as follows:

var greeting = "Hello"

greeting = greeting + " World"

println(greeting)

The console output is now “Hello World” (surely you didn’t need a compiler to tell

you that!).

Swift strings are mutable—that is, you can change their values—where the

mutations have a much simpler syntax than their NSMutableString counterparts.

For example, you could change the above to use the more compact += compound

assignment operator.

There are many times you want to create a value that does not change. Creating

these values as variables is inherently unsafe since accidental assignments can and

do happen.

Swift makes it easy to change a variable into a constant. Update the first line of

code as follows:

let greeting = "Hello"

This results in an error at the second line of code: cannot assign to 'let' value

'greeting'.

You can control the mutability of the built-in Swift types (e.g., String, Int,

Dictionary) by using either the let or var keywords at the point of declaration.

This is in stark contrast to Objective-C and many other languages, where some

type implementations are inherently mutable, such as NSMutableArray, and some

are not, such as NSArray.

Swift by Tutorials Chapter 1: Language Basics I

raywenderlich.com Page 20

PRO-TIP: You should define values as constants wherever possible. This not

only makes your code more robust, it also allows the compiler to further

optimize your code, improving execution times. Thus, you will probably find

yourself using let far more often than var.

The use of let in order to make an instance of a type immutable isn’t restricted to

the built-in Swift types. Any structures (structs) that you define yourself also have

this behavior; however there are some subtle differences between constant

structures and classes. You can read more on this in Chapter 3, “Classes and

Structs”.

Change greeting back to a variable by changing the let to var, then add the

following line just before the println statement:

greeting.append(Character("!"))

This appends an exclamation mark to the end of the string, with the console

outputting the result, “Hello World!”.

The Swift String type has API methods like the above that allow you to manipulate

their values. However, these are quite limited in number. Fortunately, the Swift

String type is bridged to the Objective-C NSString type, providing all the API

methods with which you are no doubt familiar if you’ve used Objective-C.

To introduce these methods, update your playground as follows:

import Foundation

var greeting = "hello world".capitalizedString

println(greeting)

This results in the output “Hello World”.

With the first statement, you import the Foundation framework, which includes

NSString. This adds capitalizedString to Swift’s String.

Why not experiment with some of the other NSString API methods within the

playground? You can even append strings using stringByAppendingString if you

aren’t keen on the more compact Swift style!

import Foundation

var greeting = "hello".stringByAppendingString(" world")

println(greeting)

Finally, the Swift String is a value type. As a result, when you assign a string to a

variable, a constant, or pass it as an argument to a function, its value is copied.

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