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- Herausgeber: Packt Publishing
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Develop the skills required to create compelling, maintainable, and robust iOS and OS X apps with Swift
About This Book
- Write expressive, understandable, and maintainable Swift 2 code with this hands-on tutorial
- Unveil the complex underpinnings of Swift to turn your app ideas into reality
- This book is packed with real-life examples to help you implement concepts as you learn
Who This Book Is For
If you are looking to build iOS or OS X apps using the most modern technology, this book is ideal for you. You will find this book especially useful if you are new to programming or if you are yet to develop for iOS or OS X. No prior programming exposure is required.
What You Will Learn
- Form a solid understanding of the Swift 2 language
- Get to know the practical aspects of how a computer program actually works
- Understand the paradigms used by Apple's frameworks so you are not intimidated by them
- Utilize the vast resources written in Objective-C to better inform your Swift programming
- Develop a basic portfolio of Swift code by learning the critical concepts
- Experience both object-oriented and functional programming
- Get to know the new coding techniques made available by Swift 2
- Discover resources to ensure you never stop becoming a better developer
In Detail
Swift is Apple's new programming language and the future of iOS and OS X app development. It is a high-performance language that feels like a modern scripting language. On the surface, Swift is easy to jump into, but it has complex underpinnings that are critical to becoming proficient at turning an idea into reality.
This book is an approachable, step-by-step introduction into programming with Swift for everyone. It begins by giving you an overview of the key features through practical examples and progresses to more advanced topics that help differentiate the proficient developers from the mediocre ones. It covers important concepts such as Variables, Optionals, Closures, Generics, and Memory Management. Mixed in with those concepts, it also helps you learn the art of programming such as maintainability, useful design patterns, and resources to further your knowledge. This all culminates in writing a basic iOS app that will get you well on your way to turning your own app ideas into reality.
Style and approach
This is an approachable, step-by-step guide to programming in Swift 2. Each topic is separated into compressible sections that are full of practical examples and easy-to-understand explanations. Each section builds on the previous topics so you can develop a proficient and comprehensive understanding of app development in Swift 2.
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Seitenzahl: 404
Veröffentlichungsjahr: 2016
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Table of Contents
Learning Swift Second Edition
Learning Swift Second Edition
Copyright © 2016 Packt Publishing
All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.
Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.
Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.
First published: June 2015
Second edition: March 2016
Production reference: 1170316
Published by Packt Publishing Ltd.
Livery Place
35 Livery Street
Birmingham B3 2PB, UK.
ISBN 978-1-78588-751-2
www.packtpub.com
Credits
Author
Andrew J Wagner
Reviewer
Guan Gui
Commissioning Editor
Kartikey Pandey
Acquisition Editors
Vivek Anantharaman
Chaitanya Nair
Content Development Editor
Viranchi Shetty
Technical Editor
Saurabh Malhotra
Copy Editors
Kevin McGowan
Sneha Singh
Project Coordinator
Izzat Contractor
Proofreader
Safis Editing
Indexer
Hemangini Bari
Production Coordinator
Shantanu N. Zagade
Cover Work
Shantanu N. Zagade
About the Author
Andrew J Wagner is a software developer who concentrates on iOS development and backend web services. He has a degree in computer engineering from Rensselaer Polytechnic Institute, New York. Currently, he works for a development shop named Chronos Interactive based in Denver, CO. He has experience of working with and for large-scale and small-scale companies, as well as running his own contracting and app companies. He is passionate about using computers as a creative outlet and writing software that is beautiful in implementation, functionality, and experience.
When he isn't working or spending time with friends and family, he writes for his blog at http://drewag.me.
I would like to thank my friends and family for being there for me as support for both my troubles and triumphs. Without their encouragement, I would not have finished this book or achieved any of the other things in my life that make me proud. An especially big thanks to my parents, Fern and Joe, for continually providing me with the tools I need to do the things I love.
About the Reviewer
Guan Gui graduated from the University of Melbourne. He implemented the first system of its kind for beekeepers using satellite sensory data to help them deploy their honeybees better. He is also a big fan of Apple. He started his own open source project—Uni Call (unicall.guiguan.net) for OS X. While his research focus is on machine learning, he enjoys the more practical side of CS: developing apps using Swift and JavaScript. Currently, he is trying to set his own start-up. Big ideas to change the world always spin in his head!
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Preface
This book will help you to get started with Swift in no time. It helps you understand the nuances of iOS programming not only from a conceptual but also from an implementation perspective. This book is an invaluable resource if you are looking forward to exploring the world of iOS application programming.
What this book covers
Chapter 1, Introducing Swift, will take the reader through the process of installing Swift and running their first Swift program, in order to expose its power right away.
Chapter 2, Building Blocks - Variables, Collections, and Flow Control, introduces you to the various built-in mechanisms Swift has for representing complex information in expressive and accessible ways, with the help of a real-world example.
Chapter 3, One Piece at a Time - Types, Scopes, and Projects, introduces the tools necessary to closely model the real world with code. It will teach you how to define your own custom types using structures, classes, and enumerations. It also explores the concept of scope and access control.
Chapter 4, To Be or Not To Be - Optionals, focuses on a special and critical type in Swift, called optionals. It includes a detailed explanation of how optionals work and how they can be used, which turns a seemingly complex topic into a very intuitive concept.
Chapter 5, A Modern Paradigm - Closures and Functional Programming, introduces you to a new way of thinking about code called functional programming. We learn how Swift supports this technique and how we can apply it to our programs to make it even more understandable and expressive.
Chapter 6, Make Swift Work For You - Protocols and Generics, describes what generics and protocols are and how they can provide power and safety at the same time.
Chapter 7, Everything Is Connected - Memory Management, dives deeper into the inner-workings of Swift. We discuss how a computer stores information and how we can use that knowledge in combination with some new tools in Swift, to ensure that our code remains responsive and minimizes its effect on battery life.
Chapter 8, Paths Less Traveled – Error Handling, goes into gracefully handling error situations in Swift with error throwing and catching.
Chapter 9, Writing Code the Swift Way - Design Patterns and Techniques, introduces the reader to the art of programming by taking them through a number of specific design patterns that help reduce the complexity of code.
Chapter 10, Harnessing the Past - Understanding and Translating Objective-C, develops a basic understanding of Objective-C with a focus on how it compares to Swift. This allows the reader to make use of the vast resources that exist in Objective-C to help with their Swift development.
Chapter 11, A Whole New World - Developing an App, focuses on explaining the process of creating a real world iOS application, with the help of an example.
Chapter 12, What's Next? - Resources, Advice, and the Next Steps, discusses how to move forward to become the best app developer you possibly can. It provides a list of resources and advice the reader can use to continue their Swift and app development learning process.
What you need for this book
To run the code in this book, you will need Xcode 7.2.
Who this book is for
If you want to build iOS or OS X apps using the most modern technology, this book is ideal for you. Learning Swift will place you into a small developer community that will explode in demand when all the development for Apple's platforms transitions to it. You will find this book especially useful if you are new to programming or if you have yet to develop for iOS or OS X.
Conventions
In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.
When mentioning pieces of code in text we will use the style as follows: "You can see that "Hello, playground" was indeed stored in the variable.
If the code is longer it will presented as a block as follows:
New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "Now, click on Connect on the Remote Desktop Viewer". Keyboard shortcuts will be displayed using the key style.
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Questions
If you have a problem with any aspect of this book, you can contact us at <[email protected]>, and we will do our best to address the problem.
Chapter 1. Introducing Swift
What are you trying to achieve by reading this book? Learning Swift can be fun, but most of us are trying to achieve something bigger. There is something we want to create, a career we want to follow, or maybe something else entirely. Whatever that goal is, I encourage you to keep it in mind as you read this book. It will be much easier for you to learn, from this or any other resource, if you can always relate it to your goal.
With that in mind, before we dive into learning Swift, we have to understand what it really is and how it will help us in achieving our goals. We also need to move forward with an effective learning technique and get a taste of what is to come. To do all of that, we will cover the following topics in this chapter:
Defining our goals for this book
Swift is a programming language developed by Apple primarily to allow developers to continue to push their platforms forward. It is their attempt to make iOS, OS X, watchOS, and tvOS app development more modern, safe, and powerful.
However, Apple has also released Swift as Open Source and begun an effort to add support for Linux with the intent to make Swift even better and a general purpose programming language available everywhere. Some developers have already begun using it to create command-line scripts as a replacement/supplement of the existing scripting languages, such as Python or Ruby and many can't wait to be able to share some of their app code with Web backend code. Apple's priority, at least for now, is to make it the best language possible, to facilitate app development. However, the most important thing to remember is that modern app development almost always requires pulling together multiple platforms into a single-user experience. If a language could bridge those gaps and stay enjoyable to write, safe, and performant, we would have a much easier time making amazing products. Swift is well on its way to reach that goal.
Now, it is important to note that learning Swift is only the first step towards developing. To develop for a device, you must learn the programming language and the frameworks the device maker provides. Being skilled with a programming language is the foundation of getting better at using frameworks and ultimately building apps.
Developing software is like building a table. You can learn the basics of woodworking and nail a few pieces of wood together to make a functional table, but you are very limited in what you can do because you lack advanced woodworking skills. If you want to make a truly great table, you need to step away from the table and focus first on developing your skill set. The better you are at using the tools, the greater the number of possibilities that open up to you to create a more advanced and higher quality piece of furniture. Similarly, with a very limited knowledge of Swift, you can start to piece together a functional app from the code you find online. However, to really make something great, you have to put the time and effort into refining your skill set with the language. Every language feature or technique that you learn opens up more possibilities for your app.
That being said, most developers are driven by a passion to create things and solve problems. We learn best when we can channel our passions into truly improving ourselves and the world around us. We don't want to get stuck learning the minutia of a language with no practical purpose.
The goal of this book is to develop your skills and confidence to dive passionately into creating compelling, maintainable, and elegant apps in Swift. To do that, we will introduce the syntax and features of Swift in a practical way. You will build a rich toolset, while seeing that toolset put to real world usage. So, without further ado, let's jump right into setting up our development environment.
Setting up the development environment
In order to use Swift, you will need to run OS X, the operating system that comes with all Macs. The only piece of software that you will need is called Xcode (version 7 and higher). This is the environment that Apple provides, which facilitates development for its platforms. You can download Xcode for free from the Mac App Store at www.appstore.com/mac/Xcode.
Once downloaded and installed, you can open the app and it will install the rest of Apple's developer tool components. It is as simple as that! We are now ready to run our first piece of Swift code.
Understanding playgrounds
A playground is not truly a program. While it does execute code like a program, it is not really useful outside of the development environment. Before we can understand what the playground is doing for us, we must first understand how Swift works.
Swift is a compiled language, which means that for Swift code to be run, it must first be converted into a form that the computer can actually execute. The tool that does this conversion is called a compiler. A compiler is actually a program and it is also a way to define a programming language.
The Swift compiler takes the Swift code as input and, if it can properly parse and understand the code, outputs machine code. Apple developed the Swift compiler to understand the code according to a series of rules. Those rules are what define the Swift programming language and those rules are what we are trying to learn, when we say we are learning Swift.
Once the machine code is generated, Xcode can wrap the machine code up inside an app that users can run. However, we are running Swift code inside our playground, so clearly building an app is not the only way to run code; something else is going on here.
Every time you make a change to a playground, it automatically tries to compile your code. If it is successful, instead of wrapping up the machine code in an app to be run later, it runs the code immediately and shows you the results. If you had to do this process yourself, you would first have to consciously make the decision to build the code into an app and then run it when you wanted to test something. This would be a huge waste of time; especially, if you write an error that you don't catch until the moment you decide to actually run it. The quicker you can see the result of a code change, the faster you will be at developing the code and the fewer mistakes you will make.
For now, we will be developing all of our code inside a playground because it is a fantastic learning environment. Playgrounds are even more powerful than what we have seen so far and we will see that as we explore deeper into the Swift language.
We are just about ready to get to the meat of learning Swift, but first let's take a moment to make sure that you can get the most out of this book.
Learning with this book
The learning process of this book follows very closely to the philosophy behind playgrounds. You will get the most out of this book if you play around with the code and ideas that we discuss. Instead of just passively reading through this, glancing at the code, put the code into a playground, and observe how it really works. Make changes to the code, try to break it, try to extend it, and you will learn far more. If you have a question, don't default to looking up the answer, try it out.
At its core, programming is a creative exercise. Yes, it requires the ability to think logically through a problem, but nine times out of ten there is no right way there is no correct answer. Technology is pushed by those of us who won't settle for the accepted solution, who aren't OK with following a fixed set of instructions, who want to push the boundaries. As we move forward in learning Swift, make this book and Swift work for you by not taking everything at face value.
Summary
We're off to a good start. We've gone over how Swift is a language designed primarily for app development, which often includes multiple different platforms. We already ran our first code and learned a little bit about how a computer runs it indirectly by first compiling it into a form it understands how to run. Most importantly, we've learned that you will learn best from this book by having a goal to work towards and by playing around with the concepts as you read along. So let's get started!
Next, we will start breaking down the basics of Swift and then put them together to make our first program.
Printing to the console
It is very useful to write output to a log so that you can trace the behavior of code. As a codebase grows in complexity, it gets hard to follow the order in which things happen and exactly what the data looks like as it flows through the code. Playgrounds help a lot with this but it is not always enough.
In Swift, this process is called printing to the console. To do this, you use something called print. It is used by writing print followed by text surrounded by parentheses. For example, to print Hello World! to the console, the code would look like this:
If you put that code in a playground, you would see Hello World! written in the results pane. However, this is not truly the console. To view the console, you can go to View | Debug Area | Show Debug Area. A new view will appear at the bottom of the window and it will contain all text the code has printed to the console:
Not only can you print static text to the console, you can also print out any variable. For example, if you wanted to print out the name variable, you would write:
You can even use a feature of Swift called string interpolation to insert variables into a string, like this:
At any point in a string literal, even when not printing, you can insert the results of the code by surrounding the code with \( and ). Normally this would be the name of a variable but it could be any code that returns a value.
Printing to the console is even more useful when we start using more complex code.
Control flow
A program wouldn't be very useful if it were a single fixed list of commands that always did the same thing. With a single code path, a calculator app would only be able to perform one operation. There are a number of things we can do to make an app more powerful and collect the data to make decisions as to what to do next.
Conditionals
The most basic way to control the flow of a program is to specify code that should only be executed if a certain condition is met. In Swift, we do that with an if statement. Let's look at an example:
Semantically, the preceding code reads; if the number of invitees is greater then 20, print 'Too many people invited". This example only executes one line of code if the condition is true, but you can put as much code as you like inside the curly brackets ({}).
Anything that can be evaluated as either true or false can be used in an if statement. You can then chain multiple conditions together using an else if and/or an else:
Each condition is checked from top to bottom until a condition is satisfied. At that point, the code block is executed and the remaining conditions are skipped, including the final else block.
As an exercise, I recommend adding an additional scenario to the preceding code in which, if there were exactly zero invitees, it would print "One is the loneliest number". You can test out your code by adjusting how many invitees you add to the invitees declaration. Remember that the order of the conditions is very important.
As useful as conditionals are, they can become very verbose if you have a lot of them chained together. To solve this type of problem, there is another control structure called a switch.
Switches
A switch is a more expressive way of writing a series of if statements. A direct translation of the example from the conditionals section would look like this:
A switch consists of a value and a list of conditions for that value with the code to execute if the condition is true. The value to be tested is written immediately after the switch command and all of the conditions are contained in curly brackets ({}). Each condition is called a case. Using that terminology, the semantics of the preceding code is "Considering the number of invitees, in the case that it is greater than 20, print "Too many people invited", otherwise, in the case that it is less than or equal to three, print "Too many people invited", otherwise, by default print "Just right".
This works by creating a temporary constant x that is given the value that the switch is testing. It then performs a test on x. If the condition passes, it executes the code for that case and then exits the switch.
Just like in conditionals, each case is only considered if all of the previous cases are not satisfied. Unlike conditionals, all the cases need to be exhaustive. That means that you need to have a case for every possible value that the variable being passed in could be. For example, invitees.count is an integer, so it could theoretically be any value from negative infinity to positive infinity.
The most common way to handle that is by using a default case as designated by the default keyword. Sometimes, you don't actually want to do anything in the default case, or possibly even in a specific case. For that, you can use the break keyword, as shown here:
Note that the default case must always be the last one.
We have seen so far that switches are nice because they enforce the condition of being exhaustive. This is great for letting the compiler catch bugs for you. However, switches can also be much more concise. We can rewrite the preceding code like this:
Here, we have described each case as a range of possible values. The first case includes all of the values between and including 0 and 3. This is way more expressive than using a where
