Maxime Defauw. Learning Swift

Transcription

1 Maxime Defauw Learning Swift SAMPLE CHAPTERS

2 1 Introduction Begin at the beginning, the King said, very gravely, and go on till you come to the end: then stop. Lewis Carroll, Alice in Wonderland

3 Hi and welcome to this Swift book! In this course you ll learn the brand-new Swift language. Apple introduced it at the WWDC 2014, which is an abbreviation for the Apple Worldwide Developer Conference, an annual conference where Apple showcases its new products. This time, Apple surprised us all by introducing two unexpected products: the Apple Watch and Swift, a brand-new programming language that has a lot of new features and capabilities. But what is a programming language? Computers don t understand English, French or whatever language that we, the people, speak. A programming language is kind of a special language programmers it use to communicate with a computer. Programs are in fact a set of instructions which a computer has to follow There are a lot of different types of programming languages, but I won t bother you here with the explanation of the differences between them. The best way to learn a foreign language is by actually speaking it. This is the same for programming languages! So, what are you waiting for? Let s start! Maxime Defauw ii

4 To Françoise Granny Mattelaer Thanks for helping me writing my book. And for the delicious lunches every Monday. iii

5 2 Installing Xcode The beginning is always today. Mary Wollstonecraft

6 Let s begin by installing Xcode. Xcode is an IDE or Integrated Development Environment. It is a set of development tools used to create IOS and Mac OS X applications. Xcode 6, the latest version of Xcode at the time of writing, is the one we will use in this book. You will need to install Xcode on your Mac in order to complete the tutorials of this book. Of course, it is completely free! You can download Xcode on the Apple Developer site or on the Mac App Store. (Fig. 2-1) You can find the Mac App Store in your Applications folder. Xcode on the Mac App Store. Click the Get button under the Xcode logo. (Fig 2-1) 5

7 Once Xcode is downloaded and installed, open it up. In most cases, Xcode will be downloaded in your Applications Folder. If not, you could search for it with spotlight (The magnifying glass at the top right corner of your mac) or Finder You will be greeted by this window (Fig. 2-2) Greeting window when opening Xcode (Fig. 2-2) You have different options presented in the launching screen. A new feature that comes with Swift is Playgrounds. A Playground is an interactive environment that allows you to try out new code and ideas and see the results in real time instead of having to create a real project. This sounds good for learning! Let s create one! Click on Get started with a playground. This brings up a new window. (Fig. 2-3) 6

8 Create your playground (Fig. 2-3) Choose a name for your playground. I ll just leave it with MyPlayground. Set ios for platform and click Next. Select a place where you want your playground to be saved and click Create. Xcode automatically opens our Playground file. This is where you will write your first lines of code! As you can see, there s already some code generated for you. It looks strange, right? In the next chapter, we will analyze this line-by-line and write our first lines of code! 7

9 3 Types The first step is you have to say that you can. Will Smith

10 Comments Let s start where we left in the last chapter. If it isn t already, open up the playground we previously created. When you make a playground file, there is by default some code generated. What does it all mean? Let s take a closer look. // Playground - noun: a place where people can play import UIKit var str = "Hello, playground" The first line is what is called a comment. It is just a little explanation the coder or the developer wrote to make things a little easier. You can write everything you want in a comment. For example this is a piece of code that calculates three minus five or I left here yesterday, and I still have to add a calculator code. This is extremely useful when you work in team. For instance you could write something about the piece of code you made, and send it directly to your team member. Or if you have made a little program, and want to adapt it some weeks later, you could have written a comment about your code so you ll still understand what you wrote some weeks later. In Swift, comments can be made in two different ways. The first way is by typing two slashes followed by your comment. The second way, which is often used for longer comment sections, is by opening the comment section with a /* and closing it with a */. // This is a single line comment /* This is a longer comment section. Here, you can type longer comments that consist of one or more lines */ Try it out! Type something about this book in your playground. It is very good and educational to code with me. So try out everything you learn in this book inside your playground. This way, you will understand and memorize everything better. 9

11 Variables Before introducing you to the second line of code, I want to explain how a program works. When you write code, you decide what you want the computer to do by making instructions it has to follow. Next you run the instructions through the compiler, which is yet another program that converts your instructions into code your computer can understand. Now the machine can execute your application. swift code var str = hello println(str) compiler computer code The second line import UIKit tells the compiler to include a certain file of framework in your project (in this case the UIKit framework). UIKit provides the crucial infrastructure needed to construct and manage IOS apps. Frameworks represent big chunks of code you won t have to rewrite every time you make a new project. For example, the UIKit provides support for handling touch- and motion-based events on your iphone, ipad or ipod Touch. Without this framework, programing would be very repetitive, boring and tedious as you d have to retype all this code over and over again when creating a new app. Let s jump to the third line! var str = "Hello, playground is a variable. Think of it as a box that serves as a storage for some content like letters and numbers: str is the box and Hello, playground is its content. You can create a variable by typing var followed by the name or identifier of the variable. Assigning a value to a variable is done by typing the variable identifier or the variable name followed by an equals sign and its value. var mynumber = 5.2 var mystring = "Hello World!" Here we create two variables mynumber which is equal to 5.2 and mystring which contains the value Hello World! 10

12 You don t have to assign a value to a variables directly when you create it. It is possible to create a variable and assign it s value later on. But if you do so, you will have to set the type of the variable explicitly. For example, if you want to create a variable that holds an Integer value (a whole number like 1, 6 or -254), you ll have to specify the variable to hold an integer. You do this by typing a colon ( : ) after the identifier followed by the type of the variable. var myinteger: Int myinteger = 5 However if you assign its value directly, Swift is powerful enough to recognize the type of variable and you don t have to specify the type. Observe the difference between the two. var explicitinteger: Int = 5 var implicitinteger = 4 There are different types of variables in Swift. Here is a list of the basic data types. Data type Explanation Example Int Is used for whole numbers -4, 6, 185, 0 Float Is used for numbers with decimal points 9.6, , Double Is used for bigger numbers with decimal points , -652, String Ordered sequences of characters Hello, how are doing? Bool Means true or false True, False When examining this table above, you may have some questions such as what is the difference between a float and a double? or What is a bool used for? As the name implies, a double has two times the precision of a float. This means that the result of a calculation stored in a float can be 9,00..., though if it s stored in a double it would be 8,99... A bool or boolean is a variable type that can either be true or false. It is used to represent the truth values in an expression. For instance if you want to check in code if 5 is greater than 4, the bool would be true. You ll learn more about bools in CHAPTER NAME. 11

13 Constants A variable is, as the name suggest, variable. This means that if you assign a value to a variable, it can be changed later on in the program. A constant on the contrary is, again as the name suggest, constant. This means that once you assign a value to it, it can never be changed. In Swift you create constants just like you create variables, but instead of writing var before the identifier, you write let. let myname = "Maxime" var myage = 15 // Next year, my age becomes greater, but my name stays the same. That s why myname is constant and myage is a variable myage = 16 // Now myage is equal to 16 Why would you want to use a constant? The answer is simple: for safer and cleaner code and performance optimization. If you ever want to create a box for a value, the rule is simple: if it can be a constant, make it a constant. Otherwise make it a variable. 12

14 Challenge The best way of learning a new programming language is not by only reading a book or watching videos online. You have to exercise what you ve learned! This is why there will be some challenges at the end of each chapter. Some are easy, others may be more difficult. But it is very important you try to succeed every challenge at its best! These are the challenges for this chapter: Create a new playground file named Challenge Chapter 3 Make two variables; one implicit Double, and one explicit Int. Create a constant with your name Add a comment beneath explaining the difference between a float and a double. The solutions for this chapter can be found here l=0 If you completed these challenges, you can officially code! 13