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首页"专业iOS开发者的Swift学习笔记: 借鉴专业技巧与提示"

"专业iOS开发者的Swift学习笔记: 借鉴专业技巧与提示"

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Swift Notes for Professionals is a comprehensive educational resource designed specifically for professional iOS developers. This English-language book, entitled "SwiftNotes for ProfessionalsSwift™," is available for free on GoalKicker.com and offers 200 pages of expert tips and tricks for mastering Swift programming. Readers can expect to find a wealth of valuable information within this book, including a wide range of professional hints and tricks that are sure to elevate their iOS development skills. With its focus on practical, real-world applications, Swift Notes for Professionals is an essential resource for anyone looking to deepen their understanding of Swift programming and improve their proficiency in iOS development. It's important to note that this book is an unofficial, educational publication and is not affiliated with any official Swift™ group(s) or company(s). Furthermore, all trademarks and registered trademarks mentioned in the book belong to their respective owners. In summary, Swift Notes for Professionals is a must-read for any professional iOS developer seeking to expand their expertise in Swift programming. With its 200 pages of valuable insights and practical advice, this book is a valuable asset for anyone looking to advance their career in iOS development. Get your copy today and take your programming skills to the next level.

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GoalKicker.com – Swift™ Notes for Professionals 7

Congratulations! You've created your ﬁrst program in Swift!

Section 1.3: Your ﬁrst program in Swift Playgrounds app on

iPad

Swift Playgrounds app is a great way to get started coding Swift on the go. To use it:

1- Download Swift Playgrounds for iPad from App Store.

GoalKicker.com – Swift™ Notes for Professionals 8

2- Open the app.

3- In the My Playgrounds tab, tap + on the top left corner and then select Blank template.

4- Enter your code.

5- Tap Run My Code to run your code.

6- At the front of each line, the result will be stored in a small square. Tap it to reveal the result.

7- To step slowly through code to trace it, tap the button next to Run My Code.

Section 1.4: Installing Swift

First, download the compiler and components.

Next, add Swift to your path. On macOS, the default location for the downloadable toolchain is

/Library/Developer/Toolchains. Run the following command in Terminal:

export PATH=/Library/Developer/Toolchains/swift-latest.xctoolchain/usr/bin:"${PATH}"

On Linux, you will need to install clang:

$ sudo apt-get install clang

If you installed the Swift toolchain to a directory other than the system root, you will need to run the following

command, using the actual path of your Swift installation:

$ export PATH=/path/to/Swift/usr/bin:"${PATH}"

You can verify you have the current version of Swift by running this command:

$ swift --version

Section 1.5: Optional Value and Optional enum

Optionals type, which handles the absence of a value. Optionals say either "there is a value, and it equals x" or

"there isn't a value at all".

www.dbooks.org

GoalKicker.com – Swift™ Notes for Professionals 9

An Optional is a type on its own, actually one of Swift’s new super-powered enums. It has two possible values, None

and Some(T), where T is an associated value of the correct data type available in Swift.

Let's have a look at this piece of code for example:

let x: String? = "Hello World"

if let y = x {

print(y)

}

In fact if you add a print(x.dynamicType) statement in the code above you'll see this in the console:

Optional<String>

String? is actually syntactic sugar for Optional, and Optional is a type in its own right.

Here's a simpliﬁed version of the header of Optional, which you can see by command-clicking on the word Optional

in your code from Xcode:

enum Optional<Wrapped> {

/// The absence of a value.

case none

/// The presence of a value, stored as `Wrapped`.

case some(Wrapped)

}

Optional is actually an enum, deﬁned in relation to a generic type Wrapped. It has two cases: .none to represent the

absence of a value, and .some to represent the presence of a value, which is stored as its associated value of type

Wrapped.

Let me go through it again: String? is not a String but an Optional<String>.The fact that Optional is a type

means that it has its own methods, for example map and flatMap.

GoalKicker.com – Swift™ Notes for Professionals 10

Chapter 2: Variables & Properties

Section 2.1: Creating a Variable

Declare a new variable with var, followed by a name, type, and value:

var num: Int = 10

Variables can have their values changed:

num = 20 // num now equals 20

Unless they're deﬁned with let:

let num: Int = 10 // num cannot change

Swift infers the type of variable, so you don't always have to declare variable type:

let ten = 10 // num is an Int

let pi = 3.14 // pi is a Double

let floatPi: Float = 3.14 // floatPi is a Float

Variable names aren't restricted to letters and numbers - they can also contain most other unicode characters,

although there are some restrictions

Constant and variable names cannot contain whitespace characters, mathematical symbols, arrows,

private-use (or invalid) Unicode code points, or line- and box-drawing characters. Nor can they begin with

a number

Source developer.apple.com

var π: Double = 3.14159

var : String = "Apples"

Section 2.2: Property Observers

Property observers respond to changes to a property's value.

var myProperty = 5 {

willSet {

print("Will set to \(newValue). It was previously \(myProperty)")

}

didSet {

print("Did set to \(myProperty). It was previously \(oldValue)")

}

myProperty = 6

// prints: Will set to 6, It was previously 5

// prints: Did set to 6. It was previously 5

willSet is called before myProperty is set. The new value is available as newValue, and the old value is still

available as myProperty.

www.dbooks.org

GoalKicker.com – Swift™ Notes for Professionals 11

didSet is called after myProperty is set. The old value is available as oldValue, and the new value is now

available as myProperty .

Note: didSet and willSet will not be called in the following cases:

Assigning an initial value

Modifying the variable within its own didSet or willSet

The parameter names for oldValue and newValue of didSet and willSet can also be declared to increase

readability:

var myFontSize = 10 {

willSet(newFontSize) {

print("Will set font to \(newFontSize), it was \(myFontSize)")

}

didSet(oldFontSize) {

print("Did set font to \(myFontSize), it was \(oldFontSize)")

}

Caution: While it is supported to declare setter parameter names, one should be cautious not to mix

names up:

willSet(oldValue) and didSet(newValue) are entirely legal, but will considerably confuse readers

of your code.

Section 2.3: Lazy Stored Properties

Lazy stored properties have values that are not calculated until ﬁrst accessed. This is useful for memory saving

when the variable's calculation is computationally expensive. You declare a lazy property with lazy:

lazy var veryExpensiveVariable = expensiveMethod()

Often it is assigned to a return value of a closure:

lazy var veryExpensiveString = { () -> String in

var str = expensiveStrFetch()

str.expensiveManipulation(integer: arc4random_uniform(5))

return str

}()

Lazy stored properties must be declared with var.

Section 2.4: Property Basics

Properties can be added to a class or struct (technically enums too, see "Computed Properties" example). These

add values that associate with instances of classes/structs:

class Dog {

var name = ""

}

In the above case, instances of Dog have a property named name of type String. The property can be accessed and

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