Introduce

Hello everyone Swift is a new programming language developed by Apple Inc. for the purpose of supporting developers in developing applications that run on iOS, OSX, and watchOS. Swift is based on the inheritance of the C and Objective-C languages.

Today I would like to share some tips to improve iOS-Swift code.

Begin

Subscripts:

Class, struct and enum can define subscript. Subscripts can be used to quickly access collections, lists, or sequences. You can use subscripts to set and retrieve data with the index, but not through other methods. For example, you access elements in an array through someArray [index] The following are two examples for using subscript to make it clearer:

Do not use subscripts:

struct Matrix {
    let rows: Int, columns: Int
    var grid: [Double]
    init(rows: Int, columns: Int) {
        self.rows = rows
        self.columns = columns
        self.grid = Array(repeatElement(0.0, count: rows * columns))
    }
    
    func getValue(row: Int, column: Int) -> Double{
        return grid[(row * columns) + column]
    }
    
    mutating func setValue(row: Int, column: Int, value: Double){
        grid[(row * columns) + column] = value
    }
}
 
var matrix = Matrix(rows: 2, columns: 2)
matrix.setValue(row: 0, column: 0, value: 1.0)
matrix.setValue(row: 0, column: 1, value: 2.0)
matrix.setValue(row: 1, column: 0, value: 3.0)
matrix.setValue(row: 1, column: 1, value: 4.0)
 
print(matrix.getValue(row: 0, column: 0)) //prints "1.0"
print(matrix.getValue(row: 0, column: 1)) //prints "2.0"
print(matrix.getValue(row: 1, column: 0)) //prints "3.0"
print(matrix.getValue(row: 1, column: 1)) //prints "4.0"
 

Use subscript

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struct Matrix {
    let rows: Int, columns: Int
    var grid: [Double]
    init(rows: Int, columns: Int) {
        self.rows = rows
        self.columns = columns
        self.grid = Array(repeatElement(0.0, count: rows * columns))
    }
    subscript(row: Int, column: Int) -> Double {
        get {
            return grid[(row * columns) + column]
        }
        set {
            grid[(row * columns) + column] = newValue
        }
    }
}
 
var matrix = Matrix(rows: 2, columns: 2)
 
matrix[0,0] = 1.0
matrix[0,1] = 2.0
matrix[1,0] = 3.0
matrix[1,1] = 4.0
 
print(matrix[0,0]) //prints "1.0"
print(matrix[0,1]) //prints "2.0"
print(matrix[1,0]) //prints "3.0"
print(matrix[1,1]) //prints "4.0"
 

Function vs Computed Property

Function (or Code)

Here we will take a simple example of two functions to calculate radius for diameter and vice versa

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func getDiameter(radius: Double) -> Double {
    return radius * 2
}
 
func getRadius(diameter: Double) -> Double {
    return diameter / 2
}
 
print(getDiameter(radius: 100)) //prints "200"
print(getRadius(diameter: 100)) //prints "50"
 

Computed Property (or Code)

Computed Property offers GET and SET. I will do the above example using the computed property

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var radius: Double = 100
var diameter: Double {
    get {
        return radius * 2
    }
    set {
        radius = newValue / 2
    }
}
 
print(diameter) //prints "200.0"
 
diameter = 100
print(radius) //prints "50.0"
 

Extension

Extension is used to add new functions to the class, struct, enum or protocol. We can extend the types without having to access the original source code. Here is an example of extention for Double to provide basic types of spacing

Use extension

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extension Double {
    var m: Double { return self }
    var km: Double { return self * 1000.0 }
    var cm: Double { return self / 100.0 }
    var mm: Double { return self / 1000.0 }
}
 
let thousandCentimeter = 1000.cm
print("Thousand centimeter is \(thousandCentimeter) meters")
// Prints "Thousand centimeter is 10.0 meters"
 
let threeKilometer  = 3.km
print("Three km is \(threeKilometer) meters")
// Prints "Three km is 3000.0 meters"
 

Do not use extension (bad code)

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func centimeterToMeter(value: Double) -> Double{
    return value / 100.0
}
 
func kilometerToMeter(value: Double) -> Double{
    return value * 1000.0;
}
 
let thousandCentimeter = 1000.0
print("Thousand centimeter is \(centimeterToMeter(value: thousandCentimeter)) meters")
// Prints "Thousand centimeter is 10.0 meters"
 
let threeKilometer  = 3.0
print("Three km is \(kilometerToMeter(value: threeKilometer)) meters")
// Prints "Three km is 3000.0 meters"
 

Ternary conditional

This operator is a special type consisting of 3 parts with a pattern question ? answer1 : answer2. This is the shortcut used to assess 1 2 courtesy based formula question is true or false. Here is an example to change the value of rowHeight based on whether header or not.

Use Ternary conditional

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let contentHeight = 40
let hasHeader = true
let rowHeight = contentHeight + (hasHeader ? 50 : 20)
print(rowHeight)
 
//prints "90"
 

Do not use Ternary conditional (or Code)

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let contentHeight = 40
let hasHeader = true
var rowHeight: Int
if hasHeader == true {
    rowHeight = contentHeight + 50
} else {
    rowHeight = contentHeight + 20
}
print(rowHeight) //prints "90"
 

Nil coalescing

The nil coalescing operator has the form a ?? b. It will unwraps an optional a if a is valid and if a is nil then the default value returned is b. Said it seems difficult to understand, so I will give an example: Assign the value colorNameToUse as userDefinedColorName if userDefinedColorName valid. If it userDefinedColorName is nil then the value will be set defaultColorName

Use Nil coalescing (or Code)

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var userDefinedColorName: String?   // defaults to nil
 
var colorNameToUse = userDefinedColorName ?? defaultColorName
print(colorNameToUse)
 
//prints "red"
// userDefinedColorName is nil, so colorNameToUse is set to the default of "red"
 
userDefinedColorName = "green"
colorNameToUse = userDefinedColorName ?? defaultColorName
print(colorNameToUse)
 
//prints "green"
// Now userDefinedColorName is "green", so colorNameToUse is set to the value of userDefinedColorName of "green"
 

Do not use Nil coalescing (or Code)

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let defaultColorName = "red"
var userDefinedColorName: String?   // defaults to nil
 
var colorNameToUse: String!
if let color = userDefinedColorName {
    colorNameToUse = color
} else {
    colorNameToUse = defaultColorName
}
print(colorNameToUse)
 
//prints "green"
//userDefinedColorName is "green", so colorNameToUse is set to the value of userDefinedColorName of "green"
 

Optional Unwrapping (if let vs guard let)

Both boys if let and guard let girls can unwrap optional. However, let's guard better when we need to check nested conditions. It will come out if you meet a conditioner that does not meet. Further guard let making its source code easier to read and easily maintain later. Here is an example to create a new user:

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let emailField = UITextField()
emailField.text = "abcd@mail.com"
let usernameField = UITextField()
usernameField.text = "vineet"
let passwordField = UITextField()
passwordField.text = "123456"
let conifrmPasswordField = UITextField()
conifrmPasswordField.text = "123456"
 

Use if let (or Bad Code)

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func loginIfLet(){
    if let email = emailField.text {
        if let username = usernameField.text {
            if let password = passwordField.text {
                if let conifrmPassword = conifrmPasswordField.text {
                    if password == conifrmPassword {
                        print("Email - \(email)")
                        print("Username - \(username)")
                        print("Password - \(password)")
                    } else {
                        print("Password didn't match with conifrm password.")
                    }
                } else {
                    print("Conifrm password is empty.")
                }
            } else {
                print("Password is empty.")
            }
        } else {
            print("Username is empty.")
        }
    } else {
        print("Email is empty.")
    }
}
loginIfLet()
 

Sử dụng guard let (or Awesome Code)

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func loginGuardLet(){
    guard let email = emailField.text else {
        print("Email is empty.")
        return
    }
    guard let username = usernameField.text else {
        print("Username is empty.")
        return
    }
    guard let password = passwordField.text else {
        print("Password is empty.")
        return
    }
    guard let conifrmPassword = conifrmPasswordField.text else {
        print("Conifrm password is empty.")
        return
    }
    if password == conifrmPassword {
        print("Email - \(email)")
        print("Username - \(username)")
        print("Password - \(password)")
    } else {
        print("Password didn't match with conifrm password.")
    }
}
loginGuardLet()
 

Generics

Generics are one of Swift's powerful features. Allows us to write flexible and easy reusable functions of any kind. Here is an example of how to write a function to swap two integers and two characters. Normally, we will write two functions for the two functions:

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func swapTwoInts(_ a: inout Int, _ b: inout Int) {
    let temporaryA = a
    a = b
    b = temporaryA
}
 
func swapTwoStrings(_ a: inout String, _ b: inout String) {
    let temporaryA = a
    a = b
    b = temporaryA
}
 
var someInt = 3
var anotherInt = 107
swapTwoInts(&someInt, &anotherInt)
print("someInt = \(someInt)")
print("anotherInt = \(anotherInt)")
/* prints
 someInt = 107
 anotherInt = 3
 */
 
var someString = "hello"
var anotherString = "world"
swapTwoStrings(&someString, &anotherString)
print("someString = \(someString)")
print("anotherString = \(anotherString)")
/* prints
 someString = world
 anotherString = hello
 */
 

Use Generics (or Code)

We only need to create a single function with any type of data

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func swapTwoValues<T>(_ a: inout T, _ b: inout T) {
    let temporaryA = a
    a = b
    b = temporaryA
}
 
var someInt = 3
var anotherInt = 107
swapTwoValues(&someInt, &anotherInt)
print("someInt = \(someInt)")
print("anotherInt = \(anotherInt)")
/* prints
 someInt = 107
 anotherInt = 3
 */
 
var someString = "hello"
var anotherString = "world"
swapTwoValues(&someString, &anotherString)
print("someString = \(someString)")
print("anotherString = \(anotherString)")
/* prints
 someString = world
 anotherString = hello
 */
 

Type safe using Enum

Enum defines a generic type for a set of related values and allows us to work on it securely.

Do not use Enum

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let directionToHead = "east"
switch directionToHead {
case "north":
    print("Lots of planets have a north")
case "south":
    print("Watch out for penguins")
case "east":
    print("Where the sun rises")
case "west":
    print("Where the skies are blue")
default:
    print("Unknown direction")
}
//prints "Where the sun rises"
 

Sử dụng enum(or Code)

Using the enum makes the code clearer and clearer

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enum CompassPoint {
    case north, south, east, west
}
let direction: CompassPoint = .east
 
switch direction {
case .north:
    print("Lots of planets have a north")
case .south:
    print("Watch out for penguins")
case .east:
    print("Where the sun rises")
case .west:
    print("Where the skies are blue")
}Tổng kết
 

So we went through some TIPs to improve our skills. Doing as many wrongs as possible will draw experience. No one but yourself pro. So everyone who shares more can leave behind comments so that those who do not know can know more. Thanks everyone.

Technology World

Sunday, October 14, 2018

Tips to increase skill for iOS developer