Creating an extension

Add a new swift file with File > New > File... > iOS > Source > Swift File. You can call it what you want.

The general naming convention is to call it TypeName+NewFunctionality.swift.

Example 1 - Double

Double+Conversions.swift

import Swift // or Foundation


extension Double {


func celsiusToFahrenheit() -> Double {
return self * 9 / 5 + 32
}


func fahrenheitToCelsius() -> Double {
return (self - 32) * 5 / 9
}
}

Usage:

let boilingPointCelsius = 100.0
let boilingPointFarenheit = boilingPointCelsius.celsiusToFahrenheit()
print(boilingPointFarenheit) // 212.0

Example 2 - String

String+Shortcuts.swift

import Swift // or Foundation


extension String {


func replace(target: String, withString: String) -> String {
return self.replacingOccurrences(of: target, with: withString)
}
}

Usage:

let newString = "the old bike".replace(target: "old", withString: "new")
print(newString) // "the new bike"

Here are some more common String extensions.

Example 3 - UIColor

UIColor+CustomColor.swift

import UIKit


extension UIColor {


class var customGreen: UIColor {
let darkGreen = 0x008110
return UIColor.rgb(fromHex: darkGreen)
}


class func rgb(fromHex: Int) -> UIColor {


let red =   CGFloat((fromHex & 0xFF0000) >> 16) / 0xFF
let green = CGFloat((fromHex & 0x00FF00) >> 8) / 0xFF
let blue =  CGFloat(fromHex & 0x0000FF) / 0xFF
let alpha = CGFloat(1.0)


return UIColor(red: red, green: green, blue: blue, alpha: alpha)
}
}

See here also.

Usage:

view.backgroundColor = UIColor.customGreen

Notes

• Once you define an extension it can be used anywhere in your app just like the built in class functions.
• If you are not sure of exactly what the function or property syntax should look like, you can Option+click a similar built in method. For example, when I Option+clicked UIColor.greenColor I see the declaration is class func greenColor() -> UIColor. That gives me a good clue for how to set up my custom method.
• Apple Documentation for Extensions
• In Objective-C extensions are known as categories.

UIColor+util.swift

import UIKit




extension UIColor{




class func getCustomBlueColor() -> UIColor
{
return UIColor(red:0.043, green:0.576 ,blue:0.588 , alpha:1.00)
}


func getNameofColour() ->String
{
return "myOrange"
}


}

Usage :

NSLog("\(UIColor.getCustomBlueColor())")
let color=UIColor(red:0.043, green:0.576 ,blue:0.588 , alpha:1.00);
NSLog(color.getNameofColour())

I hope you see that what is difference . One of Function starting with class func another one starting only func . you can use which you like.

Swift 3.0 example:

extension UITextField
{


func useUnderline() {
let border = CALayer()
let borderWidth = CGFloat(1.0)
border.borderColor = UIColor.lightGray.cgColor
border.frame = CGRect(origin: CGPoint(x: 0,y :self.frame.size.height - borderWidth), size: CGSize(width: self.frame.size.width, height: self.frame.size.height))
border.borderWidth = borderWidth
self.layer.addSublayer(border)
self.layer.masksToBounds = true
}
}

Try this some new extension methods:

UIColor

extension UIColor{
//get new color from rgb value
class func RGB(_ red:CGFloat , andGreenColor green:CGFloat, andBlueColor blue:CGFloat, withAlpha alpha:CGFloat) -> UIColor
{
let color = UIColor(red: red/255.0, green: green/255.0, blue: blue/255.0, alpha: alpha)
return color
}
}


//return color from comma separated string of RGB paramater
convenience init(rgbString :String, alpha:CGFloat = 1.0){
let arrColor = rgbString.components(separatedBy: ",")
let red:CGFloat = CGFloat(NumberFormatter().number(from: arrColor[0])!)
let green:CGFloat = CGFloat(NumberFormatter().number(from: arrColor[1])!)
let blue:CGFloat = CGFloat(NumberFormatter().number(from: arrColor[2])!)
self.init(red: red/255.0, green: green/255.0, blue: blue/255.0, alpha: alpha)
}


//return color from hexadecimal value
//let color2 = UIColor(rgbHexaValue: 0xFFFFFFFF)
convenience init(rgbHexaValue: Int, alpha: CGFloat = 1.0) {
self.init(red:  CGFloat((rgbHexaValue >> 16) & 0xFF), green: CGFloat((rgbHexaValue >> 8) & 0xFF), blue: CGFloat(rgbHexaValue & 0xFF), alpha: alpha)
}
}

UITextField

extension UITextField{


//set cornerRadius
func cornerRadius(){
self.layoutIfNeeded()
self.layer.cornerRadius = self.frame.height / 2
self.clipsToBounds = true
}


//set bordercolor
func borderColor(){
self.layer.borderColor = TEXTFIELD_BORDER_COLOR.cgColor
self.layer.borderWidth = 1.0
}


//set borderWidth
func borderWidth(size:CGFloat){
self.layer.borderWidth = size
}


//check textfield is blank
func blank() -> Bool{
let strTrimmed = self.text!.trim()//get trimmed string
if(strTrimmed.characters.count == 0)//check textfield is nil or not ,if nil then return false
{
return true
}
return false
}


//set begginning space - left space
func setLeftPadding(paddingValue:CGFloat) {
let paddingView = UIView(frame: CGRect(x: 0, y: 0, width: paddingValue, height: self.frame.size.height))
self.leftViewMode = .always
self.leftView = paddingView
}


//set end of space
func setRightPadding(paddingValue:CGFloat){
let paddingView = UIView(frame: CGRect(x: (self.frame.size.width - paddingValue), y: 0, width: paddingValue, height: self.frame.size.height))
self.rightViewMode = .always
self.rightView = paddingView
}
}

UIFont

extension UIFont{
// Returns a scaled version of UIFont
func scaled(scaleFactor: CGFloat) -> UIFont {
let newDescriptor = fontDescriptor.withSize(fontDescriptor.pointSize * scaleFactor)
return UIFont(descriptor: newDescriptor, size: 0)
}
}

UIImage

public enum ImageFormat {
case PNG
case JPEG(CGFloat)
}




extension UIImage {
//convert image to base64 string
func toBase64() -> String {
var imageData: NSData
switch format {
case .PNG: imageData = UIImagePNGRepresentation(self)! as NSData
case .JPEG(let compression): imageData = UIImageJPEGRepresentation(self, compression)! as NSData
}
return imageData.base64EncodedString(options: .lineLength64Characters)
}


//convert string to image
class func base64ToImage(toImage strEncodeData: String) -> UIImage {
let dataDecoded  = NSData(base64Encoded: strEncodeData, options: NSData.Base64DecodingOptions.ignoreUnknownCharacters)!
let image = UIImage(data: dataDecoded as Data)
return image!
}


//Function for store file/Image into local directory. If image is already on the directory then first remove it and replace new image/File on that location
func storedFileIntoLocal(strImageName:String) -> String{
var strPath = ""
let documentDirectory1 = NSString.init(string: String.documentDirectory())
let imageName:String = strImageName + ".png"
let imagePath = documentDirectory1.appendingPathComponent(imageName)
strPath = imagePath
let fileManager = FileManager.default
let isExist = fileManager.fileExists(atPath: String.init(imagePath))
if(isExist == true)
{
do {
try fileManager.removeItem(atPath: imagePath as String)//removing file if exist
// print("Remove success")
} catch {
print(error)
}
}
let imageData:Data = UIImageJPEGRepresentation(self, 0.5)!
do {
try imageData.write(to: URL(fileURLWithPath: imagePath as String), options: .atomic)
} catch {
print(error)
strPath = "Failed to cache image data to disk"
return strPath
}


return strPath
}




//function for resize image
func resizeImage(targetSize: CGSize) -> UIImage {
let size = self.size


let widthRatio  = targetSize.width  / self.size.width
let heightRatio = targetSize.height / self.size.height


// Figure out what our orientation is, and use that to form the rectangle
var newSize: CGSize
if(widthRatio > heightRatio) {
newSize = CGSize(width: size.width * heightRatio, height: size.height * heightRatio)
} else {
//                        newSize = size
newSize = CGSize(width: size.width * widthRatio,  height: size.height * widthRatio)
}


// This is the rect that we've calculated out and this is what is actually used below
let rect = CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height)


// Actually do the resizing to the rect using the ImageContext stuff
UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)
self.draw(in: rect)
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()


return newImage!
}
}

Date

let YYYY_MM_DD_HH_MM_SS_zzzz = "yyyy-MM-dd HH:mm:ss +zzzz"
let YYYY_MM_DD_HH_MM_SS = "yyyy-MM-dd HH:mm:ss"
let DD_MM_YYYY = "dd-MM-yyyy"
let MM_DD_YYYY = "MM-dd-yyyy"
let YYYY_DD_MM = "yyyy-dd-MM"
let YYYY_MM_DD_T_HH_MM_SS = "yyyy-MM-dd'T'HH:mm:ss"


extension Date{


//convert string to date
static func convertStringToDate(strDate:String, dateFormate strFormate:String) -> Date{
let dateFormate = DateFormatter()
dateFormate.dateFormat = strFormate
dateFormate.timeZone = TimeZone.init(abbreviation: "UTC")
let dateResult:Date = dateFormate.date(from: strDate)!


return dateResult
}


//Function for old date format to new format from UTC to local
static func convertDateUTCToLocal(strDate:String, oldFormate strOldFormate:String, newFormate strNewFormate:String) -> String{
let dateFormatterUTC:DateFormatter = DateFormatter()
dateFormatterUTC.timeZone = NSTimeZone(abbreviation: "UTC") as TimeZone!//set UTC timeZone
dateFormatterUTC.dateFormat = strOldFormate //set old Format
if let oldDate:Date = dateFormatterUTC.date(from: strDate)  as Date?//convert date from input string
{
dateFormatterUTC.timeZone = NSTimeZone.local//set localtimeZone
dateFormatterUTC.dateFormat = strNewFormate //make new dateformatter for output format
if let strNewDate:String = dateFormatterUTC.string(from: oldDate as Date) as String?//convert dateInUTC into string and set into output
{
return strNewDate
}
return strDate
}
return strDate
}


//Convert without UTC to local
static func convertDateToLocal(strDate:String, oldFormate strOldFormate:String, newFormate strNewFormate:String) -> String{
let dateFormatterUTC:DateFormatter = DateFormatter()
//set local timeZone
dateFormatterUTC.dateFormat = strOldFormate //set old Format
if let oldDate:Date = dateFormatterUTC.date(from: strDate) as Date?//convert date from input string
{
dateFormatterUTC.timeZone = NSTimeZone.local
dateFormatterUTC.dateFormat = strNewFormate //make new dateformatter for output format
if let strNewDate = dateFormatterUTC.string(from: oldDate as Date) as String?//convert dateInUTC into string and set into output
{
return strNewDate
}
return strDate
}
return strDate
}


//Convert Date to String
func convertDateToString(strDateFormate:String) -> String{
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = strDateFormate
let strDate = dateFormatter.string(from: self)
//      dateFormatter = nil
return strDate
}




//Convert local to utc
static func convertLocalToUTC(strDate:String, oldFormate strOldFormate:String, newFormate strNewFormate:String) -> String{
let dateFormatterUTC:DateFormatter = DateFormatter()
dateFormatterUTC.timeZone = NSTimeZone.local as TimeZone!//set UTC timeZone
dateFormatterUTC.dateFormat = strOldFormate //set old Format
if let oldDate:Date = dateFormatterUTC.date(from: strDate)  as Date?//convert date from input string
{
dateFormatterUTC.timeZone = NSTimeZone.init(abbreviation: "UTC")! as TimeZone//set localtimeZone
dateFormatterUTC.dateFormat = strNewFormate //make new dateformatter for output format
if let strNewDate:String = dateFormatterUTC.string(from: oldDate as Date) as String?//convert dateInUTC into string and set into output
{
return strNewDate
}
return strDate
}
return strDate
}


//Comparison two date
static func compare(date:Date, compareDate:Date) -> String{
var strDateMessage:String = ""
let result:ComparisonResult = date.compare(compareDate)
switch result {
case .orderedAscending:
strDateMessage = "Future Date"
break
case .orderedDescending:
strDateMessage = "Past Date"
break
case .orderedSame:
strDateMessage = "Same Date"
break
default:
strDateMessage = "Error Date"
break
}
return strDateMessage
}
}

Calling this functions:

let color1 = UIColor.RGB(100.0, andGreenColor: 200.0, andBlueColor: 300.0, withAlpha: 1.0)
let color2 = UIColor.init(rgbHexaValue: 800000, alpha: 1.0)
let color3 = UIColor.init(rgbString: ("100.0,200.0,300.0", alpha: 1.0)


self.txtOutlet.cornerRadius()
self.txtOutlet.borderColor()
self.txtOutlet.setLeftPadding(paddingValue: 20.0)
self.txtOutlet.setRightPadding(paddingValue: 20.0)


let yourScaledFont = self.dependentView.font.scaled(scaleFactor: n as! CGFloat)
let base64String = (image?.toBase64(format: ImageFormat.PNG))!
let resultImage = UIImage.base64ToImage(toImage: base64String)
let path = yourImage.storedFileIntoLocal(strImageName: "imagename")

One of the best example of extension and convenience initializer :

 extension UIActivityIndicatorView {
convenience init(activityIndicatorStyle: UIActivityIndicatorViewStyle, color: UIColor, placeInTheCenterOf parentView: UIView) {
self.init(activityIndicatorStyle: activityIndicatorStyle)
center = parentView.center
self.color = color
parentView.addSubview(self)
}
}

You can use it in following ways :

1. Initialize activityIndicator

   let activityIndicator = UIActivityIndicatorView(activityIndicatorStyle: .whiteLarge, color: .gray,  placeInTheCenterOf: view)
   

2. Start animating activity indicator

   activityIndicator.startAnimating()
   

3. Stop animating activity indicator

   activityIndicator.stopAnimating()
   

Underline text in UITextField

Used in function ViewDidLoad()

firstNametext.underlined(0.5)

Extension

extension UITextField {


func underlined(_ size:Double){
let border = CALayer()
let width = CGFloat(size)
border.borderColor = UIColor.red.cgColor
border.frame = CGRect(x: 0, y: self.frame.size.height - width,
width:  self.frame.size.width, height: self.frame.size.height)
border.borderWidth = width
self.layer.addSublayer(border)
self.layer.masksToBounds = true }
}
}

If you like to use a colour with a given tint like used in brand manuals: Swift 4.2 + xcode 9.4.1.

extension UIColor {
func withTint(tint: CGFloat)->UIColor {


var tint = max(tint, 0)
tint = min(tint, 1)
/* Collect values of sender */
var r : CGFloat = 0
var g : CGFloat = 0
var b : CGFloat = 0
var a : CGFloat = 0
self.getRed(&r, green: &g, blue: &b, alpha: &a)


/* Calculate the tint */
r = r+(1-r)*(1-tint)
g = g+(1-g)*(1-tint)
b = b+(1-b)*(1-tint)
a = 1


return UIColor.init(red: r, green: g, blue: b, alpha: a)
}
}

In your code

let redWithTint = UIColor.red.withTint(tint: 0.4)

Here is an extension example of an eye catching animation effect that works with cells from UITableView. Each cell grows from a point source to normal size as you scroll a UITableView. Adjust the animation timing as desired.

Since each cell shows up with a little time stagger while scrolling, the effect ripples nicely! See this 15 second clip that showcases the effect : https://www.youtube.com/watch?v=BVeQpno56wU&feature=youtu.be

extension UITableViewCell {


func growCellDuringPresentation(thisCell : UITableViewCell) {


thisCell.transform = CGAffineTransform(scaleX: 0.01, y: 0.01)


UIView.animate(withDuration: TimeInterval(0.35), delay: 0.0, options: UIView.AnimationOptions.allowUserInteraction,   animations: {


thisCell.transform = CGAffineTransform(scaleX: 1, y: 1)


}, completion: nil)


}
}

To use the extension you make a call to it just before the cell is returned in cellForRowAt, like shown below :

cell.growCellDuringPresentation(thisCell: cell)
return cell

Note this same method works when returning cells for a collection view.

Here is an extension that works exactly the same, except that it rotates the cells during presentation :

extension UITableViewCell {


func rotateCellDuringPresentation(thisCell : UITableViewCell) {


thisCell.transform = CGAffineTransform(rotationAngle: .pi)


UIView.animate(withDuration: TimeInterval(0.35), delay: 0.0, options: UIView.AnimationOptions.allowUserInteraction,   animations: {


thisCell.transform = CGAffineTransform(rotationAngle: 0)


}, completion: nil)


}
}

It's called similarly :

cell.rotateCellDuringPresentation(thisCell: cell)
return cell

Here is an extension along the same lines that translates the cells in the X direction

extension UITableViewCell {


func translateCellDuringPresentation(thisCell : UITableViewCell) {


thisCell.layer.transform = CATransform3DMakeTranslation(-300, 0, 0)


UIView.animate(withDuration: TimeInterval(0.5), delay: 0.0, options: UIView.AnimationOptions.allowUserInteraction,   animations: {


thisCell.layer.transform = CATransform3DMakeTranslation(0, 0, 0)


}, completion: nil)


}
}

It's called similarly :

cell.translateCellDuringPresentation(thisCell: cell)
return cell