Swift Cheat Sheet to save time.

Swift3.1 CheatSheet Plus

/*
 * Author  : Jeevan Rao
 * Date    : 13/0/2017 
 * Swift   : V3.1
 */
 
/* UI + UX Tricks */
//Selection style of table view cell (other than Default grey / Blue/ none)
        let selectionColorView = UIView()
        selectionColorView.backgroundColor = UIColor.blue
        cell.selectedBackgroundView = selectionColorView
  
//UISeachBar Cancel button color
UIBarButtonItem.appearance(whenContainedInInstancesOf:[UISearchBar.self]).tintColor = UIColor.white

//Slowdown UI Updates
    func delay(_ delay:Double, closure:@escaping ()->()) {
        let when = DispatchTime.now() + delay
        DispatchQueue.main.asyncAfter(deadline: when, execute: closure)
    }
    
/* Extensions */

//Bottom border for text field
extension UITextField
{
    //Bottom line/border for UITextfield
    func setBottomBorderColor(_ color:UIColor)
    {
        self.borderStyle = .none;
        let border = CALayer()
        let width = CGFloat(1.0)
        border.borderColor = color.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
    }
}

//Shadow - card effect for UIView
extension UIView {
    func addDropShadowToView(){
        self.layer.masksToBounds = false
        self.layer.shadowColor = UIColor.gray.cgColor;
        self.layer.shadowOffset = CGSize(width:2.0, height:2.0)
        self.layer.shadowOpacity = 0.75
    }
}

// Make ‘String’ to return its Length
extension String {
   var length: Int {
       return (self as NSString).length
   }
}

//Will return NSAttributedString from HTML String
extension String{
    func convertHtml() -> NSAttributedString{
        guard let data = data(using: .utf8) else { return NSAttributedString() }
        do{
            return try NSAttributedString(data: data, options: [NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType, NSCharacterEncodingDocumentAttribute: String.Encoding.utf8.rawValue], documentAttributes: nil)
        }catch{
            return NSAttributedString()
        }
    }
}
myLabel.attributedText = "<b>Bolded</b>".convertHtml() //Example

//Gives array of unique elements from given array
extension Sequence where Iterator.Element: Hashable {
    func unique() -> [Iterator.Element] {
        var seen: [Iterator.Element: Bool] = [:]
        return self.filter { seen.updateValue(true, forKey: $0) == nil }
    }
}


/* Misc */

//Calculates execution time of block of code.
            let info = ProcessInfo.processInfo
            let begin = info.systemUptime
            //Code Stuff
            let diff = (info.systemUptime - begin)


//List all the installed Fonts 

        for fontFamilyName in UIFont.familyNames{
            for fontName in UIFont.fontNames(forFamilyName: fontFamilyName){
                print("Family: \(fontFamilyName)     Font: \(fontName)")
            }
        }
        
    
//RESET User Defaults (all keys)
        let domain = Bundle.main.bundleIdentifier!
        UserDefaults.standard.removePersistentDomain(forName: domain)
        UserDefaults.standard.synchronize()

//Generate UIImage object from UIView
   func generateImage(for view: UIView) -> UIImage? {
        defer {
            UIGraphicsEndImageContext()
        }
        UIGraphicsBeginImageContextWithOptions(view.bounds.size, false, UIScreen.main.scale)
        if let context = UIGraphicsGetCurrentContext() {
            view.layer.render(in: context)
            return UIGraphicsGetImageFromCurrentImageContext()
        }
        return nil
    }
    
    //:usage 
      var iconWithTextImage: UIImage {
        let containerView = UIView.init(frame: CGRect(x: 0, y: 0, width: 30, height: 30))
        let icon = UIImageView.init(frame: CGRect(x: 0, y: 0, width: 30, height: 30))
        icon.image = UIImage.init(named: "shirt.png")
        icon.contentMode = .scaleAspectFit
        containerView.addSubview(icon)
        return generateImage(for: containerView) ?? UIImage()
    }
    
//CLOSURE Callback Example 
//Closure Callback : 
public typealias Closure = () -> Void

//Definition
public var exitFromTap  = Closure?({})

//Declaration in somewhere needs a callback.
 exitFromTap?()

//Usage
yourClass.exitFromTap = {    print(“Good Bye”)     }

/// Returns the element at the specified index iff it is within bounds, otherwise nil.
extension Collection {
    subscript (safe index: Index) -> Element? {
        return indices.contains(index) ? self[index] : nil
    }
}


let sample = ["BMW", "Audi", "Tesla", "Fiat"]
sample[safe : 0] //Prints "BMW"
sample[safe : 4] //Prints 'nil'

Swift4 Cheetsheet Plus

/// String extension : replacement for' subString:'
   extension String {
     func slice(from: String, to: String) -> String? {
        
        let fromIndex = self.index(self.index(of: from)!, offsetBy: 1)
        let toIndex = self.index(self.index(of: to)!, offsetBy: -1)
        
        return String(self[fromIndex...toIndex])
     }
   }
 //Usage : "Date(1511508780012+0530)".slice(from: "(", to: "+")
 

//Core Data - Easy & Clean way to get NSManagedContext  

   public static func getContext() -> NSManagedObjectContext {
        let appDelegate = UIApplication.shared.delegate as! AppDelegate
        return appDelegate.persistentContainer.viewContext
    }

//Limit characters in text filed
    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        
        let currentCharacterCount = textField.text?.count ?? 0
        if (range.length + range.location > currentCharacterCount){
            return false
        }
        let newLength = currentCharacterCount + string.count - range.length
        return newLength <= Constants.nameCharLimit
    }

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1. Any UIViewController (including UINavigationControllers as UINavigationControllers are a type of UIViewControllers) presented modally must be dismissed.

2. Since UINavigationControllers hold UIViewControllers in their stack, they can present UIViewControllers both modally and via a push. When navigating away from any pushed UIViewControllers, UINavigationControllers must pop the UIViewController.

3. Though it is possible to present UIViewControllers both modally and via a push, UIViewControllers can only present other UIViewControllers. Therefore, UIViewControllers can only be dismissed (unless they are inside a UINavigationController stack and the UINavigationController is handling the pop — see lesson #2). This is why it is not possible to call popViewController on a UIViewController.

4. PresentingViewController is a property provided by Apple that is available on both UIViewControllers and UINavigationControllers. Calling presentingViewController.dismiss(animated:completion) will dismiss everything presented by the parentViewController. The parentViewController is the UIViewController that presented the current UIViewController. So, if you have a UINavigationController with 3 UIViewControllers within its stack, calling presentingViewController.dismiss(animated:completion) will dismiss both the UINavigationController and the 3 UIViewControllers held within its stack.

5.Similarly, Apple also provides another property on UIViewControllers and UINavigationControllers — presentedViewController. Calling presentedViewController.dismiss(animated:completion) will dismiss the childViewController. The childViewController is the current UIViewController that is being presented.