Most commonly used methods.

CONFIG.swift

// Best way to dismiss the keyboard
func resignKeyboard(){
    UIApplication.shared.sendAction(#selector(UIResponder.resignFirstResponder), to:nil, from:nil, for:nil)
    // Visit this link: http://roadfiresoftware.com/2015/01/the-easy-way-to-dismiss-the-ios-keyboard/
}

// Used to set the status bar background color.
func setStatusBarBackgroundColor(color: UIColor) {
    // Beware that this method uses the private API, your app might bet rejected from the app store.
    guard let statusBar = UIApplication.shared.value(forKeyPath: "statusBarWindow.statusBar") as? UIView else { return }
    statusBar.backgroundColor = color
}

// toggle the shadow below the navigation bar.
func showShadownBelow(_ navigationBar: UINavigationBar, hide: Bool) {
    navigationBar.layer.shadowColor = UIColor.black.cgColor
    navigationBar.layer.shadowOffset = hide ? CGSize(width: 0.0, height: 2.0) : CGSize(width: 0.0, height: 2.0)
    navigationBar.layer.shadowRadius = hide ? 0.0 : 4.0
    navigationBar.layer.shadowOpacity = hide ? 0.0 : 0.5
    navigationBar.layer.masksToBounds = false
}

// toggle the line which is present below navigation bar.
func toggleLineBelow(_ navigationBar: UINavigationBar, hide: Bool) {
    navigationBar.shadowImage.alpha = hide ? 0.0 : 1.0
}

// This will print all the fonts that are available for the projetct including that you have added in the xcode.
let fontFamilyNames = UIFont.familyNames
  for familyName in fontFamilyNames {
  print("------------------------------")
  print("Font Family Name = [\(familyName)]")
  let names = UIFont.fontNames(forFamilyName: familyName)
  print("Font Names = [\(names)]")
}

func degreesToRadians(degrees: CGFloat) -> CGFloat {
    return degrees * CGFloat(M_PI) / 180
}

func radiansToDegress(radians: CGFloat) -> CGFloat {
    return radians * 180 / CGFloat(M_PI)
}

// Load image async and cache
// var imageCache = NSCache<AnyObject, AnyObject>()
func setImage(with url: URL, imageView: UIImageView, placeholderImage: UIImage, imageCache: NSCache<AnyObject, AnyObject>?, completion: @escaping (Bool)->()) {
    imageView.image = placeholderImage
    if let image = imageCache?.object(forKey: url as AnyObject) as? UIImage {
        // If image is found, assign the image and return
        imageView.image = image
        completion(true)
        return
    }
    
    // Image not found so download the image.
    URLSession.shared.dataTask(with: url) { (data, response, error) in
        if error != nil && data != nil {
            print(error!.localizedDescription)
            completion(false)
            return
        }
            
        DispatchQueue.main.async {
            let imageToCache = UIImage(data: data!)
            self.imageCache?.setObject(imageToCache!, forKey: url as AnyObject)
            imageView.image = imageToCache
            completion(true)
        }
    }.resume()
}

*------------------------- Way to cache profile image. -------------------------*
// Since UIImage doesn't confirm to NSCoding protocol so we have to save UIImage as Data.
var profilePictureCache = settingDefaults.value(forKey: "profilePictureCache") as? Data {
    didSet {
        settingDefaults.setValue(profilePictureCache, forKey: "profilePictureCache")
    }
}

func showProfilePicture(imageView: UIImageView, url: URL) {
    imageView.image = #imageLiteral(resourceName: "ProfilePlaceholder-1")
    
    if let image = profilePictureCache {
        imageView.image = UIImage(data: image)
        return
    }
    
    URLSession.shared.dataTask(with: url) { (data, response, error) in
        if error != nil && data != nil {
            print(error!.localizedDescription)
            return
        }
        
        DispatchQueue.main.async {
            profilePictureCache = data!
            imageView.image = UIImage(data: data!)
        }
    }.resume()
}