add Shadow on UIView using swift 3

CODE SNIPPET:

extension UIView {

  // OUTPUT 1
  func dropShadow(scale: Bool = true) {
    layer.masksToBounds = false
    layer.shadowColor = UIColor.black.cgColor
    layer.shadowOpacity = 0.5
    layer.shadowOffset = CGSize(width: -1, height: 1)
    layer.shadowRadius = 1

    layer.shadowPath = UIBezierPath(rect: bounds).cgPath
    layer.shouldRasterize = true
    layer.rasterizationScale = scale ? UIScreen.main.scale : 1
  }

  // OUTPUT 2
  func dropShadow(color: UIColor, opacity: Float = 0.5, offSet: CGSize, radius: CGFloat = 1, scale: Bool = true) {
    layer.masksToBounds = false
    layer.shadowColor = color.cgColor
    layer.shadowOpacity = opacity
    layer.shadowOffset = offSet
    layer.shadowRadius = radius

    layer.shadowPath = UIBezierPath(rect: self.bounds).cgPath
    layer.shouldRasterize = true
    layer.rasterizationScale = scale ? UIScreen.main.scale : 1
  }
}

NOTE: If you don’t pass any parameter to that function, then the scale argument will be true by default. You can define a default value for any parameter in a function by assigning a value to the parameter after that parameter’s type. If a default value is defined, you can omit that parameter when calling the function.

OUTPUT 1:

shadowView.dropShadow()

OUTPUT 2:

shadowView.dropShadow(color: .red, opacity: 1, offSet: CGSize(width: -1, height: 1), radius: 3, scale: true)

layer.shouldRasterize = true will make the shadow static and cause a shadow for the initial state of the UIView. So I would recommend not to use layer.shouldRasterize = true in dynamic layouts like view inside a UITableViewCell.