title: How do I center and aspect fit an image in Swift 3?
body: <p>I have a project in Swift 3 that I am using a gradient on the view. I placed a image on the view, but it is under the gradient layer so I was going to draw the image programmatically instead of with the storyboard. I can't seem to figure out how to get the image to be centered and to aspect fit inside the bounds of the view.</p>
  
  <p>What I have...</p>
  
  <pre><code>//Gradient Background
  let gradientLayer = CAGradientLayer()
  gradientLayer.frame = self.view.frame
  gradientLayer.colors = [UIColor(red: 0/255, green: 147/255, blue: 255/255, alpha: 1.0).cgColor, UIColor(red: 162/255, green: 134/255, blue: 255/255, alpha: 1.0).cgColor]
  gradientLayer.locations = [0.0, 1.0]
  gradientLayer.startPoint = CGPoint(x: 0.0, y: 1.0)
  gradientLayer.endPoint = CGPoint(x: 1.0, y: 0.0)
  self.view.layer.addSublayer(gradientLayer)
  
  //Image
  let mainImage = UIImage(named:"WhiteLogoFront")
  var mainImageView = UIImageView(image:mainImage)
  self.view.addSubview(mainImageView)
  </code></pre>