How to set UIImageView with rounded corners for aspect fit mode

Swift 3 version of the helpful, accepted answer is over here!

extension UIImageView {
func roundCornersForAspectFit(radius: CGFloat)
{
    if let image = self.image {

        //calculate drawingRect
        let boundsScale = self.bounds.size.width / self.bounds.size.height
        let imageScale = image.size.width / image.size.height

        var drawingRect : CGRect = self.bounds

        if boundsScale > imageScale {
            drawingRect.size.width =  drawingRect.size.height * imageScale
            drawingRect.origin.x = (self.bounds.size.width - drawingRect.size.width) / 2
        }else {
            drawingRect.size.height = drawingRect.size.width / imageScale
            drawingRect.origin.y = (self.bounds.size.height - drawingRect.size.height) / 2
        }
        let path = UIBezierPath(roundedRect: drawingRect, cornerRadius: radius)
        let mask = CAShapeLayer()
        mask.path = path.cgPath
        self.layer.mask = mask
        }
    }
}

Use this extension to UIImageView:

extension UIImageView
{
    func roundCornersForAspectFit(radius: CGFloat)
    {
        if let image = self.image {

            //calculate drawingRect
            let boundsScale = self.bounds.size.width / self.bounds.size.height
            let imageScale = image.size.width / image.size.height

            var drawingRect: CGRect = self.bounds

            if boundsScale > imageScale {
                drawingRect.size.width =  drawingRect.size.height * imageScale
                drawingRect.origin.x = (self.bounds.size.width - drawingRect.size.width) / 2
            } else {
                drawingRect.size.height = drawingRect.size.width / imageScale
                drawingRect.origin.y = (self.bounds.size.height - drawingRect.size.height) / 2
            }
            let path = UIBezierPath(roundedRect: drawingRect, cornerRadius: radius)
            let mask = CAShapeLayer()
            mask.path = path.cgPath
            self.layer.mask = mask
        }
    }
}

Try this may help you:

import UIKit


class ViewController: UIViewController{

    @IBOutlet weak var myImageView: UIImageView!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        myImageView.contentMode = UIViewContentMode.ScaleAspectFit
        myImageView.clipsToBounds = true
        //myImageView.layer.cornerRadius = 10.0
        myImageView.layer.masksToBounds = true

        let simpleImage = UIImage(named:"ipad5_einladung.jpg")
        let corneredImage = generateRoundCornerImage(simpleImage!, radius: 10)

        //Set cornered Image
        myImageView.image = corneredImage;

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


    func generateRoundCornerImage(image : UIImage , radius : CGFloat) -> UIImage {

        let imageLayer = CALayer()
        imageLayer.frame = CGRectMake(0, 0, image.size.width, image.size.height)
        imageLayer.contents = image.CGImage
        imageLayer.masksToBounds = true
        imageLayer.cornerRadius = radius

        UIGraphicsBeginImageContext(image.size)
        imageLayer.renderInContext(UIGraphicsGetCurrentContext())
        let roundedImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return roundedImage
    }

}