ImageViewFrameSize-example.swift

class ViewController: UIViewController {

    var image: UIImage!
    var imageView: UIImageView!

    override func viewDidLoad() {
        super.viewDidLoad()
        let avatarData = NSData(contentsOfURL: NSURL(string: "https://www.gravatar.com/avatar/7d7c8bd1f797a0e9b474e52c3968cbde?s=48&d=identicon&r=PG")!)

        let landscapeData = NSData(contentsOfURL: NSURL(string: "https://upload.wikimedia.org/wikipedia/commons/e/e4/Stourhead_garden.jpg")!)

        let portraitData = NSData(contentsOfURL: NSURL(string: "http://1.bp.blogspot.com/-hNC-oT6f-fY/TeXxO26yjvI/AAAAAAAAAOY/qfkOqdKkBi8/s1600/platon-photographer-putin-man-of-the-year-portrait.jpg")!)

        image = UIImage(data: landscapeData!)
        imageView = UIImageView(image: image!)

        view.backgroundColor = .whiteColor()
        view.addSubview(imageView)

        if image.size.height > image.size.width {
            // Portrait
            print("Portrait")
        }
        else {
            // Landscape
            print("Landscape")
        }

        print("mainScreen().bounds.width", UIScreen.mainScreen().bounds.width)
        let finalHeight = UIScreen.mainScreen().bounds.width * image.size.height / image.size.width
        print("finalHeight", finalHeight)

        imageView.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activateConstraints([
            imageView.topAnchor.constraintEqualToAnchor(view.topAnchor, constant: 5),
            imageView.leadingAnchor.constraintEqualToAnchor(view.leadingAnchor, constant: 5),
            imageView.trailingAnchor.constraintEqualToAnchor(view.trailingAnchor, constant: -5),
            imageView.heightAnchor.constraintEqualToConstant(finalHeight),
        ])

        imageView.backgroundColor = .blueColor()
        imageView.contentMode = .ScaleAspectFit
        imageView.clipsToBounds = true

        print("imageView.frame", imageView.frame)
        print("image.size", image.size)

        // ---------
        let currentRunloop = CFRunLoopGetCurrent()
        print("Before delay")
        delay(3.0) {
            print("Delay execution")
            CFRunLoopPerformBlock(currentRunloop, NSRunLoopCommonModes) {
                print("Perform block")
            }
            CFRunLoopWakeUp(currentRunloop)
        }
        print("After delay")
    }

    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)
        print("imageView.frame", imageView.frame)
        print("image.size", image.size)
    }

}

public func delay(seconds: NSTimeInterval, closure: ()->()) {
    dispatch_after(
        dispatch_time(
            DISPATCH_TIME_NOW,
            Int64(seconds * Double(NSEC_PER_SEC))
        ),
        dispatch_get_main_queue(),
        closure
    )
}