How to resize UIImageView based on UIImage's size/ratio in Swift 3?

Question

I have a UIImageView and the user is able to download UIImages in various formats. The issue is that I need the UIImageView to resize

Answer 1

The solution I used is based on olearyj234's solution, but makes having no image take up essentially no space (or more specifically the minimum iOS will accept). It also uses ceil to avoid problems which can occur with non-integer values when UIImageView's are embedded in things like scrolling cells.

class FixedWidthAspectFitImageView: UIImageView
{

    override var intrinsicContentSize: CGSize
    {
        // VALIDATE ELSE RETURN
        // frameSizeWidth
        let frameSizeWidth = self.frame.size.width

        // image
        // ⓘ In testing on iOS 12.1.4 heights of 1.0 and 0.5 were respected, but 0.1 and 0.0 led intrinsicContentSize to be ignored.
        guard let image = self.image else
        {
            return CGSize(width: frameSizeWidth, height: 1.0)
        }

        // MAIN
        let returnHeight = ceil(image.size.height * (frameSizeWidth / image.size.width))
        return CGSize(width: frameSizeWidth, height: returnHeight)
    }

}