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

I modified @user8969729 's solution to replace the "fixed" width/height with "max", thus more like @JoshuaHart's solution. Handle the maxWidth == 0 / maxHeight == 0 case as you wish, since I always had both set I just quickly ignored that case.

public class AdjustsViewBoundsImageView: UIImageView {
   
   /// The maximum width that you want this imageView to grow to.
   @objc dynamic var maxWidth: CGFloat = 0 {
      didSet {
         invalidateIntrinsicContentSize()
      }
   }
   
   /// The maximum height that you want this imageView to grow to.
   @objc dynamic var maxHeight: CGFloat = 0 {
      didSet {
         invalidateIntrinsicContentSize()
      }
   }
   
   private var maxAspectRatio: CGFloat { return maxWidth / maxHeight }
   
   override public var intrinsicContentSize: CGSize {
      guard let classImage = self.image else { return super.intrinsicContentSize }
      if maxHeight == 0 || maxWidth == 0 {
         return super.intrinsicContentSize
      }
      
      let imageWidth = classImage.size.width
      let imageHeight = classImage.size.height
      let aspectRatio = imageWidth / imageHeight
      
      // Width is greater than height, return max width image and new height.
      if imageWidth > imageHeight {
         let newHeight = maxWidth/aspectRatio
         return CGSize(width: maxWidth, height: newHeight)
      }
      
      // Height is greater than width, return max height and new width.
      if imageHeight > imageWidth {
         // If the aspect ratio is larger than our max ratio, then using max width
         // will be hit before max height.
         if aspectRatio > maxAspectRatio {
            let newHeight = maxWidth/aspectRatio
            return CGSize(width: maxWidth, height: newHeight)
         }
         let newWidth = maxHeight * aspectRatio
         return CGSize(width: newWidth, height: maxHeight)
      }
      
      // Square image, return the lesser of max width and height.
      let squareMinimumValue = min(maxWidth, maxHeight)
      return CGSize(width: squareMinimumValue, height: squareMinimumValue)
   }
}