This extension is to get image's aspectFill frame

Extension+UIImageView.swift

extension UIImageView {
    
    var getImageAspectFillFrame: CGRect? {
        guard let image = image, frame != .zero else { return nil }
        let imageSize = image.size
        if imageSize.width > imageSize.height { // landscape
            return calcMaxWidth(imageSize, frame.size)
            
        } else if imageSize.height > imageSize.width { // portrait
            return calcMaxHeight(imageSize, frame.size)
            
        } else { // square
            if frame.width > frame.height {
                return calcMaxHeight(imageSize, frame.size)
                
            } else if frame.height > frame.width {
                return calcMaxWidth(imageSize, frame.size)
                
            } else {
                return CGRect(origin: .zero, size: frame.size)
            }
        }
    }
    
    func calcMaxWidth(_ imageSize: CGSize, _ frameSize: CGSize) -> CGRect {
        var height = frameSize.height
        var width = imageSize.width * height / imageSize.height
        if width.isNaN {
            width = 0.0
        } else if width < frameSize.width {
            width = frameSize.width
            height = imageSize.height * width / imageSize.width
        }
        let pos = CGPoint(x: (frameSize.width/2) - (width/2), y: (frameSize.height/2) - (height/2))
        return CGRect(origin: pos, size: CGSize(width: width, height: height))
    }
    
    func calcMaxHeight(_ imageSize: CGSize, _ frameSize: CGSize) -> CGRect {
        var width = frameSize.width
        var height = imageSize.height * width / imageSize.width
        if height.isNaN {
            height = 0.0
        } else if height < frameSize.height {
            height = frameSize.height
            width = imageSize.width * height / imageSize.height
        }
        let pos = CGPoint(x: (frameSize.width/2) - (width/2), y: (frameSize.height/2) - (height/2))
        return CGRect(origin: pos, size: CGSize(width: width, height: height))
    }
    
}