ResizingTableView.swift

class ResizingTableView: UITableView {
    
    private var heightConstraint: NSLayoutConstraint?
    
    override init(frame: CGRect, style: UITableViewStyle) {
        super.init(frame: frame, style: style)
        
        self.addObserver(self, forKeyPath: #keyPath(contentSize), options: .new, context: nil)
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    deinit {
        self.removeObserver(self, forKeyPath: #keyPath(contentSize), context: nil)
    }
    
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        if keyPath == #keyPath(contentSize) {
            _ = heightConstraint.map { NSLayoutConstraint.deactivate([$0]) }
            heightConstraint = self.heightAnchor.constraint(equalToConstant: contentSize.height)
            _ = heightConstraint.map { NSLayoutConstraint.activate([$0]) }
        }
    }
    
}