How_to_create_a_stored_property_in_an_swift_extension.swift

extension UITextField {
    
    // OPTION - 1
    struct Instance {
        static var floating: Bool = false
    }
    
    
    var floating: Bool{
        set{
            Instance.floating = newValue
            initializePlaceholder()
        }
        
        get{
            return Instance.floating
        }
    }

    

    // OPTION - 2
    struct AssociatedKeys {
        static var placeholderColor: String = "placeholderColor"
    }
    
    var  placeholderColor: UIColor? {
        set {
            objc_setAssociatedObject(self, &AssociatedKeys.placeholderColor, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)
            updatePlaceholderAppearance()
        }
        
        get {
            guard let value = objc_getAssociatedObject(self, &AssociatedKeys.placeholderColor) as? UIColor else { return nil }
            return value
        }
    }
    
    
    // MARK: - Helper functions
    func initializePlaceholder(){
        guard floating == true else {
            return
        }
        if let _ = placeholderLabel(){
            return
        }
        
        addObserver(self, forKeyPath: "placeholder", options: NSKeyValueObservingOptions.new, context: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(handleKeyboard), name: NSNotification.Name.UIKeyboardWillHide, object: nil)

        
        let label = UILabel(frame: CGRect(origin: CGPoint(x: 5, y: 0), size: bounds.size))
        label.text = placeholder
        label.font = font
        addSubview(label)
        placeholder = ""
        let gesture = UITapGestureRecognizer(target: self, action: #selector(animatePlaceholderLabel))
        label.isUserInteractionEnabled = true
        label.tag = 765678
        label.addGestureRecognizer(gesture)
    }
    
    
    func placeholderLabel() ->UILabel? {
        if let label = viewWithTag(765678) as? UILabel{
            return label
        }
        return nil
    }
    
    fileprivate  func fontSize() ->CGFloat? {
        return font?.pointSize
    }
    
    fileprivate  func fontName() ->String? {
        return font?.familyName
    }
    
    fileprivate func updatePlaceholder() {
        guard let label = placeholderLabel() else { return }
        label.text = placeholder
        attributedPlaceholder = NSAttributedString(string: placeholder!, attributes: [NSAttributedStringKey.foregroundColor : UIColor.clear])
    }
    
    fileprivate func updatePlaceholderAppearance() {
        guard let label = placeholderLabel() else { return }
        label.font = self.font
        label.textColor = placeholderColor
    }
    
    
    @objc private func animatePlaceholderLabel() {
        becomeFirstResponder()
        guard let label = placeholderLabel() else { return }
        UIView.animate(withDuration: 0.5, animations: {
            label.frame = CGRect(origin: CGPoint(x: 5, y: -(self.bounds.size.height * 0.5 + 3)), size: CGSize(width: self.bounds.size.width * 0.5, height: self.bounds.size.height * 0.5))
        })
    }
    
    @objc func handleKeyboard() {
        if let count = text?.count, count > 0 { return }
        guard let label = placeholderLabel() else { return }
        UIView.animate(withDuration: 0.3, animations: {
            label.frame = CGRect(origin: CGPoint(x: 5, y: 0), size: self.bounds.size)
            if let name = self.fontName(), let size = self.fontSize(){
                label.font = UIFont(name: name, size: size)
            }
        })
    }
    

    
    open override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        if let path = keyPath, path == "placeholder" {
            updatePlaceholder()
        }
    }
    
    
    /*
    // Only override draw() if you perform custom drawing.
    // An empty implementation adversely affects performance during animation.
    override func draw(_ rect: CGRect) {
        // Drawing code
    }
    */

}