FloatingView.swift

import UIKit

class FloatingView: UIView {

    var keyboardSize: CGFloat = 0

    open var height: CGFloat = 56 {
        didSet {
            self.setNeedsDisplay()
        }
    }

    open var paddingY: CGFloat = 0 {
        didSet {
            self.setNeedsDisplay()
        }
    }

    /**
     Initialize with custom frame.
     */
    public override init(frame: CGRect) {
        super.init(frame: frame)
        height = frame.size.height
        backgroundColor = UIColor.clear
        layer.zPosition = 1000
        setObserver()
    }

    /**
     Initialize from storyboard.
     */
    public required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    // MARK: - Method

    public func setFrameToBottom() {
        if superview == nil {
            frame = CGRect(
                x: 0,
                y: (UIScreen.main.bounds.size.height - height - keyboardSize) - paddingY,
                width: UIScreen.main.bounds.size.width,
                height: height
            )
        } else {
            if let scrollView = superview as? UIScrollView {
                frame = CGRect(
                    x: scrollView.contentOffset.x,
                    y: (superview!.bounds.size.height - height - keyboardSize - paddingY) + scrollView.contentOffset.y,
                    width: superview!.bounds.size.width,
                    height: height
                )
            } else {
                frame = CGRect(
                    x: 0,
                    y: (superview!.bounds.size.height - height - keyboardSize) - paddingY,
                    width: superview!.bounds.size.width,
                    height: height
                )
            }
        }
    }

    fileprivate func setObserver() {
        NotificationCenter.default.addObserver(self, selector: #selector(deviceOrientationDidChange(_:)), name: NSNotification.Name.UIDeviceOrientationDidChange, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillShow(_:)), name:NSNotification.Name.UIKeyboardWillShow, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillHide(_:)), name:NSNotification.Name.UIKeyboardWillHide, object: nil)
    }

    deinit {
        NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIDeviceOrientationDidChange, object: nil)
        NotificationCenter.default.removeObserver(self, name:NSNotification.Name.UIKeyboardWillShow, object: nil)
        NotificationCenter.default.removeObserver(self, name:NSNotification.Name.UIKeyboardWillHide, object: nil)
    }

    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        setFrameToBottom()
    }

    override func willMove(toSuperview newSuperview: UIView?) {
        superview?.removeObserver(self, forKeyPath: "frame")
        superview?.removeObserver(self, forKeyPath: "contentOffset")
        super.willMove(toSuperview: newSuperview)
    }

    override func didMoveToSuperview() {
        super.didMoveToSuperview()
        superview?.addObserver(self, forKeyPath: "frame", options: [], context: nil)
        superview?.addObserver(self, forKeyPath: "contentOffset", options: .new, context:nil)
    }

    internal func deviceOrientationDidChange(_ notification: Notification) {
        guard let keyboardSize: CGFloat = (notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue.size.height else {
            self.keyboardSize = 0
            return
        }

        self.keyboardSize = keyboardSize

        setFrameToBottom()
    }

    internal func keyboardWillShow(_ notification: Notification) {
        guard let keyboardSize: CGFloat = (notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue.size.height else {
            self.keyboardSize = 0
            return
        }

        self.keyboardSize = keyboardSize

        UIView.animate(withDuration: 0.2, delay: 0, options: UIViewAnimationOptions(), animations: {
            self.setFrameToBottom()
        }, completion: nil)
    }

    internal func keyboardWillHide(_ notification: Notification) {
        self.keyboardSize = 0

        UIView.animate(withDuration: 0.2, delay: 0, options: UIViewAnimationOptions(), animations: {
            self.setFrameToBottom()
        }, completion: nil)
    }
}