RxSwift Observable on iOS keyboard height. Updated from original. Changelog below.

keyboardHeightObservable.swift

import RxSwift // Version 3.2.0
import RxCocoa // Version 3.2.0

typealias KeyboardHeightInfo = (CGFloat, TimeInterval)

func keyboardHeight() -> Driver<KeyboardHeightInfo> {
  return Observable
    .from([
      NotificationCenter.default.rx.notification(NSNotification.Name.UIKeyboardWillShow)
        .map { notification -> KeyboardHeightInfo in
          let userInfo = notification.userInfo
          let value = (userInfo?[UIKeyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue.height ?? 0
          let animationDuration = userInfo?[UIKeyboardAnimationDurationUserInfoKey] as? TimeInterval ?? 0
          return (value, animationDuration)
      },
      NotificationCenter.default.rx.notification(NSNotification.Name.UIKeyboardWillHide)
        .map { notification -> KeyboardHeightInfo in
          let userInfo = notification.userInfo
          let animationDuration = userInfo?[UIKeyboardAnimationDurationUserInfoKey] as? TimeInterval ?? 0
          return (0, animationDuration)
      }
      ])
    .merge()
    .asDriver(onErrorDriveWith: Driver.never())
}

usage.swift

import RxSwift // Version 3.2.0
import RxCocoa // Version 3.2.0
import UIKit

class MyView: UIView {
    fileprivate disposeBag = DisposeBag()
  
    // Note: tableView and constraints are omitted here.
    
    private lazy var resultTableViewBottomConstraint: NSLayoutConstraint = {
        return NSLayoutConstraint(item: view, attribute: .bottom, relatedBy: .equal,
                                  toItem: tableView, attribute: .bottom, multiplier: 1.0, constant: 0)
    }()
    
    init() {
        super.init(frame: CGRect.zero)
    
    keyboardHeight()
        .drive(onNext: { [unowned self] (value, animationDuration) in
            self.resultTableViewBottomConstraint.constant = value
            UIView.animate(withDuration: animationDuration, animations: { () -> Void in
                self.view.layoutIfNeeded()
            })
        })
    }
    
    required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented") }
}

Update from original:

• Change to return Driver instead.
• Refactor keyboard height parsing and add animation duration.
• Use UIKeyboardFrameEndUserInfoKey instead of UIKeyboardFrameBeginUserInfoKey.
• Update usage example with change animation.