RxSwift Observable on iOS keyboard height

keyboardHeightObservable.swift

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

func keyboardHeight() -> Observable<CGFloat> {
    return Observable
            .from([
                    NotificationCenter.default.rx.notification(NSNotification.Name.UIKeyboardWillShow)
                            .map { notification -> CGFloat in
                                (notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue.height ?? 0
                            },
                    NotificationCenter.default.rx.notification(NSNotification.Name.UIKeyboardWillHide)
                            .map { _ -> CGFloat in
                                0
                            }
            ])
            .merge()
}

usage.swift

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

class MyView: UIView {
    fileprivate disposeBag = DisposeBag()
  
    init() {
        super.init(frame: CGRect.zero)
    
        keyboardHeight()
            .observeOn(MainScheduler.instance)
            .subscribe(onNext: { (keyboardHeight): CGFloat in
                // adjust other views with keyboardHeight                    
            })
            .addDisposableTo(disposeBag)
    }
    
    required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented") }
}

This worked well for me, but I had to replace UIKeyboardFrameBeginUserInfoKey with UIKeyboardFrameEndUserInfoKey to get the correct height value.