A drop down textfield with RxSwift

DropdownTextField.swift

import UIKit
import RxSwift
import RxCocoa

final class DropdownTextField: CustomTextField, UIPickerViewDataSource, UIPickerViewDelegate {

    var onDoneClicked: BehaviorRelay<Void?> = BehaviorRelay(value: nil)

    var source: [String] = []

    let selectedValue: BehaviorRelay<String?> = BehaviorRelay(value: nil)

    let hasValidData = BehaviorRelay(value: false)
    let hasValueSelected = BehaviorRelay(value: false)

    private let picker = UIPickerView()

    private let disposeBag = DisposeBag()

    override func setup() {
        super.setup()
        setupViewHierarchy()
        setupBehavior()
    }

    private let iconImageView: UIImageView = {
        let imageView = UIImageView()
        imageView.image = Asset.Common.chevronDown.image
        imageView.contentMode = .scaleAspectFit
        return imageView.layoutable()
    }()

    private let activityIndicator = UIActivityIndicatorView(style: .gray).layoutable()

    func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
        if !source.isEmpty {
            text = source[row]
            hasValueSelected.accept(true)
            selectedValue.accept(text)
        }
    }

    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return source[row]
    }

    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }

    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return source.count
    }

    private func setupViewHierarchy() {
        addSubviews([iconImageView, activityIndicator])
        iconImageView.constraintCenterToSuperview(axis: [.vertical], withConstant: .zero)
        iconImageView.constraintToConstant(CGSize(width: 13, height: 13))
        iconImageView.rightAnchor.constraint(equalTo: rightAnchor, constant: -18).isActive = true
        activityIndicator.constraintCenter(to: iconImageView)
    }

    private func setupBehavior() {
        picker.delegate = self
        inputView = picker

        let flexBarButton = UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: nil, action: nil)
        let doneBarButton = UIBarButtonItem(barButtonSystemItem: .done, target: self, action: #selector(dismissInputView))
        keyboardToolbar.items = [doneBarButton, flexBarButton]
        self.inputAccessoryView = keyboardToolbar

        hasValidData
            .observeOn(MainScheduler.instance)
            .subscribe(onNext: { [weak self] hasData in
                self?.iconImageView.isHidden = !hasData
                self?.activityIndicator.isHidden = hasData
                hasData ? self?.activityIndicator.stopAnimating() : self?.activityIndicator.startAnimating()
            })
            .disposed(by: disposeBag)
    }

    @objc private func dismissInputView() {
        self.onDoneClicked.accept(())
        self.endEditing(true)
    }
}

Thanks for sharing!
Do you mind to tell what's in CustomTextField please?

Welcome!

So CustomTextField can be any of your custom textfields, or default UITextField in my case it's the following.

class CustomTextField: UITextField {
	
	var textInset: UIEdgeInsets { .zero }
	
	var textPlaceholderColor: UIColor = .textPlaceholderColor
	
	override var placeholder: String? {
		didSet {
			attributedPlaceholder = NSAttributedString(string: placeholder ?? "", attributes:  [NSAttributedString.Key.foregroundColor: textPlaceholderColor, NSAttributedString.Key.font: UIFont.medium(ofSize: 16)])
		}
	}
	
	override init(frame: CGRect) {
		super.init(frame: frame)
 		setup()
	}
	
	required init?(coder: NSCoder) {
		fatalError()
	}
	
	override func textRect(forBounds bounds: CGRect) -> CGRect {
		return bounds.inset(by: textInset)
	}
	
	override func editingRect(forBounds bounds: CGRect) -> CGRect {
		return bounds.inset(by: textInset)
	}
	
	func setup() {
		autocorrectionType = .no
		font = .medium(ofSize: 18)
	}
}

Appreciated once again!