IndicatorButton.swift

import UIKit

class IndicatorButton: UIButton {
    
    private var indicatorView: UIActivityIndicatorView = {
        let aiv = UIActivityIndicatorView(style: .white)
        aiv.hidesWhenStopped = true
        aiv.translatesAutoresizingMaskIntoConstraints = false
        aiv.isUserInteractionEnabled = false
        return aiv
    }()
    
    var isAnimating: Bool {
        return indicatorView.isAnimating
    }
    
    private var previousText: String?
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        setup()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setup()
    }
    
    func setup() {
        self.layer.shadowColor = UIColor.clear.cgColor
        self.previousText = currentTitle
        self.addSubview(indicatorView)
        indicatorView.centerXAnchor.constraint(equalTo: self.centerXAnchor).isActive = true
        indicatorView.centerYAnchor.constraint(equalTo: self.centerYAnchor).isActive = true
        indicatorView.color = self.tintColor
    }
    
    override func setTitle(_ title: String?, for state: UIControl.State) {
        guard !isAnimating else { return }
        super.setTitle(title, for: state)
        if title?.isEmpty ?? true {
            return
        }
        self.previousText = title
    }
    
    func startAnimating() {
        self.setTitle("", for: .normal)
        indicatorView.startAnimating()
        self.isEnabled = false
    }
    
    func stopAnimating() {
        self.isEnabled = true
        self.indicatorView.stopAnimating()
        self.setTitle(previousText, for: .normal)
    }
    
}

extension String {
    var validOptionalString: String? {
        if self.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty {
            return nil
        }
        return self
    }
}