A UIButton subclass which can display a loading spinner instead of its title.

LoadingButton.swift

import UIKit

class LoadingButton: UIButton {
    
    // MARK: Public Properties
    
    var spinnerSpeed = 0.75
    var spinnerWidth: CGFloat = 4
    var spinnerRadius = 30
    var isSpinnerRounded = true
    var isLoading: Bool { _isLoading }
    
    // MARK: Private Properties
    
    private var _isLoading = false
    private lazy var spinner: LoadingSpinner = {
        LoadingSpinner(frame: CGRect(x: 0, y: 0, width: spinnerRadius, height: spinnerRadius), speed: spinnerSpeed,
                       color: tintColor, width: spinnerWidth, isRounded: isSpinnerRounded)
    }()
    
    // MARK: Functions
    
    override func awakeFromNib() {
        super.awakeFromNib()
        addSubview(spinner)
        spinner.alpha = 0
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        spinner.center = CGPoint(x: frame.width / 2, y: frame.height / 2)
    }

    func startLoading() {
        if isLoading { return }

        isEnabled = false
        alpha = 1.0
        _isLoading = true
        
        // Fade the title, image and the loading spinner.
        spinner.alpha = 0
        spinner.start()
        UIView.animate(withDuration: 0.25, animations: {
            self.spinner.alpha = 1
            self.titleLabel?.alpha = 0
        })
        
    }
    
    func stopLoading() {
        if !isLoading { return }
        isEnabled = true
        _isLoading = false
        
        // Fade the title, image and the loading spinner.
        UIView.animate(withDuration: 0.25, animations: {
            self.spinner.alpha = 0
            self.titleLabel?.alpha = 1
            self.imageView?.alpha = 1
        })
    }
}