Easily apply a loading overlay with interaction restrictions

LoadingOverlayDisplayable.swift

import UIKit

/// Have a UIViewController adopt this to easily block interactions while loading.
protocol LoadingOverlayDisplayable: class {
    var loadingOverlayView: LoadingOverlayView? { get set }
}

extension LoadingOverlayDisplayable where Self: UIViewController {

    /// Call in `viewDidLoad` to establish the loading overlay view
    func addLoadingOverlay() {
        self.loadingOverlayView?.removeFromSuperview()

        let loadingOverlayView = LoadingOverlayView(frame: view.frame)
        view.addSubview(loadingOverlayView)

        loadingOverlayView.translatesAutoresizingMaskIntoConstraints = false
        loadingOverlayView.widthAnchor.constraint(equalTo: view.widthAnchor, constant: 0).isActive = true
        loadingOverlayView.heightAnchor.constraint(equalTo: view.heightAnchor, constant: 0).isActive = true
        loadingOverlayView.centerXAnchor.constraint(equalTo: view.centerXAnchor, constant: 0).isActive = true
        loadingOverlayView.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: 0).isActive = true

        self.loadingOverlayView = loadingOverlayView
    }

    /// Call when you want to show/hide the loading overlay
    func updateLoadingSpinner(isLoading: Bool) {
        DispatchQueue.main.async { [weak self] in
            if isLoading {
                self?.loadingOverlayView?.begin()
            } else {
                self?.loadingOverlayView?.end()
            }
        }
    }
}

class LoadingOverlayView: UIView {
    private var currentProcessesCount: UInt = 0 {
        willSet {
            isHidden = newValue == 0
        }
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

        self.configure()
    }

    override init(frame: CGRect) {
        super.init(frame: frame)

        self.configure()
    }

    private func configure() {
        isHidden = true
        backgroundColor = UIColor.clear

        let dimmerView = UIView(frame: frame)
        dimmerView.backgroundColor = UIColor.black
        dimmerView.alpha = 0.4
        addSubview(dimmerView)

        let indicator = UIActivityIndicatorView(activityIndicatorStyle: .whiteLarge)
        indicator.startAnimating()
        addSubview(indicator)

        dimmerView.translatesAutoresizingMaskIntoConstraints = false
        dimmerView.widthAnchor.constraint(equalTo: self.widthAnchor, constant: 0).isActive = true
        dimmerView.heightAnchor.constraint(equalTo: self.heightAnchor, constant: 0).isActive = true
        dimmerView.centerXAnchor.constraint(equalTo: self.centerXAnchor, constant: 0).isActive = true
        dimmerView.centerYAnchor.constraint(equalTo: self.centerYAnchor, constant: 0).isActive = true

        indicator.translatesAutoresizingMaskIntoConstraints = false
        indicator.centerXAnchor.constraint(equalTo: self.centerXAnchor, constant: 0).isActive = true
        indicator.centerYAnchor.constraint(equalTo: self.centerYAnchor, constant: 0).isActive = true
    }

    func begin() {
        if currentProcessesCount == 0 {
            UIApplication.shared.beginIgnoringInteractionEvents()
        }
        currentProcessesCount += 1

    }

    func end() {
        if currentProcessesCount > 0 {
            currentProcessesCount -= 1
        }
        if currentProcessesCount == 0 {
            UIApplication.shared.endIgnoringInteractionEvents()
        }
    }
}