Protocol for added pull-to-refresh to any UIScrollView

ScrollToRefreshable.swift

import UIKit

protocol ScrollToRefreshable: UIScrollViewDelegate {
    var refreshableScrollView: UIScrollView { get }
    var activityIndicatorView: UIActivityIndicatorView! { get }

    func updateViewModel()
}

extension ScrollToRefreshable {

    private var pullToRefreshThreshold: CGFloat {
        return 100.00
    }

    var shouldRefresh: Bool {
        let progress = min(1, max(0, -(refreshableScrollView.contentOffset.y + refreshableScrollView.contentInset.top) / pullToRefreshThreshold))
        let hasReachedRefreshThreshold = progress == 1
        let isAlreadyLoading = activityIndicatorView.isAnimating

        return hasReachedRefreshThreshold && !isAlreadyLoading
    }

    func setRefreshDelegate() {
        let scrollView = refreshableScrollView
        scrollView.delegate = self
    }
}

/*
Example usage...

extension MyViewController: ScrollToRefreshable {

    var refreshableScrollView: UIScrollView {
        return tableView as UIScrollView
    }

    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        if shouldRefresh {
            loadData()
        }
    }
}
*/