import UIKit
import WebKit

class WebViewController: UIViewController {

    @IBOutlet weak var webView: WKWebView!

    override func viewDidLoad() {
        super.viewDidLoad()
        guard let url: URL = Bundle.main.url(forResource: "index", withExtension: "html") else { return }
        webView.scrollView.delegate = self
        webView.loadFileURL(url, allowingReadAccessTo: url)
//        webView.scrollView.pinchGestureRecognizer?.isEnabled = false
//        ↑↑↑この時点で書いてもpinchGestureRecognizerがnilなので意味ない
    }
}

extension WebViewController: UIScrollViewDelegate {
    func scrollViewWillBeginZooming(_ scrollView: UIScrollView, with view: UIView?) {
        scrollView.pinchGestureRecognizer?.isEnabled = false
//      ↑↑↑delegateの中で書いてやると良い
    }
}