Crash when reallocating WKWebView

PracticeWebView.swift

import UIKit
import WebKit
import XWebView

class LeakAvoider : NSObject, WKScriptMessageHandler {
    weak var delegate : WKScriptMessageHandler?
    init(delegate:WKScriptMessageHandler) {
        self.delegate = delegate
        super.init()
    }
    func userContentController(userContentController: WKUserContentController,
        didReceiveScriptMessage message: WKScriptMessage) {
            self.delegate?.userContentController(
                userContentController, didReceiveScriptMessage: message)
    }
    
    deinit {
        print("leak avoider deinit")
        print("self = \(self.debugDescription)")
    }
}

class PracticeWebView: WKWebView, UIGestureRecognizerDelegate {

   

    func configHandlers(messageHandler: WKScriptMessageHandler?, tag: Int)  {
        
        if let handler = messageHandler {
            let leakHandler = LeakAvoider(delegate: handler)
            configuration.userContentController.addScriptMessageHandler(leakHandler, name: "choiceTapped")
            configuration.userContentController.addScriptMessageHandler(leakHandler, name: "sizeNotification")
            configuration.userContentController.addScriptMessageHandler(leakHandler, name: "pageLoaded")
            configuration.userContentController.addScriptMessageHandler(leakHandler, name: "imageTapped")


            // Get script that's to be injected into the document
            let fastclickScript:WKUserScript =  WKUserScript(source: jsStringFromFileName("fastclick"), injectionTime: WKUserScriptInjectionTime.AtDocumentEnd, forMainFrameOnly: false)
            configuration.userContentController.addUserScript(fastclickScript)
            
            let longPressScript:WKUserScript =  WKUserScript(source: jsStringFromFileName("longPress"), injectionTime: WKUserScriptInjectionTime.AtDocumentEnd, forMainFrameOnly: false)
            configuration.userContentController.addUserScript(longPressScript)
        }
        
        let mainJSScript:WKUserScript =  WKUserScript(source: jsStringFromFileName("main"), injectionTime: WKUserScriptInjectionTime.AtDocumentEnd, forMainFrameOnly: false)
        configuration.userContentController.addUserScript(mainJSScript)
        
        
        let scrollJS = "function scrollTo(element, to, duration) { var start = element.scrollTop, change = to - start, currentTime = 0, increment = 20; var animateScroll = function(){ currentTime += increment; var val = Math.easeInOutQuad(currentTime, start, change, duration); element.scrollTop = val; if(currentTime < duration) { setTimeout(animateScroll, increment); } }; animateScroll(); } Math.easeInOutQuad = function (t, b, c, d) { t /= d/2; if (t < 1) return c/2*t*t + b; t--; return -c/2 * (t*(t-2) - 1) + b; };"
        
        let scrollScript:WKUserScript =  WKUserScript(source: scrollJS, injectionTime: WKUserScriptInjectionTime.AtDocumentEnd, forMainFrameOnly: false)
        configuration.userContentController.addUserScript(scrollScript)
        
        //notify
       let pageLoadedJSString =  "window.onload = function () {window.scrollBy(0, 0); window.webkit.messageHandlers.pageLoaded.postMessage({width: document.width, height: document.height, tag: \(tag)});};"
        let pageLoadedNotificationJS:WKUserScript =  WKUserScript(source: pageLoadedJSString, injectionTime: WKUserScriptInjectionTime.AtDocumentEnd, forMainFrameOnly: false)
        configuration.userContentController.addUserScript(pageLoadedNotificationJS)
        
        let sizeNotificationJSString = "MathJax.Hub.Register.StartupHook('Begin Typeset',function(){console.log('begin')}),MathJax.Hub.Register.StartupHook('End Typeset',function(){console.log('end typeset')}),MathJax.Hub.Register.StartupHook('End',function(){console.log('End');var e=document.getElementsByClassName('math-jax-content');for(console.log(e),j=0;j<e.length;j++){var t=e[j];t.className+=' math-jax-loaded'};window.scrollBy(0, 0); window.webkit.messageHandlers.sizeNotification.postMessage({width: document.width, height: document.height, tag: \(tag)});});"
        let sizeNotificationJS:WKUserScript =  WKUserScript(source: sizeNotificationJSString, injectionTime: WKUserScriptInjectionTime.AtDocumentEnd, forMainFrameOnly: false)
        configuration.userContentController.addUserScript(sizeNotificationJS)
        
        
    }
    
    // Button Click Script to Add to Document
    func jsStringFromFileName(name: String, directory: String? = nil) ->String {
        let results = FileUtils.read(name, type:"js", directory: directory ?? "commonHtmlTemplates")
        return results.content!
    }
    

    deinit {
        print("webview deinit")
        print("self = \(self.debugDescription)")
    }
    
    func scrollToTop() {
        evaluateJavaScript("scrollTo(document.body, 0, 0);", completionHandler: nil)
    }
    
    override func layoutSubviews() {
        scrollToTop()
        let scrollSize = CGSizeMake(frame.width, frame.height)
        scrollView.contentSize = scrollSize
        print("scrollview width = \(scrollView.contentSize.width)")
        
    }

}

extension WKWebView {
    public func viewForZoomingInScrollView(scrollView: UIScrollView) -> UIView? {
        return nil
    }

}

WebViewViewController.swift

   var webView = PracticeWebView()
   
   
     override func viewDidLoad() {
        super.viewDidLoad()
        webView.configHandlers(self, tag: 0)
        webView.translatesAutoresizingMaskIntoConstraints = false
        webView.navigationDelegate = self
        webView.scrollView.delegate = self
        view.addSubview(webView)
        
        let VFLViews = ["webView":webView]
        
        view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|[webView]|", options:NSLayoutFormatOptions.AlignAllCenterX, metrics: nil, views: VFLViews))
        view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|[webView]|", options:NSLayoutFormatOptions.AlignAllCenterX, metrics: nil, views: VFLViews))
    }
    
    override func viewWillDisappear(animated: Bool) {
        super.viewWillDisappear(animated)
        webView.stopLoading()
        webView.configuration.userContentController.removeScriptMessageHandlerForName("choiceTapped")
        webView.configuration.userContentController.removeScriptMessageHandlerForName("sizeNotification")
        webView.configuration.userContentController.removeScriptMessageHandlerForName("pageLoaded")
        webView.configuration.userContentController.removeScriptMessageHandlerForName("imageTapped")
        
    }