Xamarin.iOS WKWebView在调用时无法呈现

我在我的Xamarin.Forms项目中实现了自定义webview渲染器（遵循本教程：https://developer.xamarin.com/guides/xamarin-forms/application-fundamentals/custom-renderer/hybridwebview/） . 在Android中一切正常，但这不是可见的 . 我需要在WebView区域中点击一次，以便显示内容 . WKWebView中是否有任何强制WebView内容的可见性/呈现？这是我的适用于iOS的HybridWebViewRenderer类：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Foundation;
using UIKit;
using Xamarin.Forms.Platform.iOS;
using Xamarin.Forms;
using System.IO;
using WebKit;

[assembly: ExportRenderer(typeof(MyProject.HybridWebView), typeof(MyProject.iOS.HybridWebViewRenderer))]
namespace MyProject.iOS
{
    public class HybridWebViewRenderer : ViewRenderer<HybridWebView, WKWebView>, IWKScriptMessageHandler
    {
        const string JavaScriptFunction = @"var meta = document.createElement('meta'); meta.setAttribute('name', 'viewport'); meta.setAttribute('content', 'width=device-width'); document.getElementsByTagName('head')[0].appendChild(meta); function invokeCSharpAction(data){window.webkit.messageHandlers.invokeAction.postMessage(data);}";
        WKUserContentController userController;

        protected override void     OnElementChanged(ElementChangedEventArgs<HybridWebView> e)
        {
            base.OnElementChanged(e);

            if (Control == null)
            {
                userController = new WKUserContentController();
                var script = new WKUserScript(new NSString(JavaScriptFunction), WKUserScriptInjectionTime.AtDocumentEnd, false);
                userController.AddUserScript(script);
                userController.AddScriptMessageHandler(this, "invokeAction");

                var config = new WKWebViewConfiguration { UserContentController = userController };
                var webView = new WKWebView(Frame, config);
                SetNativeControl(webView);

                webView.Opaque = false;
                webView.BackgroundColor = UIColor.Clear;
                webView.ScrollView.ScrollEnabled = false;
                webView.ScrollView.Bounces = false;
            }
            if (e.OldElement != null)
            {
                userController.RemoveAllUserScripts();
                userController.RemoveScriptMessageHandler("invokeAction");
                var hybridWebView = e.OldElement as HybridWebView;
                hybridWebView.Cleanup();
            }
            if (e.NewElement != null)
            {
                string fileName = Path.Combine(NSBundle.MainBundle.BundlePath, string.Format("Content/{0}", Element.Uri));
                Control.LoadRequest(new NSUrlRequest(new NSUrl(fileName, false)));
            }
        }

        public void DidReceiveScriptMessage(WKUserContentController userContentController, WKScriptMessage message)
        {
            Element.InvokeAction(message.Body.ToString());
        }
    }
}