C# Xamarin使用CustomWebViewClient形成Android Web视图在加载特定站点后停止工作

为了使用我的WebView发送身份验证标头，我有自定义WebViewRenderer和WebViewClient

可以为各种URL创建、加载、关闭并重新创建带有此控件的Xamarin forms页面，而不会出现任何问题。但是，在访问特定站点后，WebView将不再加载任何URL，并且根本不会调用ShouldInterceptRequest，即使在使用此控件关闭并创建新页面后也是如此

例如：

打开MyWebViewPage至www.google.com。成功

关闭MyWebViewPage

打开MyWebViewPage至www.bing.com。成功

关闭MyWebViewPage

打开MyWebViewPage至mywebapp.local（问题页面）成功

关闭MyWebViewPage

打开MyWebViewPage至www.google.com。失败，页面不呈现

如果没有CustomWebViewClient，则不会出现此问题（但是我需要将此用于标题）

我正在寻找直接修复此问题的方法，或者完全重置此控件/页面的方法。 不适合对网站进行修复，因为这可能并不总是可能的

调试上次成功满载的输出（到问题站点）

调试后续故障加载的输出（到相同或其他站点），空白页：

12-04 16:45:36.910 I/art     (23188): Starting a blocking GC Explicit
12-04 16:45:36.941 I/art     (23188): Explicit concurrent mark sweep GC freed 5227(440KB) AllocSpace objects, 24(3MB) LOS objects, 62% free, 4MB/12MB, paused 302us total 31.346ms
12-04 16:45:36.943 D/Mono    (23188): GC_TAR_BRIDGE bridges 362 objects 8823 opaque 2742 colors 362 colors-bridged 362 colors-visible 362 xref 0 cache-hit 0 cache-semihit 0 cache-miss 0 setup 0.11ms tarjan 9.11ms scc-setup 0.23ms gather-xref 0.01ms xref-setup 0.02ms cleanup 0.28ms
12-04 16:45:36.943 D/Mono    (23188): GC_BRIDGE: Complete, was running for 35.88ms
12-04 16:45:36.943 D/Mono    (23188): GC_MINOR: (Nursery full) time 18.20ms, stw 20.86ms promoted 187K major size: 4400K in use: 3752K los size: 13432K in use: 11411K
12-04 16:45:36.973 W/cr_AwContents(23188): onDetachedFromWindow called when already detached. Ignoring
12-04 16:45:36.979 I/cr_Ime  (23188): ImeThread is not enabled.

using Xamarin.Forms;
using MyApp.Droid;

[assembly: ExportRenderer(typeof(WebView), typeof(CustomWebViewRenderer))]
namespace MyApp.Droid
{        
    using Android.OS;
    using global::Xamarin.Forms.Platform.Android;
    using Android.Content;
    using System;

    public class CustomWebViewRenderer : WebViewRenderer
    {        
        public CustomWebViewRenderer(Context context) : base(context)
        {
        }

        public IWebViewController GetElementController()
        {
            return Element;
        }

        protected override void OnElementChanged(ElementChangedEventArgs<global::Xamarin.Forms.WebView> e)
        {
            try
            {
                base.OnElementChanged(e);

                if (Control != null && e.NewElement != null)
                {
                    SetupControlSettings();
                }
            }
            catch (Exception ex)
            {
                Logging.LogException(ex);
            }
        }           

        private void SetupControlSettings()
        {
            try
            {   
                if (Build.VERSION.SdkInt >= BuildVersionCodes.JellyBeanMr1)
                {
                    Control.Settings.MediaPlaybackRequiresUserGesture = false;
                    Control.Settings.JavaScriptEnabled = true;
                    Control.Settings.AllowContentAccess = true;
                    Control.Settings.DomStorageEnabled = true;
                }

                if ((int)Build.VERSION.SdkInt >= 19)
                {
                    Control.SetLayerType(Android.Views.LayerType.Hardware, null);
                }
                else
                {
                    Control.SetLayerType(Android.Views.LayerType.Software, null);
                }

                Control.Settings.SetAppCacheMaxSize(10 * 1024 * 1024);
                Control.Settings.AllowFileAccess = true;
                Control.Settings.AllowUniversalAccessFromFileURLs = true;
                Control.Settings.SetAppCacheEnabled(true);
                Control.Settings.CacheMode = Android.Webkit.CacheModes.NoCache;    

                var webViewClient = new CustomWebViewClient(this, MyApp.GlobalVariables.AuthToken);               

                Control.SetWebViewClient(webViewClient);

            }
            catch (Exception ex)
            {
                Logging.LogException(ex);
            }
        }   
    }
}

using Android.Webkit;
using System;
using System.Net.Http;
using Xamarin.Forms;

namespace MyApp.Droid
{
    public class CustomWebViewClient : WebViewClient
    {
        private readonly string authToken;
        private readonly CustomWebViewRenderer renderer;
        public CustomWebViewClient(CustomWebViewRenderer renderer, string authToken)
        {
            this.renderer = renderer;
            this.authToken = authToken;
        }


        public override bool ShouldOverrideUrlLoading(Android.Webkit.WebView view, IWebResourceRequest request)
        {
            WebNavigatingEventArgs args = new WebNavigatingEventArgs(WebNavigationEvent.NewPage, new UrlWebViewSource { Url = request.Url.ToString() }, request.Url.ToString());
            renderer.GetElementController().SendNavigating(args);

            if (args.Cancel)
            {
                view.StopLoading();
            }

            return base.ShouldOverrideUrlLoading(view, request);
        }


        public override WebResourceResponse ShouldInterceptRequest(Android.Webkit.WebView view, IWebResourceRequest request)
        {
            try
            {
                if (!string.IsNullOrWhiteSpace(authToken))
                {
                    string authorizationValue = "Bearer " + authToken;    
                    using (HttpClient client = new HttpClient())
                    {    
                        request.RequestHeaders.Add("Authorization", authorizationValue);    
                        foreach(var h in request.RequestHeaders)
                        {
                            if (client.DefaultRequestHeaders.Contains(h.Key))
                            {
                                client.DefaultRequestHeaders.Remove(h.Key);
                            }  
                            client.DefaultRequestHeaders.Add(h.Key,h.Value);                            
                        }    
                        HttpResponseMessage response = client.GetAsync(request.Url.ToString()).Result;

                        string encoding = response.Content.Headers.ContentEncoding.GetEnumerator().Current;
                        string contentType = response.Content.Headers.ContentType.ToString();
                        System.IO.Stream stream = response.Content.ReadAsStreamAsync().Result;

                        if (string.IsNullOrWhiteSpace(encoding) && contentType.Contains(";"))
                        {
                            string[] parts = contentType.Split(';');
                            contentType = parts[0].Trim();
                            encoding = parts[1].Trim();
                        }

                        WebResourceResponse result = new WebResourceResponse(contentType, encoding, stream);    
                        return result;
                    }
                }
            }
            catch (Exception ex)
            {
                Logging.LogException(ex);
            }

            return base.ShouldInterceptRequest(view, request);
        }


        public override void OnPageFinished(Android.Webkit.WebView view, string url)
        {
            try
            {
                base.OnPageFinished(view, url);

                UrlWebViewSource source = new UrlWebViewSource { Url = url };
                WebNavigatedEventArgs args = new WebNavigatedEventArgs(WebNavigationEvent.NewPage, source, url, WebNavigationResult.Success);
                renderer?.GetElementController()?.SendNavigated(args);
            }
            catch (Exception ex)
            {
                Logging.LogException(ex);
            }
        } 
    }
}

WebViewRenderer:

12-04 16:45:36.910 I/art     (23188): Starting a blocking GC Explicit
12-04 16:45:36.941 I/art     (23188): Explicit concurrent mark sweep GC freed 5227(440KB) AllocSpace objects, 24(3MB) LOS objects, 62% free, 4MB/12MB, paused 302us total 31.346ms
12-04 16:45:36.943 D/Mono    (23188): GC_TAR_BRIDGE bridges 362 objects 8823 opaque 2742 colors 362 colors-bridged 362 colors-visible 362 xref 0 cache-hit 0 cache-semihit 0 cache-miss 0 setup 0.11ms tarjan 9.11ms scc-setup 0.23ms gather-xref 0.01ms xref-setup 0.02ms cleanup 0.28ms
12-04 16:45:36.943 D/Mono    (23188): GC_BRIDGE: Complete, was running for 35.88ms
12-04 16:45:36.943 D/Mono    (23188): GC_MINOR: (Nursery full) time 18.20ms, stw 20.86ms promoted 187K major size: 4400K in use: 3752K los size: 13432K in use: 11411K
12-04 16:45:36.973 W/cr_AwContents(23188): onDetachedFromWindow called when already detached. Ignoring
12-04 16:45:36.979 I/cr_Ime  (23188): ImeThread is not enabled.

using Xamarin.Forms;
using MyApp.Droid;

[assembly: ExportRenderer(typeof(WebView), typeof(CustomWebViewRenderer))]
namespace MyApp.Droid
{        
    using Android.OS;
    using global::Xamarin.Forms.Platform.Android;
    using Android.Content;
    using System;

    public class CustomWebViewRenderer : WebViewRenderer
    {        
        public CustomWebViewRenderer(Context context) : base(context)
        {
        }

        public IWebViewController GetElementController()
        {
            return Element;
        }

        protected override void OnElementChanged(ElementChangedEventArgs<global::Xamarin.Forms.WebView> e)
        {
            try
            {
                base.OnElementChanged(e);

                if (Control != null && e.NewElement != null)
                {
                    SetupControlSettings();
                }
            }
            catch (Exception ex)
            {
                Logging.LogException(ex);
            }
        }           

        private void SetupControlSettings()
        {
            try
            {   
                if (Build.VERSION.SdkInt >= BuildVersionCodes.JellyBeanMr1)
                {
                    Control.Settings.MediaPlaybackRequiresUserGesture = false;
                    Control.Settings.JavaScriptEnabled = true;
                    Control.Settings.AllowContentAccess = true;
                    Control.Settings.DomStorageEnabled = true;
                }

                if ((int)Build.VERSION.SdkInt >= 19)
                {
                    Control.SetLayerType(Android.Views.LayerType.Hardware, null);
                }
                else
                {
                    Control.SetLayerType(Android.Views.LayerType.Software, null);
                }

                Control.Settings.SetAppCacheMaxSize(10 * 1024 * 1024);
                Control.Settings.AllowFileAccess = true;
                Control.Settings.AllowUniversalAccessFromFileURLs = true;
                Control.Settings.SetAppCacheEnabled(true);
                Control.Settings.CacheMode = Android.Webkit.CacheModes.NoCache;    

                var webViewClient = new CustomWebViewClient(this, MyApp.GlobalVariables.AuthToken);               

                Control.SetWebViewClient(webViewClient);

            }
            catch (Exception ex)
            {
                Logging.LogException(ex);
            }
        }   
    }
}

using Android.Webkit;
using System;
using System.Net.Http;
using Xamarin.Forms;

namespace MyApp.Droid
{
    public class CustomWebViewClient : WebViewClient
    {
        private readonly string authToken;
        private readonly CustomWebViewRenderer renderer;
        public CustomWebViewClient(CustomWebViewRenderer renderer, string authToken)
        {
            this.renderer = renderer;
            this.authToken = authToken;
        }


        public override bool ShouldOverrideUrlLoading(Android.Webkit.WebView view, IWebResourceRequest request)
        {
            WebNavigatingEventArgs args = new WebNavigatingEventArgs(WebNavigationEvent.NewPage, new UrlWebViewSource { Url = request.Url.ToString() }, request.Url.ToString());
            renderer.GetElementController().SendNavigating(args);

            if (args.Cancel)
            {
                view.StopLoading();
            }

            return base.ShouldOverrideUrlLoading(view, request);
        }


        public override WebResourceResponse ShouldInterceptRequest(Android.Webkit.WebView view, IWebResourceRequest request)
        {
            try
            {
                if (!string.IsNullOrWhiteSpace(authToken))
                {
                    string authorizationValue = "Bearer " + authToken;    
                    using (HttpClient client = new HttpClient())
                    {    
                        request.RequestHeaders.Add("Authorization", authorizationValue);    
                        foreach(var h in request.RequestHeaders)
                        {
                            if (client.DefaultRequestHeaders.Contains(h.Key))
                            {
                                client.DefaultRequestHeaders.Remove(h.Key);
                            }  
                            client.DefaultRequestHeaders.Add(h.Key,h.Value);                            
                        }    
                        HttpResponseMessage response = client.GetAsync(request.Url.ToString()).Result;

                        string encoding = response.Content.Headers.ContentEncoding.GetEnumerator().Current;
                        string contentType = response.Content.Headers.ContentType.ToString();
                        System.IO.Stream stream = response.Content.ReadAsStreamAsync().Result;

                        if (string.IsNullOrWhiteSpace(encoding) && contentType.Contains(";"))
                        {
                            string[] parts = contentType.Split(';');
                            contentType = parts[0].Trim();
                            encoding = parts[1].Trim();
                        }

                        WebResourceResponse result = new WebResourceResponse(contentType, encoding, stream);    
                        return result;
                    }
                }
            }
            catch (Exception ex)
            {
                Logging.LogException(ex);
            }

            return base.ShouldInterceptRequest(view, request);
        }


        public override void OnPageFinished(Android.Webkit.WebView view, string url)
        {
            try
            {
                base.OnPageFinished(view, url);

                UrlWebViewSource source = new UrlWebViewSource { Url = url };
                WebNavigatedEventArgs args = new WebNavigatedEventArgs(WebNavigationEvent.NewPage, source, url, WebNavigationResult.Success);
                renderer?.GetElementController()?.SendNavigated(args);
            }
            catch (Exception ex)
            {
                Logging.LogException(ex);
            }
        } 
    }
}

编辑1: 这似乎是由于以下代码：

HttpResponseMessage response = client.GetAsync(request.Url.ToString()).Result;

如果我注释掉WebResourceResponse返回（因此它落在基本方法上），但将其保留在问题中，则问题仍然存在，但注释这一行可以使它工作

编辑2: 情节越来越复杂。 问题站点使用信号器进行事件通知。 添加一些日志后，我可以看到WebViewClient开始加载 …/signalr/connect？transport=serverSentEvents&connectionToken=

---

但永远不会结束，我猜这就是signar在服务器上的事件发生后才响应的方式。但是，这会阻止对WebViewClient的后续调用

我对您所说的感到困惑，请您发布有关您的问题的更多详细信息，好吗？到底出了什么问题？我已经更新了一个例子。基本上，在访问特定站点之后，即使在重新加载页面之后，web视图也会停止工作（我认为Xamarin会恢复本机控件）。删除ShouldInterceptRequest中的代码修复了该问题，但删除了发送身份验证标头的功能。似乎与服务器上的Signal相关。请查看我的上述编辑可能的解决方案，但需要转换为C#我对您所说的感到困惑，请发布有关您问题的更多详细信息？到底出了什么问题？我已经更新了一个例子。基本上，在访问特定站点之后，即使在重新加载页面之后，web视图也会停止工作（我认为Xamarin会恢复本机控件）。删除ShouldInterceptRequest中的代码修复了此问题，但删除了发送身份验证标头的功能。似乎与服务器上的SignalR有关。请参见此处的“我的编辑”可能的解决方案，但需要转换为C#