OnReceivedSslError Webview Android

public override void OnReceivedSslError(WebView view, SslErrorHandler handler, SslError error)
            {
                AlertDialog.Builder builder = new AlertDialog.Builder(this.activity);
                AlertDialog ad = builder.Create();
                string message = "Certificate error.";
                switch (error.PrimaryError)
                {
                    case SslErrorType.Untrusted:
                        message = "Certificate is untrusted."; break;
                    case SslErrorType.Expired:
                        message = "Certificate has expired."; break;
                    case SslErrorType.Idmismatch:
                        message = "Certificate ID is mismatched."; break;
                    case SslErrorType.Notyetvalid:
                        message = "Certificate is not yet valid."; break;
                }
                message += " Do you want to continue anyway?";
                ad.SetTitle("SSL Certificate Error");
                ad.SetMessage(message);
                ad.SetButton("OK", (sender, args) =>
                                       {
                                           handler.Proceed();
                                       });
                ad.SetButton2("Cancel", (sender, args) =>
                                            {
                                                handler.Cancel();
                                                activity.Finish();
                                            });
                ad.SetIcon(Android.Resource.Drawable.IcDialogAlert);
                ad.Show();
            }