Java.Lang.ClassNotFoundException WebAuthenticatorActivity

Question

我有一个Xamarin.android项目，我想使用Xamarin.Auth包让用户通过Google登录页面进行身份验证。

这是我在MainActivity.cs的代码

OAuth2Authenticator auth = new OAuth2Authenticator
        (
            clientId: "client-id.apps.googleusercontent.com",
            scope: "",
            authorizeUrl: new Uri("https://accounts.google.com/o/oauth2/v2/auth"),
            redirectUrl: new Uri("http://www.facebook.com/connect/login_success.html"),
            // switch for new Native UI API
            //      true = Android Custom Tabs and/or ios Safari View Controller
            //      false = Embedded Browsers used (Android WebView, iOS UIWebView)
            //  default = false  (not using NEW native UI)
            isUsingNativeUI: false
        );

        auth.Completed += (sender, eventArgs) =>
        {
            // UI presented, so it's up to us to dimiss it on Android
            // dismiss Activity with WebView or CustomTabs
            this.Finish();

            if (eventArgs.IsAuthenticated)
            {
                // Use eventArgs.Account to do wonderful things
            }
            else
            {
                // The user cancelled
            }
        };

        var ui_object = auth.GetUI(this);
        StartActivity(ui_object);

        // Set our view from the "main" layout resource
        SetContentView(Resource.Layout.Main);

在调用auth.GetUI（this）方法时，我始终以下面的异常结束：

JNIEnv.FindClass(Type) caught unexpected exception: Java.Lang.ClassNotFoundException: md53c585be971e02235139fd1aef11fc0c1.WebAuthenticatorActivity ---> Java.Lang.ClassNotFoundException: Didn't find class "md53c585be971e02235139fd1aef11fc0c1.WebAuthenticatorActivity"

任何人都可以看到为什么会这样做？我试图谷歌它，但看起来我只是一个谁得到这种类型的错误。

我有VS 2017 15.5.2并使用Android 8.0 API 26