使用 Xamarin.Android 为 Parse.com 服务器制作更漂亮的 Facebook 登录屏幕

Question

我正在尝试为 Xamarin.Android 创建一个登录系统，以便在 Parse 服务器上使用。我想用 Facebook 登录用户并保存他的真实姓名和他的小用户照片。我当前显示登录系统的代码是这样的：

using Xamarin.Auth;

loginFacebookButton.Click += (sender, e) =>
        {

            if (CrossConnectivity.Current.IsConnected)
                LoginToFacebook();
            else
            {
                DisplayNoConnectivityMessage();
            }

        };

        loginTwitterButton.Click += (sender, e) =>
        {
            LoginToTwitter();
        };
    }

    void DisplayNoConnectivityMessage()
    {
        AlertDialog.Builder alert2 = new AlertDialog.Builder(this);
        alert2.SetTitle("Network error");
        alert2.SetMessage("Connection with the Internet is required. Please check your connectivity and try again.");
        alert2.Show();

    }

    void DisplayLoadingMessage(bool Dismiss)
    {
        RunOnUiThread(() =>
        {
            if (!Dismiss)
            {
                builder = new AlertDialog.Builder(this);

                builder.SetTitle("Signing in");
                builder.SetMessage("Please wait...");
                builder.SetCancelable(false);
                alert = builder.Create();
                alert.Show();

            } else {
                if (alert != null)
                    if (alert.IsShowing)
                    { 
                        alert.Dismiss();
                        alert.Dispose();
                    }
            }
        });

    }

    async void LoginToFacebook()
    {
        var auth = new OAuth2Authenticator(
            clientId: "809804315805408",
            scope: "user_about_me",
            authorizeUrl: new Uri("https://m.facebook.com/dialog/oauth/"),
            redirectUrl: new Uri("http://www.facebook.com/connect/login_success.html")
        );

        auth.AllowCancel = false;

        // If authorization succeeds or is canceled, .Completed will be fired.
        auth.Completed += LoginComplete;

        var intent = auth.GetUI(this);
        StartActivity(intent);
    }

    public async void LoginComplete(object sender, AuthenticatorCompletedEventArgs e)
    {
        string id = "";
        string name = "";
        JsonValue obj;
        if (!e.IsAuthenticated)
        {
            var builder = new AlertDialog.Builder(this);
            builder.SetMessage("Not Authenticated");
            builder.SetPositiveButton("Ok", (o, c) => { });
            builder.Create().Show();
            return;
        }
        else {

            DisplayLoadingMessage(false);
            AccountStore.Create(this) .Save(e.Account, "Facebook");
            // Now that we're logged in, make a OAuth2 request to get the user's info.
            var request = new OAuth2Request("GET", new Uri("https://graph.facebook.com/me"), null, e.Account);
            await request.GetResponseAsync().ContinueWith(t =>
            {
                var builder2 = new AlertDialog.Builder(this);
                if (t.IsFaulted)
                {
                    builder2.SetTitle("Error");
                    builder2.SetMessage(t.Exception.Flatten().InnerException.ToString());
                    builder2.Show();
                }
                else if (t.IsCanceled)
                {
                    builder2.SetTitle("Task Canceled");
                    builder2.Show();
                }
                else {
                    obj = JsonValue.Parse(t.Result.GetResponseText());
                    id = obj["id"];
                    name = obj["name"];
                }

                builder.SetPositiveButton("Ok", (o, c) => { });
                builder.Create();
            }, UIScheduler);

            var accessToken = e.Account.Properties["access_token"];
            var expiresIn = Convert.ToDouble(e.Account.Properties["expires_in"]);
            var expiryDate = DateTime.Now + TimeSpan.FromSeconds(expiresIn);
            var user = await ParseFacebookUtils.LogInAsync(id, accessToken, expiryDate);

            try
            {
                user.Add("Name", name);
            }
            catch (Exception ex)
            {
                Console.WriteLine("LoginFragment.cs | LoginComplete() :: user.Add (\"Name\",name); :: " + ex.Message);
            }

            var webClient = new WebClient();
            //var httpClient = new HttpClient(new NativeMessageHandler());
            var url = new Uri("http://graph.facebook.com/" + id + "/picture?type=small");
            application.currentUserImageUrl = url.ToString();
            application.currentUserName = name;
            byte[] bytes = null;
            //bytes = await httpClient.GetByteArrayAsync(url);
            bytes = await webClient.DownloadDataTaskAsync(url);

            ParseFile saveImageFile = new ParseFile("profileImage.jpg", bytes);
            try
            {
                user.Add("profile_pic", saveImageFile);
            }
            catch (Exception ex)
            {
                Console.WriteLine("LoginFragment.cs | LoginComplete() :: user.Add (\"profile_pic\",saveImageFile); :: " + ex.Message);
            }

            application.currentUser = user;
            await user.SaveAsync();
            DisplayLoadingMessage(true);
            ChangeScreen();
        }
    }

这段代码的问题是：

登录后，我收到成功消息（一个简单的白页上的成功消息）必须来自 facebook 和显然我不想显示在用户身上。
虽然 LoginCompete 代码是运行应用程序在后台运行，用户看不到任何内容，就像应用程序关闭后登录再次打开。我尝试显示一个 AlertDialog 函数 DisplayNoConnectivityMessage 但未显示在用户中任何我不知道的方式。

Answer 1

在 Parse 上使用 Facebook 登录的最简单方法是官方 Parse SDK 结合官方 Facebook Android SDK 来处理单点登录场景。

只需一些小步骤即可达到预期结果：

按照这个小指南为 Facebook SDK 设置您的应用程序：https://components.xamarin.com/gettingstarted/facebookandroid

设置 Parse SDK

public App()
{
    // App.xaml initialization
    ParseClient.Initialize("Your Application ID", "Your .NET Key");
    ParseFacebookUtils.Initialize("Your Facebook App Id");
    // Other initialization
}

将 FB 登录按钮添加到您的视图。

<com.facebook.login.widget.LoginButton
  android:id="@+id/login_button"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_gravity="center_horizontal"
  android:layout_marginTop="30dp"
  android:layout_marginBottom="30dp" />

获取回调并使用令牌通过 Parse 登录用户。

public class MainActivity : Activity, IFacebookCallback
{
    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

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

        var callbackManager = CallbackManagerFactory.Create();

        var loginButton = FindViewById<LoginButton>(Resource.Id.login_button);
        loginButton.RegisterCallback(callbackManager, this);
    }

    #region IFacebookCallback

    public void OnCancel()
    {
        // Handle Cancel
    }

    public void OnError(FacebookException error)
    {
        // Handle Error
    }

    public async void OnSuccess(Object result)
    {
        // We know that this is a LoginResult
        var loginResult = (LoginResult) result;

        // Convert Java.Util.Date to DateTime
        var epoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
        var expireDate = epoch.AddMilliseconds(loginResult.AccessToken.Expires.Time);

        // FB User AccessToken
        var accessToken = loginResult.AccessToken.Token;

        ParseUser user = await ParseFacebookUtils.LogInAsync("Your Facebook App Id", accessToken, expireDate);
    }

    #endregion
... 
}

（可选）与 Facebook SDK 和 ParseUser 交互

// You can simply pass the acquired AccessToken to the GraphRequest
var parameters = new Bundle();
parameters.PutString("fields", "id,email,gender,cover,picture.type(small)");
var request = new GraphRequest(loginResult.AccessToken, "me", parameters, HttpMethod.Get);

// Execute request and Handle response (See FB Android SDK Guide)
// to get image as byte[] from GraphResponse
byte[] data;

// Store the image into the ParseUser
user["image"] = new ParseFile("image.jpg", data);

Instead of using the GraphRequest you can always fallback to the HttpClient / WebClient and pass the AccessToken as URL parameter. Docs

额外

这里是官方文档的link：http://parseplatform.github.io/docs/dotnet/guide/#facebook-users

从 Nuget 中选择 SDK：https://www.nuget.org/packages/Xamarin.Facebook.Android/

Xamarin Facebook Android SDK 的工作方式类似于 Java SDK，因此该文档也值得一看：https://developers.facebook.com/docs/facebook-login/android#addbutton

Answer 2

我的问题终于是：

通过在 facebook 开发人员仪表板中禁用 facebook 登录应用程序设置的安全浏览，我能够获得成功消息的肋骨。
将 Activity 设置为“NoHistory = true”，会使社交登录出现问题，导致社交平台对 Activity 未按应有的方式进行跟踪。这也是没有显示 AlertDialog 的问题（我永远不会猜到）。

但是 @paul-reichelt 的回答是本机 facebook 登录的最佳方法。

使用 Xamarin.Android 为 Parse.com 服务器制作更漂亮的 Facebook 登录屏幕

Making a prettier Facebook Login Screen for Parse.com Server with Xamarin.Android

c#

android

facebook-login

parse-platform

xamarin