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

Question

我正在尝试为要在 Parse 服务器上使用的 Xamarin.Android 创建登录系统。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:

1. 登录后，我收到一条成功消息(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。
2. 虽然LoginCompete 代码正在运行应用程序正在后台运行，用户看不到任何内容，就像应用程序关闭后登录再次打开。我尝试用 AlertDialog 显示函数 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 for Android SDK 处理单点登录场景。

只需一些小步骤，您就可以达到预期的结果:

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

2. 设置解析 SDK

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

3. 将 FB 登录按钮添加到您的 View 。

   <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" />   
   

4. 获取回调并使用 token 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
   ... 
   }
   

5. (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

额外的

这里是官方文档的链接: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