Fans-only content in facebook with asp.net C# sdk

Question

Hi i'm developing an application in facebook with c# sdk and i want that the user whom liked my page can only use my application. (Like woobox)

I found some solutions in php in this link but there isn't any source about .net how can i get the liked info in ASP.NET

I find another examples in php in this link again but i can't find c# answer :\

Thanks

Answer 1

You get signed request when your web page is loaded within facebook canvas app; you should be able to parse signed request something similar to following:

if (Request.Params["signed_request"] != null)
{
    string payload = Request.Params["signed_request"].Split('.')[1];
    var encoding = new UTF8Encoding();
    var decodedJson = payload.Replace("=", string.Empty).Replace('-', '+').Replace('_', '/');
    var base64JsonArray = Convert.FromBase64String(decodedJson.PadRight(decodedJson.Length + (4 - decodedJson.Length % 4) % 4, '='));
    var json = encoding.GetString(base64JsonArray);
    var o = JObject.Parse(json);
    var lPid = Convert.ToString(o.SelectToken("page.id")).Replace("\"", "");
    var lLiked = Convert.ToString(o.SelectToken("page.liked")).Replace("\"", "");
    var lUserId= Convert.ToString(o.SelectToken("user_id")).Replace("\"", "");
}

You need to add reference to json libraries in order to parse signed requestin C#, download from http://json.codeplex.com/

Also refere to How to decode OAuth 2.0 for Canvas signed_request in C#? if you are worndering about signed request.

Answer 2

This is only possible with the legacy APIs, or with the user_likes permission. As you want a solution without specific permissions I'll show you 2 methods. Use them in combination with AJAX to refresh the page when a user presses like.

Option 1) REST API

Using the legacy API, it's possible to use Pages.IsFan

https://api.facebook.com/method/pages.isFan?
page_id=...&
uid=...&
access_token=...

Do this in C# as follows.

var appID = "....";
var appSecret = "....";
var uid = "....";
var pageId = "....";

WebClient client = new WebClient();
var appAuthUri = string.Concat("https://graph.facebook.com/oauth/access_token?",
                            "client_id=", appID,
                            "&client_secret=", appSecret,
                            "&grant_type=", "client_credentials"
                            );
var response = client.DownloadString(appAuthUri);
var access_token = response.Split('=')[1];

var isFanUri = string.Concat("https://api.facebook.com/method/pages.isFan?",
                            "format=", "json",
                            "&page_id=", pageId,
                            "&uid=", uid,
                            "&access_token=", access_token
                            );
response = client.DownloadString(isFanUri);
bool isFan;
bool.TryParse(response, out isFan);

Option 2) Client side

The FBXML method. This is done with Javascript on the client, by subscribing to an event when the user clicks the like button. It's documented here.

How do I know when a user clicks a Like button?

If you are using the XFBML version of the button, you can subscribe to the 'edge.create' event through FB.Event.subscribe.

Generate an FBXML like button here.

<div id="fb-root"></div>
<script>(function(d){
  var js, id = 'facebook-jssdk'; if (d.getElementById(id)) {return;}
  js = d.createElement('script'); js.id = id; js.async = true;
  js.src = "//connect.facebook.net/en_US/all.js#appId=132240610207590&xfbml=1";
  d.getElementsByTagName('head')[0].appendChild(js);
}(document));</script>
<div class="fb-like" data-href="http://www.thecodeking.co.uk" data-send="true" data-width="450" data-show-faces="false"></div>

Then subscribe to the edge.create event using the Javascript SDK. Place this code in the document BODY preferably just before the end.

<script type="text/javascript">
<!--
    window.fbAsyncInit = function () {
        FB.init({ appId: '245693305442004', status: true, cookie: true, xfbml: true });
        FB.Event.subscribe('edge.create',
            function (href, widget) {
                // Do something here
                alert('User just liked '+href);

            });
            (function () {
                var e = document.createElement('script'); e.async = true;
                e.src = document.location.protocol + '//connect.facebook.net/en_US/all.js';
                document.getElementById('fb-root').appendChild(e);
            } ());
    };
//-->
</script>

Answer 3

this.canvasAuthorizer = new CanvasAuthorizer {
    Permissions = new[] { "user_about_me", "publish_stream", "offline_access", "user_likes", "friends_about_me" }
};

this.canvasAuthorizer.Authorize();

if (FacebookWebContext.Current.IsAuthorized())
{
    this.facebookWebClient = new FacebookWebClient(FacebookWebContext.Current);

    string requested_Data = HttpContext.Current.Request.Form["signed_request"];
    dynamic decodedSignedRequest = FacebookSignedRequest.Parse(this.facebookApplication, requested_Data);

    if (decodedSignedRequest.Data.page != null)
    {
        // Funs Page
        this.IsLike = decodedSignedRequest.Data.page.liked;
    }
    else
    {
        // Application Page
        dynamic likes = this.facebookWebClient.Get("/me/likes");
        foreach (dynamic like in likes.data)
        {
            if (like.id == this.FacebookFanPageID)
            {
                this.IsLike = true;
            }
        }
    }
}

Answer 4

If your app is a canvas app, you could (should?) use the signed_request parameter to check if the user likes the page it's on:

# pseudocode
signed_request = decode_signed_request()
if signed_request['page']['liked']:
  # user liked page, do something cool
else:
  # user doesn't like page. redirect somewhere to tell them why they should

The signed_request is passed to your page as a POST variable; just as if there was a form field named signed_request and the form was submitted on the page previous to yours (in fact this is basically how facebook "runs" your app; the form is auto-submitted instead of waiting for a user to submit it). So in ASP.net you should be able to get it through the Request object:

Request["signed_request"]

This approach is useful if you're creating a "tab app" for a page; you can detect whether the user liked the page without them granting you extra permissions.