Cannot get page "like" status using Facebook C# SDK - facebook

Question

I am using the latest Facebook C# SDK (v5.0.40 at time of writing) from here: http://facebooksdk.codeplex.com/.
I have created a test iFrame app in Facebook and got the CSASPNETFacebookApp sample running so that it displays the name of the currently logged in user within Facebook.
What I would now like to do is display different content in my iFrame depending on whether the user has "liked" the page. However the signed_request never seems to contain that information. From what I can see in the FacebookSignedRequest.cs I will only get the payload which contains the page information if the algorithm is AES-256-CBC HMAC-SHA256 but I only ever get HMAC-SHA256 returned.
What am I doing wrong? How do I get it to return the page information? Is it a problem with the setup of my app in Facebook or a configuration issue with the .NET app?
Thanks in advance.

Answer 1

var fb = new FacebookClient("access_token");
dynamic parameters = new ExpandoObject();
parameters.method = "pages.isFan";
parameters.page_id = "{you page id}";
dynamic result = fb.Get(parameters);
bool isFan = result == true;

Answer 2

Neil Knight's answer is technically correct, you can use FQL to look up whether a user has liked a page and it did help to set me on the right path. However my issue was actually more one of set up rather than code. What I didn't understand is that you only receive the "like" information in the signed request if your app is running within the "context of a page". If you set it up correctly then Facebook will pass your app the like flag without the user needing to "Allow" your app.
The steps are:
(1) Create your iframe application in Facebook
(2) Set up a tab url for your app in the app settings. This is what the parent page will use when it generates a link in the left hand column to go to your app.
(3) Go to your "App profile page", the URL will be something like this: http://www.facebook.com/apps/application.php?id=12345 Where 12345 is your app ID.
In the left hand column below the logo image there should be a link "Add to Page". If you click on that link you will be presented with a list of pages that you are the admin for. Select the page you want to like in your app.
Now if you navigate to your page you should get a link to your app in the left hand column. It is only when clicking on that link that you will get the page id and like status passed through to your application.
Hope this helps someone having the same issue.

Answer 3

You could use FQL in order to achieve this. I have just done this using the following statement:
var the_query = FB.Data.query("SELECT uid FROM page_fan WHERE page_id = {0} and uid={1}", page_id, user_id);
In order for this to work, I had to ask the user to "Allow" my application so that I had permission to check to see if they liked the page. Then, it was a simple case of checking the result and displaying the necessary <div>:
the_query.wait(function (rows) {
if (rows.length == 1 && rows[0].uid == user_id) {
$("#myLikeContent").show();
} else {
$("#myNoLikeContent").show();
}
});