How to get the Facebook user id using the access token

If you want to use Graph API to get current user ID then just send a request to:

https://graph.facebook.com/me?access_token=...

The easiest way is

https://graph.facebook.com/me?fields=id&access_token="xxxxx"

then you will get json response which contains only userid.

The facebook acess token looks similar too "1249203702|2.h1MTNeLqcLqw__.86400.129394400-605430316|-WE1iH_CV-afTgyhDPc"

if you extract the middle part by using | to split you get

2.h1MTNeLqcLqw__.86400.129394400-605430316

then split again by -

the last part 605430316 is the user id.

Here is the C# code to extract the user id from the access token:

   public long ParseUserIdFromAccessToken(string accessToken)
   {
        Contract.Requires(!string.isNullOrEmpty(accessToken);

        /*
         * access_token:
         *   1249203702|2.h1MTNeLqcLqw__.86400.129394400-605430316|-WE1iH_CV-afTgyhDPc
         *                                               |_______|
         *                                                   |
         *                                                user id
         */

        long userId = 0;

        var accessTokenParts = accessToken.Split('|');

        if (accessTokenParts.Length == 3)
        {
            var idPart = accessTokenParts[1];
            if (!string.IsNullOrEmpty(idPart))
            {
                var index = idPart.LastIndexOf('-');
                if (index >= 0)
                {
                    string id = idPart.Substring(index + 1);
                    if (!string.IsNullOrEmpty(id))
                    {
                        return id;
                    }
                }
            }
        }

        return null;
    }

WARNING: The structure of the access token is undocumented and may not always fit the pattern above. Use it at your own risk.

Update Due to changes in Facebook. the preferred method to get userid from the encrypted access token is as follows:

try
{
    var fb = new FacebookClient(accessToken);
    var result = (IDictionary<string, object>)fb.Get("/me?fields=id");
    return (string)result["id"];
}
catch (FacebookOAuthException)
{
    return null;
}

You can use below code on onSuccess(LoginResult loginResult)

loginResult.getAccessToken().getUserId();