Checking if a User Subscribes to a List

Determine if a user subscribes to a list.

Entity: List

Type: ListType.IsSubscriber

Parameters/Filters:

Name	Purpose	Type	Required
IncludeEntities	Add entities to tweets (default: true)	bool	no
ListID	ID of list	ulong	only is Slug is empty
OwnerID	ID of list owner	ulong	only if Slug is provided
OwnerScreenName	Name of list owner	string	only if Slug is provided
ScreenName	ScreenName of user	string	only if UserID is empty
SkipStatus	Exclude status information	bool	no
Slug	Short list name	string	only if ListID is empty
UserID	ID of user	ulong	only if ScreenName is empty

Note: Either UserID or ScreenName is required. Either ListID or Slug is required. If you use Slug, you must also specify either OwnerID or OwnerScreenName.

v3.0 Example:

            try
            {
                var subscribedList =
                    await
                    (from list in twitterCtx.List
                     where list.Type == ListType.IsSubscriber &&
                           list.ScreenName == "JoeMayo" &&
                           list.Slug == "linq" &&
                           list.OwnerScreenName == "Linq2Tweeter"
                     select list)
                    .SingleOrDefaultAsync();

                if (subscribedList != null && subscribedList.Users != null)
                {
                    // list will have only one user matching ID in query
                    var user = subscribedList.Users.First();

                    Console.WriteLine("User: {0} is subscribed to List: {1}",
                        user.Name, subscribedList.ListID); 
                }
            }
            // whenever user is not subscribed to the specified list, Twitter
            // returns an HTTP 404, Not Found, response.  LINQ to Twitter 
            // intercepts the HTTP response and wraps it in a TwitterQueryException 
            // where you can read the error message from Twitter via the Message property.
            catch (TwitterQueryException ex)
            {
                if (ex.StatusCode == HttpStatusCode.NotFound)
                {
                    Console.WriteLine(
                        "HTTP Status Code: {0}. Twitter Error Code: {1}, Twitter Message: {2}",
                        ex.StatusCode.ToString(),
                        ex.ErrorCode,
                        ex.Message);
                }
                else
                {
                    throw ex;
                }
            }

v2.1 Example:

            try
            {
                var subscribedList =
                   (from list in twitterCtx.List
                    where list.Type == ListType.IsSubscribed &&
                          list.ScreenName == "Linq2Tweeter" &&
                          list.Slug == "dotnettwittterdevs" &&
                          list.OwnerScreenName == "JoeMayo"
                    select list)
                   .FirstOrDefault();

                // list will have only one user matching ID in query
                var user = subscribedList.Users.First();

                Console.WriteLine("User: {0} is subscribed to List: {1}",
                    user.Name, subscribedList.ListID);
            }
            // whenever user is not subscribed to the specified list, Twitter
            // returns an HTTP 404, Not Found, response, which results in a
            // .NET exception.  LINQ to Twitter intercepts the HTTP exception
            // and wraps it in a TwitterQueryResponse where you can read the
            // error message from Twitter via the Response property, shown below.
            catch (TwitterQueryException ex)
            {
                // TwitterQueryException will always reference the original
                // WebException, so the check is redundant but doesn't hurt
                var webEx = ex.InnerException as WebException;
                if (webEx == null) throw ex;

                // The response holds data from Twitter
                var webResponse = webEx.Response as HttpWebResponse;
                if (webResponse == null) throw ex;

                if (webResponse.StatusCode == HttpStatusCode.NotFound)
                {
                    Console.WriteLine(
                        "HTTP Status Code: {0}. Response from Twitter: {1}",
                        webEx.Response.Headers["Status"],
                        ex.Response.Error);
                }
                else
                {
                    throw ex;
                }
            }

Note: Twitter returns HTTP 404 Not Found, which becomes a .NET exception, when user is not subscribed.

Twitter API: lists/subscribers/show