// Events
        private void OnAddTopicException(object sender, AddTopicExceptionEventArgs e)
        {
            if (composer == null || e.SessionId != addTopicSessionId)
                return;

            Dispatcher.BeginInvoke(() =>
            {
                ApplicationBar.IsVisible = true;
                composer.SubjectTextBox.IsEnabled = true;
                composer.MessageTextBox.IsEnabled = true;
                composer.ComposerView.Opacity = 1;

                composer.StatusTextView.Text = AppResources.GroupAddTopicErrorText;
                composer.ProgressView.Visibility = Visibility.Collapsed;
            });
        }
        public void AddTopicAsync(string sessionId, string groupId, string subject, string message)
        {
            string timestamp = DateTimeUtils.GetTimestamp();
            string nonce = Guid.NewGuid().ToString().Replace("-", null);

            Dictionary<string, string> paramDict = new Dictionary<string, string>();
            paramDict["method"] = "flickr.groups.discuss.topics.add";
            paramDict["format"] = "json";
            paramDict["nojsoncallback"] = "1";
            paramDict["oauth_consumer_key"] = consumerKey;
            paramDict["oauth_nonce"] = nonce;
            paramDict["oauth_signature_method"] = "HMAC-SHA1";
            paramDict["oauth_timestamp"] = timestamp;
            paramDict["oauth_token"] = AccessToken;
            paramDict["oauth_version"] = "1.0";
            paramDict["group_id"] = groupId;
            paramDict["subject"] = subject;
            paramDict["message"] = message;

            string signature = OAuthCalculateSignature("POST", "https://api.flickr.com/services/rest/", paramDict, AccessTokenSecret);
            paramDict["oauth_signature"] = signature;

            DispatchPostRequest("POST", "https://api.flickr.com/services/rest/", paramDict, 
                (response) => {

                    bool success = true;
                    string errorMessage = "";

                    try
                    {
                        JObject json = JObject.Parse(response);
                        string status = json["stat"].ToString();
                        if (status != "ok")
                        {
                            success = false;
                            errorMessage = json["message"].ToString();
                        }
                    }
                    catch (Exception e)
                    {
                        Debug.WriteLine(e.Message);

                        success = false;
                    }

                    if (!success)
                    {
                        AddTopicExceptionEventArgs exceptionArgs = new AddTopicExceptionEventArgs();
                        exceptionArgs.SessionId = sessionId;
                        AddTopicException.DispatchEvent(this, exceptionArgs);
                    }
                    else
                    {
                        AddTopicEventArgs args = new AddTopicEventArgs();
                        args.SessionId = sessionId;
                        args.GroupId = groupId;
                        args.Response = response;
                        args.Subject = subject;
                        args.Message = message;
                        TopicAdded.DispatchEvent(this, args);
                    }
                }, (ex) => {
                    AddTopicExceptionEventArgs exceptionArgs = new AddTopicExceptionEventArgs();
                    exceptionArgs.SessionId = sessionId;
                    AddTopicException.DispatchEvent(this, exceptionArgs);
                });

            
        }