private async void SendMessage()
        {
            if (String.IsNullOrEmpty(MessageText))
            {
                return;
            }

            _uiDispatcher.Invoke(() =>
            {
                IsMessagingAllowed = false;
                IsSendingMessage   = true;
            });

            var message = new Message {
                Content = (string)MessageText.Clone(), Receiver = _selectedUser.Username, TimeStamp = DateTime.Now, Sender = _username
            };
            //TODO: should we use this message or wait it from server?

            var sendMessageTask = _connectionManager.SendMessageAsync(message);

            await sendMessageTask;

            if (sendMessageTask.Result.IsSucessful)
            {
                lock (_messageLock)
                {
                    _allMessages[message.Receiver].Add(message);
                }
                MessageText = String.Empty;
            }
            ;

            _uiDispatcher.Invoke(() =>
            {
                IsSendingMessage   = false;
                IsMessagingAllowed = true;
            });
        }