private void E_ReceivedMsg(object sender, string e) { if (e.StartsWith("@quit")) { var client = sender as ClientHandler; ConnectedUsers.Remove(client.Username); // remove username } else { App.Current.Dispatcher.Invoke(() => { var client = sender as ClientHandler; ReceivedMsg.Add(client.Username + ":" + e); RaisePropertyChanged(nameof(CountMsg)); if (!ConnectedUsers.Contains(client.Username)) { ConnectedUsers.Add(client.Username); } }); } }