public ClientInformationViewModel() { clientInfoBL = new ClientInfoBL(); //set up buttons' functions _clearCommand = new DelegateCommand(OnClear); _deleteCommand = new DelegateCommand(OnDelete, CanDelete); _saveCommand = new DelegateCommand(OnSave, CanSave); ResetMessages(); try { //fill in client types _clientTypes = clientInfoBL.GetClientTypes(); if (_clientTypes == null) { _clientTypes = new List <ClientType>(); } } catch (Exception ex) { SetErrorMessage(ex, "loading client types"); return; } try { //fill in client id numbers _clientsIdNumbers = ListToObservableCollection(clientInfoBL.GetClientIdNumbers()); if (_clientsIdNumbers == null) { _clientsIdNumbers = new ObservableCollection <int>(); } } catch (Exception ex) { SetErrorMessage(ex, "loading client id numbers"); return; } SelectedClientIdNumber = null; }