internal void Refresh(Instrument selectedInstrument = null, Tuning selectedTuning = null)
        {
            DefaultInstruments = AppVM.GetDefaultInstruments();
            UserInstruments    = AppVM.GetUserInstruments();

            if (null == selectedInstrument)
            {
                SelectedInstrument = null;
            }
            else
            {
                foreach (ObservableInstrument oi in UserInstruments)
                {
                    if (oi.Instrument == selectedInstrument)
                    {
                        SelectedInstrument = oi;
                        break;
                    }
                }

                if (null != SelectedInstrument)
                {
                    foreach (ObservableInstrument oi in DefaultInstruments)
                    {
                        if (oi.Instrument == selectedInstrument)
                        {
                            SelectedInstrument = oi;
                            break;
                        }
                    }
                }

                if (null != SelectedInstrument && null != selectedTuning)
                {
                    foreach (ObservableTuning ot in Tunings)
                    {
                        if (ot.Tuning == selectedTuning)
                        {
                            SelectedTuning = ot;
                            break;
                        }
                    }
                }
            }
        }
 public InstrumentManagerViewModel()
 {
     _defaultInstruments = AppVM.GetDefaultInstruments();
     _userInstruments    = AppVM.GetUserInstruments();
 }