//TODO: add methods to create viewmodels for models, storing the id to retrieve any existing viewmodel if already created.
 public NoteViewModel GetViewModel(INote model)
 {
     NoteViewModel vm;
     if (noteViewModels.ContainsKey(model.ID))
     {
         vm = noteViewModels[model.ID];
         vm.Model = model;
     }
     else
     {
         vm = new NoteViewModel(model, this);
     }
     return vm;
 }
 internal void RegisterViewModel(INote model, NoteViewModel vm)
 {
     if (noteViewModels.ContainsKey(model.ID) == false)
         noteViewModels.Add(model.ID, vm);
 }