public ViewModel() { SelectedColor = new ColorModel(); PropertyChanged += (sender, args) => { if (args.PropertyName == nameof(SelectedColor)) { deleteColorCommand.RaiseCanExecuteChanged(); addColorCommand.RaiseCanExecuteChanged(); } }; addColorCommand = new DelegateCommand(AddSelectedColor, () => colors.Contains(SelectedColor) == false); deleteColorCommand = new DelegateCommand(RemoveSelectedColor /*, /*()=>colors.Contains(SelectedColor) == true*/); }