private bool CheckRemovable(Collection <CategoryVM> categories) { List <CategoryVM> usedCategories = new List <CategoryVM>(); foreach (CategoryVM category in categories) { if (StudyUnit.ContainsCodeByCategoryId(category.Id)) { usedCategories.Add(category); } } if (usedCategories.Count > 0) { string msg = EDOUtils.CannotDeleteError <CategoryVM>(Resources.Code, usedCategories, param => param.Title); MessageBox.Show(msg); return(false); } return(true); }