public MaterialManageViewModel(BaseViewModel parent)
        {
            this.parent = parent;

            // Get the list of all active materials
            materialList = MaterialModel.getMaterialList();
            // Get list of all deleted materials
            deletedMaterialList = MaterialModel.getDeletedMaterialList();

            // Keep a copy of the materialList so that we can restore the list after filtering
            originalMaterialList = new ObservableCollection <MaterialModel>(materialList);
        }