图层附加材质疑问

根据郭老师之前相关帖子的回复，如下代码  但是执行图层SetOverrideMaterial 返回值为False

var levelCache = Session.Instance.GetActiveDgnModel().GetFileLevelCache();
                var handles  = levelCache.GetHandles();
                EditLevelHandle newLevel;
                if (handles.Contains(t => t.Name == LevelName))
                {
                    var temp = levelCache.GetLevelByName(LevelName);
                    newLevel = temp.GetEditHandle();
                }
                else
                {
                    newLevel = levelCache.CreateLevel(LevelName);
                }
                //设置图层颜色
                newLevel.SetByLevelColor(new LevelDefinitionColor(color.To_Uint(), Session.Instance.GetActiveDgnModel().GetDgnFile()));
                var materialId = new MaterialId("Concrete_3");
                var result = newLevel.SetOverrideMaterial(new LevelDefinitionMaterial(materialId.ElementId, Session.Instance.GetActiveDgnModel().GetDgnFile()));
                levelCache.Write();

其中LevelName 为新建图层名称，可替换任意字符串

若图层材质设置成功之后，请问一下老师，这个属性对应的API是？