用FeatureFactory 创建的图元是独立图元，这种图元怎么更新啊？例如改变他的位置。望高手赐教部分代码如下：
CMapXFeatureFactory cFactory=m_ctrlMapX.GetFeatureFactory();
CMapXFeature feature=cFactory.CreateSymbol(vtPoint,vtstyle); layer.AddFeature(feature);
不能用feature.Update();
