PageLayout键盘移动选中元素怎么实现？

IHookHelper hookHelper = new HookHelperClass();
hookHelper.Hook = axPageLayoutControlMain.Object;

IGraphicsContainerSelect graphicsContainerSelect = hookHelper.ActiveView as IGraphicsContainerSelect;
 
IElement element = graphicsContainerSelect.SelectedElement(i);
ESRI.ArcGIS.Geometry.IEnvelope envelope = element.Geometry.Envelope;
envelope.Offset(15, 0);
 
直接更改坐标并没有卵用，请大神救火~感谢