how to use GetSectionedBody() funtion

Hi All,

now, I'm studing about Solidwork API. this is my problem, if youcan, please answers for me
C#:

ModelDoc2 doc = (ModelDoc2)this.iSwApp.ActiveDoc;
ModelView view = (ModelView)modeDoc.ActiveView;
SelectionMgr selectMgr = (SelectionMgr)modeDoc.SelectionManager;

bool status = modeDoc.Extension.SelectByID2("???", "PLANE", 0, 0,0, true, 1, null, 0);

SectionViewData viewData =modeDoc.ModelViewManager.CreateSectionViewData();

Feature obj = (Feature)objSelectMgr.GetSelectedObject6(2, -1);

viewData.FirstPlane = (object)obj;
viewData.FirstOffset = 0.0;
viewData.FirstReverseDirection = false;
viewData.FirstRotationX = 0.0;
viewData.FirstRotationY = 0.0;
viewData.FirstColor = 255;
viewData.ShowSectionCap = true;

bool resutl =modeDoc.ModelViewManager.CreateSectionView(objViewData);
Body2 body = (Body2)doc.GetSectionedBody(view);

but why body object allways is null ?
SolidworksApi macros