Open Cascade：如何从AIS_Shape导出TopoDS_Shape？

if( !myAISContext->HasOpenedContext())
{
wxMessageBox(_T("It is necessary to activate the edges selection mode\n\and select edges on an object before \nrunning this function"),_T("Error!"));
return;
}

myAISContext->InitSelected();
if (myAISContext->MoreSelected()) {
Handle(AIS_Shape) S = Handle(AIS_Shape)::DownCast(myAISContext->SelectedInteractive());

if (S.IsNull()){
wxMessageBox(_T("It is necessary to activate the edges selection mode\n\and select edges on an object before \nrunning this function"),_T("Error!"));
return;
}

TopoDS_Shape Sh=S->Shape();