How to get notified when ever I select any frame (any page item) ?

Question

I have added a observer class in my plugin which derives from ActiveSelectionObserver.
But my observer constructor is not getting called when i select a page item. (In short, I am not getting notified about the selection)
below is my code:
class CSDTSelectionObserverImpl : public ActiveSelectionObserver
public:
  CSDTSelectionObserverImpl(IPMUnknown *boss);
   virtual ~CSDTSelectionObserverImpl();
protected:
   virtual void    HandleSelectionChanged (const ISelectionMessage*);
   virtual void HandleSelectionAttributeChanged(const ISelectionMessage* selectionMessage);
CREATE_PMINTERFACE(CSDTSelectionObserverImpl, kCSDTSelectionObserverImpl)
CSDTSelectionObserverImpl::CSDTSelectionObserverImpl(IPMUnknown *boss) : ActiveSelectionObserver(boss,IID_ICSDTSELECTIONOBSERVER) { }
CSDTSelectionObserverImpl::~CSDTSelectionObserverImpl() { }
void CSDTSelectionObserverImpl::HandleSelectionChanged(const ISelectionMessage* selectionMessage) { }
void CSDTSelectionObserverImpl::HandleSelectionAttributeChanged(const ISelectionMessage* selectionMessage) {  
if (selectionMessage && selectionMessage->WasSuiteAffected(IID_ILAYOUTSELECTION_ISUITE))
Also, In my .fr file, I have added below:
AddIn
  kDocBoss,
  kInvalidClass,
    IID_ICSDTSELECTIONOBSERVER, kCSDTSelectionObserverImpl,
Do I need to implement the ILayoutSelectionSuite as well to get the notification on page item selection or implementing Observer via ActiveSelectionObserver is sufficient?
Please help.

Answer 1

I tried below in debug mode , but it gave me error while execution (when the line of code was called by in-design)
InterfacePtr<ILayoutSelectionSuite> iLayoutSelectionSuite(fCurrentSelection, UseDefaultIID());
        if (iLayoutSelectionSuite == nil)
            break;
iLayoutSelectionSuite->SelectPageItems(selection,Selection::kReplace,Selection::kDontScrollLayoutSelection); // Error
So I was not able to get the UIDList of the selected page items, hence I used below code and this is working.
  InterfacePtr<const IIntegratorTarget> iIntegratorTarget(iLayoutSelectionSuite, UseDefaultIID());
        std::auto_ptr<IIntegratorTarget::TargetSuiteCollection> selectionSuites(iIntegratorTarget->GetTarget(ILayoutTarget::kDefaultIID));
        for(IIntegratorTarget::TargetSuiteCollection::size_type i = 0; i < selectionSuites->size(); i++)
            ILayoutTarget* target = (ILayoutTarget*)selectionSuites->at(i).get();
            if(!target)
                continue;
            selection = target->GetUIDList(kDontStripStandoffs);
But it would have been much easier and logical if I can get it using IlayoutSelectionSuite or if there is some better approach ?
Please let me know.
ileleLayoutSelectio
Let me