For Linda and others who may need this:


I solved it and forget to put answer back  dont expect complete source code you need to study in order to get improve

add sth here:

class MCameraObserver
   {
   virtual void   PictureTaken() = 0;
   virtual void   SnapPreview() = 0;
   virtual void   Snap() =0;...

and correspondingly :

void CAppView::Snap()
    {
    ASSERT(iCameraManager != NULL);
    iCameraManager->Snap(*iBitmap);
    }

void CAppView::SnapPreview()
    {
    ASSERT(iCameraManager != NULL);
    iCameraManager->SnapLow(*iBitmap);
    }


Key changes here:
void CCameraManager::RunL()
   {
    if (iStatus != KErrNone)
        {
            iObserver.Error(iStatus.Int());
            return;
        }

    switch (iCameraState)
        {
    case EStartingCamera:
        iCameraServer.SetLightingConditions(RCameraServ::ELightingNormal);
              iCameraServer.SetImageQuality(RCameraServ::EQualityLow);
        iCameraState = EReady;
      iObserver.SnapPreview();//start preview from begining
      
        break;

   case EDisplayVideo:
      iObserver.PictureTaken();
      iCameraState = EReady;
      iObserver.SnapPreview();

      if(IsSnap) iCameraState = ETakingPicture;
         
      break;
    case ETakingPicture:

      
        iObserver.Snap();//maybe not show!
              iCameraState = EReady;
      
      
        break;

    case EReady:
      iObserver.PictureTaken();
      
      break;
      
    case EError:
    default:
        iCameraState = EError;  //  For the invalid cases
        iObserver.Error(KErrGeneral);

        }
   }


You need to chage this part according to your application:
void CCameraManager::ConstructL()
   {
    User::LeaveIfError(iCameraServer.Connect());

    iCameraState = EStartingCamera;
    iCameraServer.TurnCameraOn(iStatus);

   CActiveScheduler::Add(this);

   SetActive();
   IsSnap = EFalse;
   }


TBool CCameraManager::IsReady()
    {
    if (iCameraState == EReady)/// otherwise it does not draw!
        {
        return  ETrue;
        }
    else
        {
        return  EFalse;
        }
    }

TBool CCameraManager::IsPreview()
    {
    if (iCameraState == EDisplayVideo)/// otherwise it does not draw!
        {
        return  ETrue;
        }
    else
        {
        return  EFalse;
        }
    }

void CCameraManager::Snap(CFbsBitmap& aBitmap)
    {
   //iCameraServer.SetImageQuality(RCameraServ::EQualityHigh);// use low quality first
    iCameraServer.GetImage(iStatus, aBitmap);
    SetActive();
    }
////////////////////////////////////////////////////////////////

void CCameraManager::SnapLow(CFbsBitmap& aBitmap)
{
   ASSERT(IsReady());// must be ready then call it! the it is not EReady anymore but EDisplayvideo
   iCameraState=EDisplayVideo;
   iCameraServer.SetImageQuality(RCameraServ::EQualityLow);
   iCameraServer.GetImage(iStatus,aBitmap);
   SetActive();

}


Anything more?.... oh this must be added:
void CAppView::Draw(const TRect& /*aRect*/) const
    {
   TBool DugMsg = ETrue;

    ASSERT(iCameraManager != NULL);

    // Clear the screen
    CWindowGc& gc = SystemGc();
   gc.UseFont(NEikonEnvironment::EikEnv().AnnotationFont());


    gc.Clear(Rect());
   if ( (iCameraManager->IsReady()||iCameraManager->IsPreview()) && (iBitmap->Handle()) )///add preview option otherwise it does not draw!
      {
   //   gc.DrawBitmap(Rect(), iBitmap, iBitmap->SizeInPixels());//this produce flicking effect.
      gc.BitBlt(TPoint(8,10), iBitmap);/// this does not produce flicking effect

In somewhere of the posted problem this flickring proble was mentioned and here is the solution...

TBool IsSnap is in CCameraManager...

Did I already give the complete code? if you miss anything that's the part you need to study and pls be kind enough to add some more line for others when you success, it has been half year and I can obviously miss something...

Good luck Linda