Sample codes in C++ Builder to update coordinates at GoogleMapPolyElementEditEnd event.

Hi,
I have asked how to update coordinates at the GoogleMapPolyElementEditEnd event and got sample codes in Delphi. When I put the codes in C++ Builder, it kept saying "E2316 'JSON' is not a member of 'TTMSFNCMapsCoordinates'".

Here are my codes:
if (AEventData->PolyElement) {
TheGoogleMap->BeginUpdate();
UnicodeString ClassName=AEventData->PolyElement->ClassName();
if (ClassName==u"TTMSFNCGoogleMapsPolygon") {
TTMSFNCGoogleMapsPolygon* PolygonPtr= (TTMSFNCGoogleMapsPolygon*) AEventData->PolyElement;
PolygonPtr->Coordinates->JSON = AEventData->CustomData;
} else if (ClassName==u"TTMSFNCGoogleMapsPolyline") {
TTMSFNCGoogleMapsPolyline* PolygonPtr= (TTMSFNCGoogleMapsPolyline*) AEventData->PolyElement;
PolygonPtr->Coordinates->JSON = AEventData->CustomData;
}
TheGoogleMap->EndUpdate();
}

Can someone help me point out what I did wrong and how to get the editted coordinates?
Thanks!