Overview of IlvMapFeatureIterator
A map feature iterator has three main methods:
The
IlvMapFeatureIterator::getNextFeature method allows you to iterate a stream of cartographic objects read from a file or queried from a database or a map server. It returns a null pointer when the last map feature has been read. The Rogue Wave Views predefined readers, which implement the
IlvMapFeatureIterator abstract class, always return the same instance of
IlvMapFeature. This means that each time the
getNextFeature method is called, the newly read map feature overwrites the previous one, which is permanently lost along with its geometry and attributes. As a consequence, you must be sure to use this map feature before invoking the
getNextFeature method again, or make a copy of the map feature if you wish to keep it. This is what we did in the example given in
Attaching Attributes to Graphic Objects.
The reason why map features have been made volatile is to avoid the situation where memory is allocated each time a new feature is read, thus resulting in a loss of performance. It is more efficient to allocate memory for storing a map feature when it is read for the first time and then update it only when necessary.
The
getDefaultFeatureRenderer method returns a renderer that is appropriate for each of the map features read. See
Renderers.
The following code example loads all the map features read by an iterator and puts them into a manager.
IlvFeatureRenderer* renderer = featureIterator->getDefaultFeatureRenderer(display); for (const IlvMapFeature* feature = featureIterator->getNextFeature(status); feature; feature = featureIterator->getNextFeature(status)) { if (status != IlvMaps::NoError()) { IlvPrint(IlvMaps::GetErrorMessage(status, display)); return; } IlvGraphic* graphic = renderer->makeGraphic(feature, mapinfo, status); if(graphic) manager->addObject(graphic, IlvFalse, layerIndex); else if(status != IlvMaps::NoError()) IlvPrint(IlvMaps::GetErrorMessage(status, display)); } |
Version 6.1
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