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Map Feature Attributes
Each map feature can also have attributes. If the map feature is a town, its attributes can be its name, or the number of inhabitants. Attributes can be used, for example, for graphical rendering. In the section Creating a Colored Line Renderer the color of polylines representing contour lines on a map is defined by the elevation attribute.
Attributes belong to the class IlvFeatureAttribute. They are stored in the following two classes:
*IlvFeatureAttributeInfo, which defines the attribute properties, such as name, type, mandatory, or optional characters.
*IlvFeatureAttributeProperty, which contains the values of these attributes.
The following code sample lists the attributes of an IlvMapFeature object and displays them on the screen.
void
dumpAttributes(const IlvMapFeature* feature)
{
const IlvFeatureAttributeProperty* attributes =
feature->getAttributes();
if(!attributes)
return;
const IlvFeatureAttributeInfo* info =
attributes->getInfo();
if(info) {
IlvUInt count;
count = info->getAttributesCount();
for(IlvUInt i = 0; i < count; i++) {
 
const char* name = info->getAttributeName(i);
 
const IlvMapClassInfo* clsinfo = info->getAttributeClass(i);
const IlvFeatureAttribute* fa = attributes->getAttribute(i);
if(clsinfo->isSubtypeOf(IlvStringAttribute::ClassInfo())) {
const char *str = ((IlvStringAttribute*)fa)->getValue();
IlvPrint(“%s %s”, name ? name : “”, str ? str : “”);
} else if(clsinfo->isSubtypeOf(IlvIntegerAttribute::ClassInfo())){
int in = ((IlvIntegerAttribute*)fa)->getValue();
IlvPrint(“%s %d”, name ? name : “”, in);
} else if(clsinfo->isSubtypeOf(IlvDoubleAttribute::ClassInfo())){
double dbl = ((IlvDoubleAttribute*)fa)->getValue();
IlvPrint(“%s %g”, name ? name : “”, dbl);
} else if(clsinfo->isSubtypeOf(IlvBooleanAttribute::ClassInfo())){
IlvBoolean bo = ((IlvBooleanAttribute*)fa)->getValue();
IlvPrint(“%s %s”, name ? name : “”,
bo ? “true” : “false”);
}
}
}
}
 
The attributes are of different types, according to whether they represent whole numbers, floating-point values, character strings, and so on. The predefined attributes, all of the IlvFeatureAttribute class, are in the attribute package.

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