Map attribute filters

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A IlvMapAttributeFilter object is used to compute the value of a styling attribute from a value found in an IlvGraphic instance. Typically, this value is retrieved from the IlvFeatureAttributeProperty named property attached to a IlvGraphic object. To install such a filter, you set it to an IlvMapStyle object.

The following example shows a custom filter class that defines the foreground of map graphic objects according to their “VALUE” feature attribute.

/**
 * Computes the foreground from a graphic's IlvFeatureAttribute
*/
class ColorAttributeFilter implements IlvMapAttributeFilter {
  /**
   * Method that returns the new color computed from the "VALUE" 
   * feature attribute. If DEFAULT_VALUE is returned, the style value on which 
   * the filter is installed will not be affected.
   */
  public Object get(IlvGraphic g, String attributeName) {
    if(IlvPolylineStyle.FOREGROUND.equals(attributeName)) {
     IlvAttributeProperty p = (IlvAttributeProperty) 
       g.getNamedProperty(IlvAttributeProperty.NAME);
     if(p == null)
       return DEFAULT_VALUE;
     Object o = p.getValue("VALUE");
     Object ret = convertObjectToColor(o);
     if(ret == null)
       return DEFAULT_VALUE;
     return ret;
   }
}

The following code example shows how to install a custom filter class in a map layer style.

 IlvMapAttributeFilter filter = new ColorAttributeFilter();
 IlvMapLayer layer = getLayer();
 IlvMapStyle style = layer.getStyle();
 style.setAttributeFilter(filter);

Once the filter is installed, each request to retrieve an attribute value is passed to the get method of the filter.

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Map layers and map styles