Display attributes of feature with clustering

Question

I have one KML layer that has roughly 900 features and I added OpenLayer.Cluster.Strategy to help the layer display a little quicker.

My KML displays the attributes when clicked on before clustering was enabled, but now the bubble displays 'undefined, undefined'.

How did the clustering change the extractAttributes property?

            var state = new OpenLayers.Layer.Vector("State Probation", {
            projection: map.displayProjection,
            strategies: [new OpenLayers.Strategy.Fixed(), new OpenLayers.Strategy.Cluster()],
            protocol: new OpenLayers.Protocol.HTTP({
                url: "state.kml",
                format: new OpenLayers.Format.KML({
                    extractStyles: true,
                    extractAttributes: true
                })
            })
        });


        select = new OpenLayers.Control.SelectFeature([sample, state],
            {
                clickout: true, toggle: false,
                multiple: true, hover: false,
                toggleKey: "ctrlKey", // ctrl key removes from selection
                multipleKey: "shiftKey" // shift key adds to selection
            });

        sample.events.on({
            "featureselected": onFeatureSelect,
            "featureunselected": onFeatureUnselect
        });

        state.events.on({
            "featureselected": onFeatureSelect,
            "featureunselected": onFeatureUnselect
        });

        map.addControl(select);
        select.activate();   

        map.addControl(new OpenLayers.Control.LayerSwitcher());



    function onPopupClose(evt) {
        select.unselectAll();
    }

    function onFeatureSelect(event) {
        var feature = event.feature;
        var selectedFeature = feature;
        var popup = new OpenLayers.Popup.FramedCloud("chicken", 
            feature.geometry.getBounds().getCenterLonLat(),
            new OpenLayers.Size(100,100),
            "<h2>"+feature.attributes.name + "</h2>" + feature.attributes.description,
            null, true, onPopupClose
        );
        feature.popup = popup;
        map.addPopup(popup);
    }
    function onFeatureUnselect(event) {
        var feature = event.feature;
        if(feature.popup) {
            map.removePopup(feature.popup);
            feature.popup.destroy();
            delete feature.popup;
        }
    }

Answer 1

When working with clusters, OpenLayers creates an array of attributes to store the attributes of all features in the cluster. When your points are in a cluster you need to access the array instead of the attribute directly. Example (untested):

function onFeatureSelect(event) {
    var feature = event.feature;
    var selectedFeature = feature;
    var text = ""
    if(feature.cluster) {
        for(var i=0; i<feature.cluster.length; i++) {
            text += "<h2>"+feature.cluster[i].attributes.name + "</h2>" + 
                   feature.cluster[i].attributes.description + "\n";
        }
    } else {
        text = "<h2>"+feature.attributes.name + "</h2>" + feature.attributes.description;
    }

    var popup = new OpenLayers.Popup.FramedCloud("chicken", 
        feature.geometry.getBounds().getCenterLonLat(),
        new OpenLayers.Size(100,100),
        text,
        null, true, onPopupClose
    );
    feature.popup = popup;
    map.addPopup(popup);
}

Answer 2

this works for me:

function onFeatureSelect(event) {
    var feature = event.feature;
    var layerName = event.feature.layer.name;
    var content = "unInitialized";
    // alert ('selected this feature='+feature.id+ '<br/>Atributos: '+feature.attributes.description);
    if ( (feature.attributes.name > '') || (feature.attributes.description > '') ) {
        content = feature.attributes.name + '<br/>'+feature.attributes.description;
    } else {
        if (feature.cluster) {
            content = feature.attributes.count + ' ' + layerName ;
            for (var i = 0; i < feature.attributes.count; i++) {
                    var feat = feature.cluster[i];
                    content += '<br/>'+feat.attributes.name;
            }
        } else {
            content = 'NOT a cluster either';
        }
    }

    popup = new OpenLayers.Popup.FramedCloud("chicken", 
                             feature.geometry.getBounds().getCenterLonLat(),
                             new OpenLayers.Size(100,100),
                             content,
                             null, true, onFeatureUnselect);
    popup.setBackgroundColor('white');
    feature.popup = popup;
    map.addPopup(popup);
    // GLOBAL variable, in case popup is destroyed by clicking CLOSE box
    lastfeature = feature;
    // alert ('select'+lastfeature.name);
}