[GIS] Using OpenLayers Script protocol callback

openlayers-2

I have a layer with a BBOX strategy with a script protocol to get the data from our server. I'd like make use of the callback function http://dev.openlayers.org/docs/files/OpenLayers/Protocol/Script-js.html#OpenLayers.Protocol.Script.callback
to intercept the server response and modify it based on the current state of the map (due to user interactions)
If I understand it correctly, that function should get the 'raw' response of the server. But for now it just doesn't do anything:

this.layer = new OpenLayers.Layer.Vector("POI",{
        strategies: [
            new OpenLayers.Strategy.BBOX({
                resFactor: 2,
                active: false,
                autoActivate: false,
                ratio: 1.3,
                noAbort: true
            }), 
            new OpenLayers.Strategy.Cluster({
                distance: this.clusterDistance,
                threshold: this.clusterThreshold
            })
        ],
        protocol: new OpenLayers.Protocol.Script({
            url: 'http://localhost/tests/poi',
            callback: tbPoi.myOwnCallback,
            callbackKey: 'callback',
            format: new OpenLayers.Format.GeoJSON(in_options),
            params: {
                poi: tbPoi.getPoi,
                geozone: tbPoi.getGeozone
            }
        }),
        styleMap: new OpenLayers.StyleMap({
            "default": style,
            "vertex": tbMap.vertexStyle
        }, {extendDefault: false})
    });

myOwnCallback: function(data){
    console.log(data);
},

The myOwnCallback function is completely ignored. I have no idea how to make this work. I searched for examples but couldn't find one.

I want this function to test if individual features returned by the server are also on my drawing layer (if a user is modifying one) So I don't get duplicates on the map.

Best Answer

OK, I've figured this out. You can use the option: parseFeatures in the protocol:

protocol: new OpenLayers.Protocol.Script({
        url: 'http://localhost/tests/poi',
        callback: tbPoi.myOwnCallback,
        callbackKey: 'callback',
        format: new OpenLayers.Format.GeoJSON(in_options),
        parseFeatures: myOwnCallback,
        params: {
            poi: tbPoi.getPoi,
            geozone: tbPoi.getGeozone
        }
}),

The myOwnCallback function should use the formatter to give the correct return.

myOwnCallback: function(data) {
    return this.format.read(data);
},

The data it receives is the GeoJSON object as returned by the server. So in the function you can deconstruct and change it any way you like. I've made a new array with the features that are not on the drawing layer and put that back as the feature part of the data object.

data.features = temp;

works great.

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