[OpenLayers-Users] How to know if a WFS layer has no features?

[Tim Schaub]

Guido_bs wrote:
> Hello, I'm not so good in using OL, so I have a question for you experts.
> In my application I build a WFS layer and this layer can have some WFS
> features (shown as markers) or not, it depends from a query to Mapserver:
> 
> layer_wfs = new OpenLayers.Layer.WFS( "My Markers", MAPSERVER_URL,
> {map:MAPFILE_DIR+filtercode+".map", typename: "filter"},{ featureClass:
> OpenLayers.Feature.WFS});
> 
> If there are not features for the layer, Mapserver gives me this answer:
> 
> <?xml version='1.0' encoding="ISO-8859-1" ?>
> 
> <wfs:FeatureCollection
> 
>    xmlns:MYSQL="http://ogc.dmsolutions.ca/gml/2.1.2/feature.xsd"
> 
>    xmlns:wfs="http://www.opengis.net/wfs"
> 
>    xmlns:gml="http://www.opengis.net/gml"
> 
>    xmlns:ogc="http://www.opengis.net/ogc"
> 
>    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
> 
>    xsi:schemaLocation="http://www.opengis.net/wfs
> http://schemas.opengeospatial.net/wfs/1.0.0/WFS-basic.xsd 
> 
>                        http://ogc.dmsolutions.ca/gml/2.1.2/feature.xsd
> http://foo.foo.org/cgi-bin/mapserv
> 
> ?SERVICE=WFS&amp;VERSION=1.0.0&amp;REQUEST=DescribeFeatureType&amp;TYPENAME=filter&amp;OUTPUTFORMAT=XMLSCHEMA">
> 
>    <gml:boundedBy>
> 
>       <gml:null>missing</gml:null>
> 
>    </gml:boundedBy>
> 
> </wfs:FeatureCollection> 
> 
> I'd like to know if after its creation, layer_wfs has no WFS features. Is
> there a function in OL to do it? I thought to read the "missing" string in
> Mapserver answer but I don't know how to do it and I don't understand where
> Mapserver answer is read by OL. 
> My OL version is 2.5.
> Thanks a lot,
> Guido

If your layer has no features, then:

layer_wfs.features.length == 0;

Since your data is loaded asynchronously, you'd have to listen for the 
"loadend" event on your layer:

layer_wfs.events.register("loadend", layer_wfs, function() {
     if(this.features.length == 0) {
         // do something about no features
     }
});

or something like that.

Tim