[OpenLayers-Dev] redraw(true) and random HTTP GET parameter with XYZ Layer

[Andreas Hocevar]

Hi,

XYZ layers usually use cached tilesets where the server cache controls browser caching by using etags and/or appropriate cache header. So it should not be necessary to use a random param to invalidate the browser cache.

It seems you have access to the server or do something in your application that changes tiles on the server, and this is why you want a redraw on the client. If so, it should also be possible for you to use etags. If not, I'd suggest dealing with this on the application level, e.g. by changing the layer's url before the redraw.

Andreas.

On Nov 4, 2011, at 17:58 , JD wrote:

> Hi,
> I try to force redraw of a XYZ layer on timeout using the redraw(true)
> method on layer.
> 
> But it doesn't seems to do the trick, no random argument is added to
> HTTP GET tiles requests.
> 
> After some time looking code I modified XYZ class.
> http://trac.osgeo.org/openlayers/browser/trunk/openlayers/lib/OpenLayers/Layer/XYZ.js
> 
>> From :
> 129	    getURL: function (bounds) {
> 130	        var xyz = this.getXYZ(bounds);
> 131	        var url = this.url;
> 132	        if (OpenLayers.Util.isArray(url)) {
> 133	            var s = '' + xyz.x + xyz.y + xyz.z;
> 134	            url = this.selectUrl(s, url);
> 135	        }
> 136	
> 137	        return OpenLayers.String.format(url, xyz);
> 138	    },
> 
> To :
> 129	    getURL: function (bounds) {
> 130	        var xyz = this.getXYZ(bounds);
> 131	        var url = this.getFullRequestString();
> 132	        if (OpenLayers.Util.isArray(url)) {
> 133	            var s = '' + xyz.x + xyz.y + xyz.z;
> 134	            url = this.selectUrl(s, url);
> 135	        }
> 136	
> 137	        return OpenLayers.String.format(url, xyz);
> 138	    },
> 
> It seems that random parameter added to class this.params are only
> used by HTTPRequest::getFullRequestString and ignored by XYZ::getURL.
> After some tests this modification seems to work fine.
> 
> Can you tell me if this is a genuine bug or I simply use the
> OpenLayers API incorrectly ?
> 
> Thanks,
> JD.
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-- 
Andreas Hocevar
OpenGeo - http://opengeo.org/
Expert service straight from the developers.