Avoid browser caching with Flash/Flash builder with the random number trick

A simple way to avoid caching of static files that get replaced sometimes is by appending a ?r=randomNumber to the filename. For webservers everything behind the ? are dynamic parameters using the format variable1=value1&variable2=value2… and so on. As long as you don’t handle those parameters in your scripts they get ignored by the server. The browser on the other hand thinks that the parameter changes the content thus asks for the new data from the server instead of grabbing existing content from the cache.

var filename:String="somefile.xml?r="+(Math.random()*99999999999);

While this works online it won’t work when you test locally inside the Flash IDE. Why? Simple. The file system is not a webserver thus interpretes the parameters as part of the filename. Since we don’t want this to happen when testing in the IDE and it’s prone to cause errors on the long run if you out comment that line during tests you need to find a way to only add the random parameter when not testing locally. Here’s the way to do it:

var filename:String="somefile.xml";
if(root.loaderInfo.loaderURL.substr(0,5)!="file:"){
	xmlFile+="?"+(Math.random()*99999999999);
}

In Actionscript 2 you had _root._url and in Actionscript 3 you got “root.loaderInfo.loaderURL” where root of course needs to be available in the local context, eg if you run the script on the time line or in an instance of the MovieClip class. “root.loaderInfo.loaderURL” contains the URL where the SWF file has been loaded from. In case of local testing this is something like “file:///d:/testfolder/test.swf” and in case of the file being online it’s something like “http://notboring.org/test.swf”. Thus you only need to check for the first characters of the URL and you know if you execute the file locally or from a HTTP server.

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