Query-string in SWF URL is bad idea because swf would be downloaded again by browser/client instead of being loaded from browser-cache, it happens if URL becomes non-unique due to the presence of changing query-string in different requests.
Browser does cache data for all URL, unless HTTP response headers (for URL or other resources) instruct not to do caching. If URL is different, browser considers it a new requests and downloads the data again instead of consuming from cache.
We can try to avoid or optimize such cases. In past, developers have used the other way by having random (non-unique) query-string in SWF or XML/asset URL to force reloading of asset/resource instead of using the ones from browser-cache. Though, they could have done things by setting right HTTP headers.
I have noticed some websites where swf URL has a query-string i.e. http://yoursite.com/yourapp.swf?var1=somedata, where value of var1 is not constant rather changes? Obvious reason, I want to pass dynamic data most of time hence using query-string instead of hard-coding it in swf itself.
I also noticed some sites which are using SWFObject and still passing data via query-string instead of flashvars using addVariable (..) instance method of SWFObject.
Another place, I again noticed something similar, AVM+ application loads AVM- (SWF 8 or less) application, let’s call it legacy-swf, and passes data via query-string, ok, that is understood there is no other way except writing a light-weight wrapper that uses LocalConnection or query-string approach?
- It might not be worth writing wrapper in case of small-size legacy-swf but depends, if you are serving to thousands of users, every single HTTP request cost something.
- If legacy-swf is large enough, it’s worth writing a wrapper that loads the legacy-swf. This way at least legacy-swf would be loaded from browser cache in next session instead of being downloaded again from your server.
This is very basic thing in web-application development, user-experience can be improved by doing these little things. I hope to write some more observations, no matter how stupid/trivial it sounds to me or other programmers. It’s good to post these things in context of flash/flex so beginners, who are not familiar with details of HTTP or other standards, can learn.