I have a sample program which does nothing but Hello World. I open IE and go to my development environement and access the silverlight, it loads the XAP first time and then if I close IE and open again, XAP does not get downloaded. Since there are no changes I expect it not to download.
After deploying it in QA environement, I open IE for the first time, it load XAP as expected. Now close IE and open again, I expect it not to download XAP but it does download XAP again. But if I would do refresh on the page it does not download XAp. So this happens only on Fresh IE open in our QA environment.
All the above tests are done on the same box with same IE setting. So there is no client side IE cache issue. I did check the date and Time on the servers to see if there is any difference as specified in silverlight XAP gets downloaded everytime link and our servers are in same date and time.
Does any one know how to prevent IIS not to download everytime?
The default settings in IE mean that a fresh instance of IE will always attempt to fetch each unique URL when it is first encountered. IE does this even if the cache headers sent with the resource the last time it was fetched would indicate the resource is still fresh.
However IE will send If-Modified-Since and/or If-None-Match when it re-requests a resource that it has a copy of in its cache. Hence the server has the option of responding with 304 Not Modified, are you sure that is not happening? The 304 has no entity body and is therefore a cheap response.
Note also that IE can make some strange heuristic choices if the server fails to send any cache control headers with a resource. One of these choices is where the resource is quite large no caching is performed.
If you haven't already done so I would recommend you set some reasonable Expiration on the ClientBin folder in IIS Manager (in IIS7 select the ClientBin folder, select "HTTP Response Header", open "Set Common Headers..", enable Expire Web content.