Most programmers use the ViewState to preserve data across postbacks and the Session to preserve data for a user. There are cases when you want to preserve data across users. Maybe you are using an IHttpHandler and you want to send information through a key between your application and the handler. Or maybe you want to keep data that is resource consuming to acquire, but used by more users of the same application. Here is where Cache comes along.

There are two things you need to pay attention to when you are using the Cache:
  • While using the syntax Cache[key] is very simple and consistent with the ViewState, Session or other dictionaries you are used to, you need to be aware that in case of the server freeing memory, the cache items will be removed based on priority. Try to use Cache.Add or Cache.Insert with CacheItemPriority.NotRemovable when you are sure you don't want this to happen. The Absolute and Sliding expirations will still work.
  • I've read somewhere that HttpContext.Current.Cache does not work across users. It's like another Session object. Use HttpRuntime.Cache instead. I also looked in the ASP.Net source code and I found out that HttpContext.Cache returns HttpRuntime.Cache, so I don't see how these two properties could behave any differently. HttpRuntime is much easily usable, though, since it works in situations where HttpContext.Current is null


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