ASP.Net Caching

We can easily cache data in asp.net using the Caching class provided by asp.net

Here is an example of how to cache data.

if(Cache["data"]==null)
{
Cache.Insert("data", data, null, System.Web.Caching.Cache.NoAbsoluteExpiration, System.Web.Caching.Cache.NoSlidingExpiration);
}

This will cache the "data" until it is removed from the memory.

So how can we know when the cached data is being removed from the memory?

ASP.Net provides a cool feature, that enables us to do it.

There is a delegate to achieve this
System.Web.Caching.CacheItemRemovedCallback
which has the following signature

void RemoveCacheItemHandler(string key, Object value, CacheItemRemovedReason reason);

This delegate can be used to get notification once a particular cached item being removed.

Example of how we can use the delegate:

if(Cache["data"]==null)
{
Cache.Insert("data", data, null, System.Web.Caching.Cache.NoAbsoluteExpiration, System.Web.Caching.Cache.NoSlidingExpiration, RemoveCacheItemHandler);
}

public void RemovedCacheItemHandler(string key, Object value, CacheItemRemovedReason reason)
{
switch (key)
{
case "data":
// cache has been removed; do the process
break;
}
}