BizObject PrugeCacheItems method

alfinmass · August 7th, 2009, 04:59 PM

Hi,

I don't know if this question has been posted before, but I couldn't find it. I am looking at the

Code:

BizObject.PurgeCacheItems()

static method (page 108 of the book) and I am wondering if there is any way to avoid using two loops to do a task.

The first loop (the while loop) fills a list and then the second uses the list to purge the cache. I am thinking that using the enumerator we cannot remove the item directly in the while loop because that will set the enumerator out of sync with the elements in the dictionary. However, is there not another way to loop through the elements of the dictionary so that you can remove the elements in one single loop?

Thanks!

Lee Dumond · August 11th, 2009, 10:39 PM

According to MSDN (regarding the GetEnumerator method)

"Items can be added to or removed from the cache while this method is enumerating through the items."

If so, seems to me this would work:

Code:

protected static void PurgeCacheItems(string prefix)
{
   IDictionaryEnumerator enumerator = Cache.GetEnumerator();
   while (enumerator.MoveNext())
   {
      if (enumerator.Key.ToString().ToLower().StartsWith(prefix.ToLower()))
      {
         Cache.Remove(enumerator.Key.ToString());
      }               
   }
}

However, like you said, it was always my understanding that deleting elements from a collection invalidates the enumerator, in which case an InvalidOperationException would be thrown. Hmm... have to try it now...

EDIT: Just tried it. seems to work fine.

alfinmass · August 12th, 2009, 08:16 AM

Thanks Lee, that was exactly the code I thought of first, and then somehow I thought it wouldn't work because as it iterates forward it would lose it's 'counting'. My next thought was if there was a way to iterate backwards (starting at the last item and finishing in the first) through the cache, because that way if you remove an item of the collection you would not lose your 'count'.

Thanks again!