hi , i have written a simple Trigger on FeedItem when i am Creating a new record on custom object,  a new Item feed been created :" admin created this case." and the Trigger i wrote is not fired , why ???

Thanks .

hi , i have written a simple Trigger on FeedItem when i am Creating a new record on custom object,  a new Item feed been created :" admin created this case." and the Trigger i wrote is not fired , why ???

Thanks .