how can i update my avtar in xmpp using iphone SDK?

how can i update my avtar - login user avtar (photo) in xmpp using iphone SDK (XMPPStream) ?

i have XMPPvCardAvatarModule (but not having method description) 开发者_高级运维so not able to get how to use its methods to update avtar(image) ?? Can any one post sample code & links to understand that, i am stuck with this problem !! Thanks.

Most folks use XEP-153 for avatars. But please be careful implementing this. If you get your hash logic wrong, and you don't do negative caching, it wreaks havoc on the network as your client constantly re-queries for vcards that will never match the hash they're given. Please do NOT set your client to send vcard queries to everyone on your roster every time you log in -- please heed the MUST in the XEP for caching avatars, or do NOT implement this feature.

Also, please be aware the community hopes to one day move to XEP-84, which has the potential to be more efficient in certain cases.