How would I go about auto populating a UISearch field with data from a JSON web feed

How would I go about auto populating a UISearch field with data from a
JSON web feed

How would I go about auto populating a UISearchBar field with data from a
JSON web feed? I have access to a list of cities via a JSON feed and would
like to display them in the UISearchBar field so that if the user starts
typing "San..." then San Diego auto completes for them. It would change if
"San F.." was entered and auto display "San Francisco" etc...
I'm dealing with city names and don't want the user to misspell a city and
get no results because of it.
thanks for any help