FBFriendPickerViewController with FBCacheDescriptor - limited friends list
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I would like to present a limited list of friends (e.g. generated by a specific FQL) using [FBFriendsPickerViewController](https://developers.facebook.com/docs/sdk-reference/iossdk/3.0/class/FBFriendPickerViewController/). The documentation hints that the friends list can be pre-fetched using [FBCacheDescriptor](https://developers.facebook.com/docs/sdk-reference/iossdk/3.0/class/FBCacheDescriptor/), but the documentation of the latter is poor. I didn't find any example in the SDK samples.