There appears to be no way of setting frictionless requests as on for facebook ios sdk. For Javascript inplementations this can be done in the fb.init method.
The on
This call enables frictionless requests:
[facebook enableFrictionlessRequests];
But it is not enough to prevent all dialogs from appearing briefly. Since the frictionless recipient cache is by default not loaded until the first dialog appears. Once the first dialog appears, the frictionless recipient list will be loaded and subsequent dialogs won't appear. However, you can call
[facebook reloadFrictionlessRecipientCache];
after a successful login to have the frictionless recipient cache ready before the first dialog appears.
Franco