ios - What does it mean when a view is not in the window hierarchy? -

okay, i've tried implement delegate method on uiimagepickercontroller stated @michaelking in previous post of mine.

- (void)imagepickercontroller:(uiimagepickercontroller *)picker didfinishpickingmediawithinfo:(nsdictionary *)info { [picker dismissviewcontrolleranimated:false completion:nil]; image = [info objectforkey:@"uiimagepickercontrolleroriginalimage"]; } 

however, following error in code: warning: attempt present <uiimagepickercontroller: 0xc464f10> on <rpflipsideviewcontroller: 0xc66a270> view not in window hierarchy!

i don't understand means, , searching online, haven't found i've been able understand. can please clarify? maybe still don't understand whole delegate thing?

here previous post, reference: how reference picture took in ios?

the view controller's view must on screen (not visible) must in hierarchy somewhere. without being in current view hierarchy there no graphics context in present picker.