in iOS 7 there is no problem for this method:
_rootViewController.modalPresentationStyle = UIModalPresentationCurrentContext;
[_rootViewController presentViewController:self animated:NO completion:nil];
But in iOS 8 it did nothing.How to solve it? Is it a Bug for iOS 8?
My answer is more simple, below code. This works in iOS8 (XCode6 GM seed).
HogeViewController *vc = [[HogeViewController alloc] init];
vc.modalPresentationStyle = UIModalPresentationOverFullScreen;
[self presentViewController:vc animated:NO completion:nil];