解決方法1：前面加上layoutIfNeeded

[self loadViewIfNeeded];

[self.collectionView scrollToItemAtIndexPath:[NSIndexPath indexPathForRow:self.currentIndex inSection:0] atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:NO];

解決方法2：viewDidLayoutSubviews

- (void)viewDidLayoutSubviews {

[super viewDidLayoutSubviews];

[self.collectionView scrollToItemAtIndexPath:[NSIndexPath indexPathForRow:self.currentIndex inSection:0] atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:NO];

}