解决方法1：前面加上layoutIfNeeded
[self loadViewIfNeeded];
[self.collectionView scrollToItemAtIndexPath:[NSIndexPath indexPathForRow:self.currentIndex inSection:0] atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:NO];
解决方法2：viewDidLayoutSubviews
- (void)viewDidLayoutSubviews {
[super viewDidLayoutSubviews];
[self.collectionView scrollToItemAtIndexPath:[NSIndexPath indexPathForRow:self.currentIndex inSection:0] atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:NO];
}
