collectionview scrollToItemAtIndexPath不使用分页

Question

//Scroll to top
NSIndexPath *index=[NSIndexPath indexPathForRow:0 inSection:0];
[self.collectionview scrollToItemAtIndexPath:index atScrollPosition:UICollectionViewScrollPositionBottom animated:YES];

我尝试了这段代码，但它无效

[self.collectionview setContentOffset:CGPointMake(0,250) animated:YES];

使用此代码也只有相同的结果