轻按时如何将 UICollectionView 居中? [英] How to center a UICollectionView when it is tapped?

问题描述

我有一个 UICollectionView，上面有很多 UICollectionViewCells.我想在点击时将单元格滚动到 UICollectionView 的中心.我担心的是，即使我点击最后一个或顶部的单元格，它也应该移动到集合视图的中心.

I have a UICollectionView and it has quite a lot of UICollectionViewCells on it. I want to scroll the cell to the centre of the UICollectionView when it is tapped. My concern is that even if I tap the last or the top cell it should move to the centre of the collection view.

我已尝试设置 contentInsets 和偏移量，但它们似乎不起作用.我想我必须在选择时更改内容大小，并在滚动开始时将其更改回原始大小.

I have tried setting the contentInsets and offsets but they don't seem to work. I think I will have to change the content size on selection and change it back to original when the scrolling begins.

推荐答案

设置 contentInsets 应该在第一个和最后一个单元格周围留出一些额外的空间:

Setting contentInsets should give some extra space around first and last cells:

CGFloat collectionViewHeight = CGRectGetHeight(collectionView.bounds);
[collectionView
  setContentInset:
   UIEdgeInsetsMake(collectionViewHeight/2, 0, collectionViewHeight/2, 0) ];
  // nb, those are top-left-bottom-right

你应该打电话后:

[collectionView scrollToItemAtIndexPath:selectedItemPath
    atScrollPosition:UICollectionViewScrollPositionCenteredVertically
    animated:YES];

传递正确的滚动位置很重要:UICollectionViewScrollPositionCenteredVertically

It's important to pass correct scroll position: UICollectionViewScrollPositionCenteredVertically

这应该正确地居中点击项目.

This should center tapped item properly.

编辑

真的很奇怪，但是设置 UIEdgeInsets 为集合视图方法 scrollToItemAtIndexPath 后不能正常工作，所以我做了一些修改:

It's really strange, but after setting UIEdgeInsets to collection view method scrollToItemAtIndexPath does not works properly, so i make some modification:

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
    CGFloat collectionViewHeight = CGRectGetHeight(self.collectionView.frame);
    [collectionView setContentInset:UIEdgeInsetsMake(collectionViewHeight / 2, 0, collectionViewHeight / 2, 0)];

    UICollectionViewCell *cell = [collectionView cellForItemAtIndexPath:indexPath];
    CGPoint offset = CGPointMake(0,  cell.center.y - collectionViewHeight / 2);
    [collectionView setContentOffset:offset animated:YES];
}

对我来说很好用.

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