解决方案

Question

我有一个UICollectionView来显示聊天消息。在开始时，我将现有消息加载到collectionView，并使用此方法将collectionView向下滚动到最后一条消息：

- (void)scrollToLastMessageAnimated:(BOOL)animated;
{
    if (_messages.count == 0) { return; }

    NSUInteger indexOfLastSection = _messagesBySections.count - 1;
    NSInteger indexOfMessageInLastSection = [_messagesBySections[indexOfLastSection] count] - 1;
    NSIndexPath *path = [NSIndexPath indexPathForItem:indexOfMessageInLastSection
                                            inSection:indexOfLastSection];

    [_collectionView scrollToItemAtIndexPath:path
                           atScrollPosition:UICollectionViewScrollPositionCenteredVertically
                                   animated:animated];
}

当我在viewDidAppear：方法中调用它而不是在viewWillAppear：方法中调用它时，它才有效。如何在没有动画的情况下向下滚动？

Answer 1

这是......

NSInteger section = [self.collectionView numberOfSections] - 1;
NSInteger item = [self.collectionView numberOfItemsInSection:section] - 1;
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:item inSection:section];
[self.collectionView scrollToItemAtIndexPath:indexPath atScrollPosition:(UICollectionViewScrollPositionBottom) animated:YES];

Answer 2

我还在你的另一个问题中提供了我的答案，但我也在这里写，因为这个答案只与这个问题有关

解决方案

要在视图出现之前滚动最后一个索引处的视图而不崩溃，首先需要触发collectionView数据的重新加载。重新加载后，请调用您的方法滚动视图。

-(void)viewWillAppear:(BOOL)animated {
    [collectionView reloadData];
    [self scrollToLastMessageAnimated:YES];
}

更新

[collectionView setContentOffset:CGPointMake(0, CGFLOAT_MAX)]

Answer 3

Swift 3.0代码：

let index = IndexPath(item: (self.mFetchedResultsControllerVar?.fetchedObjects?.count)! - 1, section: 0)
self.collectionView?.scrollToItem(at: index, at: UICollectionViewScrollPosition.bottom, animated: true)

Answer 4

处理多个/ 0个部分/项目的更简单的解决方案

[(id , in, available_service_type_ids and available_service_type_ids[0] and available_service_type_ids[0][2] or False)]

Answer 5

此扩展程序滚动到实际包含项目的最后一部分。迄今为止的最佳方法。

public extension UICollectionView {
    func scrollToLastItem() {
        scrollToLastItem(animated: true, atScrollPosition: .bottom)
    }

    func scrollToLastItem(animated: Bool, atScrollPosition scrollPosition: UICollectionViewScrollPosition) {
        guard numberOfSections > 0 else {
            return
        }

        var sectionWithItems: SectionInfo?
        for section in Array(0...(numberOfSections - 1)) {
            let itemCount = numberOfItems(inSection: section)
            if itemCount > 0 {
                sectionWithItems = SectionInfo(numberOfItems: itemCount, sectionIndex: section)
            }
        }

        guard let lastSectionWithItems = sectionWithItems else {
            return
        }

        let lastItemIndexPath = IndexPath(row: lastSectionWithItems.numberOfItems - 1, section: lastSectionWithItems.sectionIndex)
        scrollToItem(at: lastItemIndexPath, at: scrollPosition, animated: animated)
    }
}

Answer 6

问题实际上是由有问题的Autolayout限制引起的，看到我的另一个主题是最终帮助我的解决方案：https://stackoverflow.com/a/24033650/2302437

UICollectionView滚动到没有动画的最后一项

6 个答案:

解决方案

更新