如何以编程方式将CollectionView滚动到底部

Question

我使用此代码滚动集合View：

let section = (self.collectionView?.numberOfSections)! - 1;
let item = (self.collectionView?.numberOfItems(inSection: section))! - 1;
let lastIndexPath = IndexPath(item: item, section: section);
self.collectionView?.scrollToItem(at: lastIndexPath, at: .bottom, animated: true);

但我得到错误：

  

*由于未捕获的异常'NSRangeException'终止应用程序，原因：'* - [__ NSArrayM objectAtIndex：]：索引1超出边界[0 ..   0]'

Answer 1

let lastItemIndex = NSIndexPath(forItem: data.count - 1, inSection: 0)
collectionView?.scrollToItemAtIndexPath(lastItemIndex, atScrollPosition: .Bottom, animated: true)

不要忘记：
  - atScrollPosition：.Bottom
  - 并且您需要检查data.count > 0因为if data.count == 0您将收到与您相同的错误

Answer 2

Swift 4 +

extension UICollectionView {
    func scrollToLast() {
        guard numberOfSections > 0 else {
            return
        }

        let lastSection = numberOfSections - 1

        guard numberOfItems(inSection: lastSection) > 0 else {
            return
        }

        let lastItemIndexPath = IndexPath(item: numberOfItems(inSection: lastSection) - 1,
                                          section: lastSection)
        scrollToItem(at: lastItemIndexPath, at: .bottom, animated: true)
    }
}

Answer 3

您可以使用CollectionView

将contentOffset设置为底部动画

这是一个例子

let contentHeight: CGFloat = myCollectionView.contentSize.height
let heightAfterInserts: CGFloat = myCollectionView.frame.size.height - (myCollectionView.contentInset.top + myCollectionView.contentInset.bottom)
if contentHeight > heightAfterInserts {
    myCollectionView.setContentOffset(CGPoint(x: 0, y: myCollectionView.contentSize.height - myCollectionView.frame.size.height), animated: true) 
}

Answer 4

func scrollToItem(at: IndexPath, at: UICollectionViewScrollPosition, animated: Bool)

可以滚动集合视图内容，直到指定的项目可见。如果项目不可见，则会因为未捕获的异常而导致应用终止，例如：NSRangeException＆＃39;原因：＆＃39; ...

Answer 5

var xItem:Int = 0
var currentIndex:NSIndexPath!
@IBOutlet weak var rateCollection: UICollectionView!

@IBAction func btnNextTapped(_ sender: UIButton)
    {
        xItem = xItem+1
        if xItem != arrayRateModel.count
        {
        currentIndex = NSIndexPath(item: xItem, section: 0)
        rateCollection.scrollToItem(at: currentIndex as IndexPath, at: .centeredHorizontally, animated: true)
        }   
    }

Answer 6

的Objective-C

NSInteger noOfsections = [self numberOfSectionsInCollectionView:self.collectionView] - 1;
NSInteger noOFItems = [self collectionView:self.collectionView numberOfItemsInSection:noOfsections] - 1;
NSIndexPath *lastIndexPath = [NSIndexPath indexPathForItem:noOFItems inSection:noOfsections];
[self.collectionView scrollToItemAtIndexPath:lastIndexPath atScrollPosition:UICollectionViewScrollPositionBottom animated:YES];