UICollectionView当前可见细胞指数UICollectionView当前可见细胞指数(U

我使用UICollectionView第一次在我的iPad应用。 我已设置UICollectionView使得它的尺寸和泡孔尺寸是相同的，只有一次电池在一次显示装置。

问题：现在，当用户滚动UICollectionView我需要知道哪些细胞是可见我不得不更新变化的其他UI元素。 我没有找到这方面的任何委托方法。 我怎样才能做到这一点？

码：

[self.mainImageCollection setTag:MAIN_IMAGE_COLLECTION_VIEW];
[self.mainImageCollection registerClass:[InspirationMainImageCollectionCell class] forCellWithReuseIdentifier:@"cellIdentifier"];
[self.mainImageFlowLayout setScrollDirection:UICollectionViewScrollDirectionHorizontal];
[self.mainImageFlowLayout setMinimumInteritemSpacing:0.0f];
[self.mainImageFlowLayout setMinimumLineSpacing:0.0f];
self.mainImageFlowLayout.minimumLineSpacing = 0;
[self.mainImageCollection setPagingEnabled:YES];
[self.mainImageCollection setShowsHorizontalScrollIndicator:NO];
[self.mainImageCollection setCollectionViewLayout:self.mainImageFlowLayout];

我曾尝试：

至于UICollectionView符合UIScrollView ，我当用户滚动结尾UIScrollViewDelegate方法

-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView

但上述内部功能如何才能得到当前可见的细胞指数UICollectionView ???

Answer 1:

该方法[的CollectionView visibleCells]给你想要的一切visibleCells阵列。 当你想使用它

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView{
    for (UICollectionViewCell *cell in [self.mainImageCollection visibleCells]) {
        NSIndexPath *indexPath = [self.mainImageCollection indexPathForCell:cell];
        NSLog(@"%@",indexPath);
    }
}

Answer 2:

indexPathsForVisibleItems可能适用于大多数情况，但有时它与一个以上的索引路径返回一个数组，它可能会非常棘手搞清楚你想要的。 在这些情况下，你可以这样做：

CGRect visibleRect = (CGRect){.origin = self.collectionView.contentOffset, .size = self.collectionView.bounds.size};
CGPoint visiblePoint = CGPointMake(CGRectGetMidX(visibleRect), CGRectGetMidY(visibleRect));
NSIndexPath *visibleIndexPath = [self.collectionView indexPathForItemAtPoint:visiblePoint];

这尤其适用于当您的收藏视图中的每个项目占据了整个屏幕。

斯威夫特版本

let visibleRect = CGRect(origin: collectionView.contentOffset, size: collectionView.bounds.size)
let visiblePoint = CGPoint(x: visibleRect.midX, y: visibleRect.midY)
let visibleIndexPath = collectionView.indexPathForItem(at: visiblePoint)

Answer 3:

工作组合在雨燕2.2的答案：

 func scrollViewDidEndDecelerating(scrollView: UIScrollView) {

        var visibleRect = CGRect()

        visibleRect.origin = self.collectionView.contentOffset
        visibleRect.size = self.collectionView.bounds.size

        let visiblePoint = CGPointMake(CGRectGetMidX(visibleRect), CGRectGetMidY(visibleRect))

        let visibleIndexPath: NSIndexPath = self.collectionView.indexPathForItemAtPoint(visiblePoint)

        guard let indexPath = visibleIndexPath else { return } 
        print(indexPath)

    }

迅速3迅速4：

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
    var visibleRect = CGRect()

    visibleRect.origin = collectionView.contentOffset
    visibleRect.size = collectionView.bounds.size

    let visiblePoint = CGPoint(x: visibleRect.midX, y: visibleRect.midY)

    guard let indexPath = collectionView.indexPathForItem(at: visiblePoint) else { return } 

    print(indexPath)
}

Answer 4:

为了完整起见，这是最终为我工作的方法。 这是@Anthony的＆@伊恩的方法的组合。

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
      CGRect visibleRect = (CGRect){.origin = self.collectionView.contentOffset, .size = self.collectionView.bounds.size};
      CGPoint visiblePoint = CGPointMake(CGRectGetMidX(visibleRect), CGRectGetMidY(visibleRect));
      NSIndexPath *visibleIndexPath = [self.collectionView indexPathForItemAtPoint:visiblePoint];
      NSLog(@"%@",visibleIndexPath);
}

Answer 5:

只是要添加为他人：出于某种原因，我没有不获取是当我滚动到的CollectionView 以前的细胞与pagingEnabled用户可见的单元格。

所以，我插入的代码里面dispatch_async给它一些“空气”，这对我的作品。

-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    dispatch_async(dispatch_get_main_queue(), ^{
            UICollectionViewCell * visibleCell= [[self.collectionView visibleCells] objectAtIndex:0];


            [visibleCell doSomthing];
        });
}

Answer 6:

这将可能是最好用UICollectionViewDelegate方法：（SWIFT 3）

// Called before the cell is displayed    
func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
    print(indexPath.row)
}

// Called when the cell is displayed
func collectionView(_ collectionView: UICollectionView, didEndDisplaying cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
    print(indexPath.row)
}

Answer 7:

对于雨燕3.0

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    let visibleRect = CGRect(origin: colView.contentOffset, size: colView.bounds.size)
    let visiblePoint = CGPoint(x: visibleRect.midX, y: visibleRect.midY)
    let indexPath = colView.indexPathForItem(at: visiblePoint)
}

Answer 8:

雨燕3.0

这将给你indexPath可见细胞简单的解决方案..

yourCollectionView.indexPathsForVisibleItems 

将返回indexpath的阵列。

只要采取的第一个对象从数组这样。

yourCollectionView.indexPathsForVisibleItems.first

我想这应该能正常使用的Objective - C为好。

Answer 9:

UICollectionView当前可见细胞指数：斯威夫特3

var visibleCurrentCellIndexPath: IndexPath? {
    for cell in self.collectionView.visibleCells {
        let indexPath = self.collectionView.indexPath(for: cell)
        return indexPath
     }

     return nil
}

Answer 10:

您可以使用scrollViewDidEndDecelerating ：此

//@property (strong, nonatomic) IBOutlet UICollectionView *collectionView;

   - (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView{

        for (UICollectionViewCell *cell in [self.collectionView visibleCells]) {
            NSIndexPath *indexPath = [self.collectionView indexPathForCell:cell];
            NSUInteger lastIndex = [indexPath indexAtPosition:[indexPath length] - 1];
            NSLog(@"visible cell value %d",lastIndex);
        }

    }

Answer 11:

转换@安东尼的回答雨燕3.0完美地工作对我来说：

func scrollViewDidScroll(_ scrollView: UIScrollView) {

    var visibleRect = CGRect()
    visibleRect.origin = yourCollectionView.contentOffset
    visibleRect.size = yourCollectionView.bounds.size
    let visiblePoint = CGPoint(x: CGFloat(visibleRect.midX), y: CGFloat(visibleRect.midY))
    let visibleIndexPath: IndexPath? = yourCollectionView.indexPathForItem(at: visiblePoint)
    print("Visible cell's index is : \(visibleIndexPath?.row)!")
}

Answer 12:

这是老问题，但在我的情况...

- (void) scrollViewWillBeginDragging:(UIScrollView *)scrollView {

    _m_offsetIdx = [m_cv indexPathForCell:m_cv.visibleCells.firstObject].row;
}

- (void) scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    _m_offsetIdx = [m_cv indexPathForCell:m_cv.visibleCells.lastObject].row;
}

Answer 13:

还要检查这个片段

let isCellVisible = collectionView.visibleCells.map { collectionView.indexPath(for: $0) }.contains(inspectingIndexPath)

Answer 14:

试试这个，它的工作原理。 （在下面的例子中我有3个细胞例如）。

    func scrollViewDidEndDecelerating(scrollView: UIScrollView) {
    let visibleRect = CGRect(origin: self.collectionView.contentOffset, size: self.collectionView.bounds.size)
    let visiblePoint = CGPointMake(CGRectGetMidX(visibleRect), CGRectGetMidY(visibleRect))
    let visibleIndexPath = self.collectionView.indexPathForItemAtPoint(visiblePoint)
    if let v = visibleIndexPath {
        switch v.item {
        case 0: setImageDescription()
            break
        case 1: setImageConditions()
            break
        case 2: setImageResults()
            break
        default: break
        }
    }

Answer 15:

迅速3迅速4：

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
   var visibleRect = CGRect()

   visibleRect.origin = collectionView.contentOffset
   visibleRect.size = collectionView.bounds.size

   let visiblePoint = CGPoint(x: visibleRect.midX, y: visibleRect.midY)

   guard let indexPath = collectionView.indexPathForItem(at: visiblePoint) else { return } 

   print(indexPath[1])
}

如果你想显示实际数量比你可以添加+1

文章来源: UICollectionView current visible cell index