Question

我有点困惑，我无法解决一件非常简单的事情。

我的CollectionView有50个单元格，我想使用“下一步”按钮和“后退”按钮在这些单元格之间来回滚动。我知道scrollToItemAtIndexPath方法，但是在找到正确的IndexPath时遇到问题。有人可以帮助我吗？

这是我的代码：

// My personal method

-(void)scrollYearAtIndex:(NSInteger)index {
    NSIndexPath *indexPath = [NSIndexPath indexPathForItem:index inSection:0];
    [_collectionView scrollToItemAtIndexPath:indexPath atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:YES];
}

// Show Next Items
-(void)didScrollNextYear {
    [self scrollYearAtIndex:????];
}

// Show Previous Items
-(void)didScrollPreviousYear {
    [self scrollYearAtIndex:????];
}

Answer 1

let indexPaths : NSArray = self.collectionView!.indexPathsForSelectedItems()
let indexPath : NSIndexPath = indexPaths[0] as NSIndexPath

这将为您提供当前选定的索引路径。在didScrollNextYear方法中，将indexPath.row加1。在didScrollPreviousYear中，将indexPath.row减1。

示例代码：

// Show Next Items
-(void)didScrollNextYear {
    let indexPaths : NSArray = self.collectionView!.indexPathsForSelectedItems()
    let indexPath : NSIndexPath = indexPaths[0] as NSIndexPath

    [self scrollYearAtIndex: indexPath.row+1];
}

Answer 2

我在Swift中给出了答案。您可以在Objective-C中编写相同的逻辑。

要获取下一个indexPath，请获取排序后的last数组的indexPath indexPathsForVisibleItems并加1。

要获取先前的indexPath，请获取排序后的first数组的indexPath indexPathsForVisibleItems并递减1。

func didScrollNextYear() {
    if let index = self.collectionView.indexPathsForVisibleItems.sorted().last?.row {
        let nextIndex = index+1
        if nextIndex < self.collectionView.numberOfItems(inSection: 0) {
            self.collectionView.scrollToItem(at: IndexPath(row: nextIndex, section: 0), at: .centeredHorizontally, animated: true)
        }
    }
}

func didScrollPreviousYear() {
    if let index = self.collectionView.indexPathsForVisibleItems.sorted().first?.row {
        let previousIndex = index-1
        if previousIndex >= 0 {
            self.collectionView.scrollToItem(at: IndexPath(row: previousIndex, section: 0), at: .centeredHorizontally, animated: true)
        }
    }
}

Answer 3

调用此功能可进入下一个和上一个按钮IBAction

 func scrollToNextCell()
{

    let collectionView = yourCollectionView
    let cellSize = CGRect(x: 0, y: 0, width: self.view.frame.width, height: self.view.frame.height)
    let contentOffset = collectionView!.contentOffset;
    collectionView!.scrollRectToVisible(CGRect(x: contentOffset.x + cellSize.width, y: contentOffset.y, width: cellSize.width, height: cellSize.height), animated: true)
}

func scrollToPreviousCell()
{

    let collectionView = yourCollectionView
    let cellSize = CGRect(x: 0, y: 0, width: self.view.frame.width, height: self.view.frame.height)
    let contentOffset = collectionView!.contentOffset;
    collectionView!.scrollRectToVisible(CGRect(x: contentOffset.x - cellSize.width, y: contentOffset.y, width: cellSize.width, height: cellSize.height), animated: true)
}

以编程方式滚动到带有UIButton的项目UICollectionView

3 个答案: