检测最接近collectionview中心的collectionviewcell

问题描述

可疑，我在下面正在做一些根本错误的事情...我有一个水平的collectionview，拖动后我想将最近的单元格捕捉到中心.但是我的结果无法预测...我在这里做错了什么?

Suspect I am doing something fundamentally wrong below... I have a horizontal collectionview and after dragging I want to snap the closest cell to the center. But my results are unpredictable... what am I doing wrong here?

    func scrollViewDidEndDragging(scrollView: UIScrollView, willDecelerate decelerate: Bool) {
    // Find collectionview cell nearest to the center of collectionView
    // Arbitrarily start with the last cell (as a default)
    var closestCell : UICollectionViewCell = collectionView.visibleCells()[0];
    for cell in collectionView!.visibleCells() as [UICollectionViewCell] {
        let closestCellDelta = abs(closestCell.center.x - collectionView.bounds.size.width/2.0)
        let cellDelta = abs(cell.center.x - collectionView.bounds.size.width/2.0)
        if (cellDelta < closestCellDelta){
            closestCell = cell
        }
    }
    let indexPath = collectionView.indexPathForCell(closestCell)
    collectionView.scrollToItemAtIndexPath(indexPath!, atScrollPosition: UICollectionViewScrollPosition.CenteredHorizontally, animated: true)
}

推荐答案

原来，我的原始代码缺少collecitonview内容偏移量.另外，我将居中位置移到了scrollViewDidEndDecelerating回调中.我已经修改了原始代码，并将其包含在下面.

Turns out my original code was missing accounting for the collecitonview content offset. In addition, I've moved the centering into the scrollViewDidEndDecelerating callback. I've modified the original code and included it below.

    func scrollViewDidEndDecelerating(scrollView: UIScrollView) {
    // Find collectionview cell nearest to the center of collectionView
    // Arbitrarily start with the last cell (as a default)
    var closestCell : UICollectionViewCell = collectionView.visibleCells()[0];
    for cell in collectionView!.visibleCells() as [UICollectionViewCell] {
        let closestCellDelta = abs(closestCell.center.x - collectionView.bounds.size.width/2.0 - collectionView.contentOffset.x)
        let cellDelta = abs(cell.center.x - collectionView.bounds.size.width/2.0 - collectionView.contentOffset.x)
        if (cellDelta < closestCellDelta){
            closestCell = cell
        }
    }
    let indexPath = collectionView.indexPathForCell(closestCell)
    collectionView.scrollToItemAtIndexPath(indexPath!, atScrollPosition: UICollectionViewScrollPosition.CenteredHorizontally, animated: true)
}

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