swift - UICollectionViewCells 在重新排列后重置其大小

Question

我有一个带有标签的单元格的 UICollectionView，我希望能够通过拖放对它们重新排序。

单元格的大小是用 estimatedItemSize 设置的，因为我希望它们的大小各不相同，具体取决于单元格中文本的大小。我可以让它看起来很好。但是，一旦我使用 collectionView.moveItemAtIndexPath，单元格似乎会采用默认大小。

在移动后立即重置 collectionView 的流布局也不能解决问题。

在viewDidLoad

    let layout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
    layout.estimatedItemSize = CGSize(width: 100, height: 100)
    collectionView.collectionViewLayout = layout

重新排列文本的 UIPanGestureRecognizer

func handlePan(sender: UIPanGestureRecognizer) {
    let locationPoint = sender.locationInView(collectionView)
    if sender.state == UIGestureRecognizerState.Began {

        if let indexPath = collectionView.indexPathForItemAtPoint(locationPoint)? {

            if let cell = collectionView.cellForItemAtIndexPath(indexPath) {
                UIGraphicsBeginImageContext(cell.bounds.size)
                cell.layer.renderInContext(UIGraphicsGetCurrentContext())
                let cellImage = UIGraphicsGetImageFromCurrentImageContext()
                UIGraphicsEndImageContext()

                movingCellImage = UIImageView(image: cellImage)
                movingCellImage.center = locationPoint
                movingCellImage.transform = CGAffineTransformMakeScale(2, 2)
                collectionView.addSubview(movingCellImage)
                cell.alpha = 0
                movingCellOriginalIndexPath = indexPath

            }

        }

    } else if sender.state == UIGestureRecognizerState.Changed {
        movingCellImage.center = locationPoint

    } else if sender.state == UIGestureRecognizerState.Ended {

        if let indexPath = collectionView.indexPathForItemAtPoint(locationPoint)? {

            let cell = collectionView.cellForItemAtIndexPath(movingCellOriginalIndexPath)
            collectionView.moveItemAtIndexPath(movingCellOriginalIndexPath, toIndexPath: indexPath)
            cell?.alpha = 1

        }

        movingCellImage.removeFromSuperview()
    }
}

Answer 1

重新加载动画似乎可以解决问题。
但是之前的布局会保留片刻...您可能需要创建自定义 UICollectionViewLayout 而不是使用 estimatedSize。

if let indexPath = collectionView.indexPathForItemAtPoint(locationPoint)? {
    let cell = collectionView.cellForItemAtIndexPath(movingCellOriginalIndexPath)
    collectionView.moveItemAtIndexPath(movingCellOriginalIndexPath, toIndexPath: indexPath)
    cell?.alpha = 1

    collectionView.reloadSections(NSIndexSet(index: 0)) // not reloadData
}

[更新]

正如您所指出的，关键是 -collectionView:layout:sizeForItemAtIndexPath:。

• 不要将 estimatedSize 设置为 UICollectionViewFlowLayout
• 在上面的委托(delegate)方法中计算每个单元格的大小

像这样:

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
    let str = data[indexPath.item] // string to show in label

    // calculate size. you can use -boundingRectWithSize: as well
    var txtsize = (str as NSString).sizeWithAttributes([ NSFontAttributeName : UIFont.systemFontOfSize(16)]) // specify label's font
    txtsize.width += 10 // add margin if necessary
    txtsize.height = 100 // calculated text height or any value you want

    return txtsize
}