uicollectionview - 拖动时防止通过其中心移动 UICollectionViewCell

Question

我可以通过使用手势识别器拖动它并简化新的 iOS 9 对重新排序的支持来重新排序 iOS 9 上的 UICollectionViewCells。

public func beginInteractiveMovementForItemAtIndexPath(indexPath: NSIndexPath) -> Bool // returns NO if reordering was prevented from beginning - otherwise YES
public func updateInteractiveMovementTargetPosition(targetPosition: CGPoint)
public func endInteractiveMovement()
public func cancelInteractiveMovement()

我注意到当我开始拖动一个单元格时，它的中心会变成触摸位置，我不喜欢那样。

如果我愿意，我希望能够通过它的角落拖动我的单元格。

你知道怎么做吗？

非常感谢。

Answer 1

(用 Swift 3.1 编写)

对于 targetPosition updateInteractiveMovementTargetPosition 的参数功能，而不是像这样直接使用手势识别器的位置......

var location = recognizer.location(in: collectionView)            
collectionView.updateInteractiveMovementTargetPosition(location)

...我创建了一个函数，该函数以要拖动的单元格为中心(collectionView updateInteractiveMovementTargetPosition 将 使用的位置，然后获取手势识别器触摸的位置 在单元格 ，然后从单元格的中心减去它。

func offsetOfTouchFrom(recognizer: UIGestureRecognizer, inCell cell: UICollectionViewCell) -> CGPoint {

    let locationOfTouchInCell = recognizer.location(in: cell)

    let cellCenterX = cell.frame.width / 2
    let cellCenterY = cell.frame.height / 2

    let cellCenter = CGPoint(x: cellCenterX, y: cellCenterY)

    var offSetPoint = CGPoint.zero

    offSetPoint.y = cellCenter.y - locationOfTouchInCell.y
    offSetPoint.x = cellCenter.x - locationOfTouchInCell.x

    return offSetPoint

}

我有一个简单的 var offsetForCollectionViewCellBeingMoved: CGPoint = .zero在我的 View Controller 中，它将存储该偏移量，因此每次手势识别器的位置更改时都不需要调用上面的函数。

所以我的手势识别器的目标看起来像这样:

func collectionViewLongPressGestureRecognizerWasTriggered(recognizer: UILongPressGestureRecognizer) {

    guard let indexPath = collectionView.indexPathForItem(at: recognizer.location(in: self.collectionView)),
        let cell = collectionView.cellForItem(at: indexPath), indexPath.item != 0 else { return }

    switch recognizer.state {

    case .began:

        collectionView.beginInteractiveMovementForItem(at: indexPath)

        // This is the class variable I mentioned above
        offsetForCollectionViewCellBeingMoved = offsetOfTouchFrom(recognizer: recognizer, inCell: cell)

        // This is the vanilla location of the touch that alone would make the cell's center snap to your touch location
        var location = recognizer.location(in: collectionView)

        /* These two lines add the offset calculated a couple lines up to 
        the normal location to make it so you can drag from any part of the 
        cell and have it stay where your finger is. */

        location.x += offsetForCollectionViewCellBeingMoved.x
        location.y += offsetForCollectionViewCellBeingMoved.y

        collectionView.updateInteractiveMovementTargetPosition(location)

    case .changed:

        var location = recognizer.location(in: collectionView)

        location.x += offsetForCollectionViewCellBeingMoved.x
        location.y += offsetForCollectionViewCellBeingMoved.y

        collectionView.updateInteractiveMovementTargetPosition(location)

    case .ended:
        collectionView.endInteractiveMovement()

    default:
        collectionView.cancelInteractiveMovement()
    }
}