问题
I know it's possible to reorder a single item/cell at a time when using the new UITableViewDropDelegate and UITableViewDragDelegate delegates but is it possible to support handling multiple.
For example in this screenshot I am holding a single item:
And dropping the cell puts it in to place.
However when I grab multiple cells I get the no entry sign and the cells wont reorder:
If I multiple items from another app it works fine, for example dragging multiple messages out of iMessage:
Is it possible to do this when reordering a table view with only local items so that you can reorder quicker?
Here is my code:
UITableViewDragDelegate
extension DotViewController: UITableViewDragDelegate {
func tableView(_ tableView: UITableView, itemsForBeginning session: UIDragSession, at indexPath: IndexPath) -> [UIDragItem] {
return [getDragItem(forIndexPath: indexPath)]
}
func tableView(_ tableView: UITableView, itemsForAddingTo session: UIDragSession, at indexPath: IndexPath, point: CGPoint) -> [UIDragItem] {
return [getDragItem(forIndexPath: indexPath)]
}
func getDragItem(forIndexPath indexPath: IndexPath) -> UIDragItem {
// gets the item
}
}
UITableViewDropDelegate
extension DotViewController: UITableViewDropDelegate {
func tableView(_ tableView: UITableView, canHandle session: UIDropSession) -> Bool {
return true
}
func tableView(_ tableView: UITableView, dropSessionDidUpdate session: UIDropSession, withDestinationIndexPath destinationIndexPath: IndexPath?) -> UITableViewDropProposal {
return UITableViewDropProposal(operation: .move, intent: .insertAtDestinationIndexPath)
}
func tableView(_ tableView: UITableView, performDropWith coordinator: UITableViewDropCoordinator) {
// Handles Drop
}
}
viewDidLoad
override func viewDidLoad() {
super.viewDidLoad()
tableView.dataSource = self
tableView.delegate = self
tableView.dragDelegate = self
tableView.dropDelegate = self
tableView.dragInteractionEnabled = true
}
回答1:
It's possible to do multi-row reordering yourself by providing references to all the selected cells via your drag delegate (e.g. an array of section.row's ) then implementing tableView:performDropWith:withCoordinator to reorder them. (I suspect you know this)
If you want to support reordering by returning a drop proposal of UITableViewDropProposal(operation: .move, intent: .insertAtDestinationIndexPath) so UIKit uses the pre-iOS 11 tableView:moveRowAt:to function then this only supports a single row.
Table view moveRowAt IndexPath to IndexPath. You can continue to implement this, if you like, to support reordering, using Drag and Drop. Because table view is actually going to call this instead of calling through perform drop with coordinator, if you've returned that magic drop proposal and a single row is actually being reordered.
Source: https://developer.apple.com/videos/play/wwdc2017/223/?time=1836
回答2:
I'm afraid I cannot go into much detail here, but here's basically how I was able to get it to work:
- I extended an algorithm I found on StackOverflow to get a working function that I could use to reorder my datasource. Here's my possibly super-inefficient/inaccurate code for this:
Multiple element reordering in array (example is for ints but can be modified to use indexpaths and datasource type:
// Multiple element reordering in array
func reorderList(list: Array<Int>, draggedIndices: Array<Int>, targetIndex: Int) -> Array<Int> {
// Defining the offsets that occur in destination and source indexes when we iterate over them one by one
var array = list
var draggedItemOffset = 0
var targetIndexOffset = 0
// Items being dragged ordered by their indexPaths
let orderedDragIndices = draggedIndices.sorted() // Add {$0.row < $1.row for sorting IndexPaths}
// Items being dragged ordered by their selection order
var selectionOrderDragItems = [Int]()
draggedIndices.forEach { (index) in
selectionOrderDragItems.append(array[index])
}
// Reordering the list
for i in (0...(orderedDragIndices.count - 1)).reversed() {
let removedItem = array.remove(at: orderedDragIndices[i] + draggedItemOffset)
array.insert(removedItem, at: targetIndex + targetIndexOffset)
if (i - 1 >= 0) && orderedDragIndices[i - 1] >= targetIndex {
draggedItemOffset += 1
} else {
draggedItemOffset = 0
targetIndexOffset -= 1
}
}
// Right now the dropped items are in the order of their source indexPaths. Returning them back to the order of selection
for index in Array(targetIndex + targetIndexOffset + 1...targetIndexOffset).sorted(by: >) {
array.remove(at: index)
}
array.insert(contentsOf: selectionOrderDragItems, at: targetIndex + targetIndexOffset + 1)
return array
}
In the dragDelegate and dropDelegate methods, I used single item reordering (UITableViewDropProposal(operation: .move, intent: .insertAtDestinationIndexPath)) to get the free animation where the other cells make space for a drop. However, as the user tapped on additional rows, I collected these additional indexPaths using didSelectRow while the drag session was active.
Using the above array of selected rows, in the performDrop delegate method, I used the algorithm described in (1) to restructure my datasource and reload the tableview section with animation.
I did some additional animation to show the user that rows are being collected under the finger using panGestureRecognizer and making a snapshot of the cell upon selection.
Note that I did not use canMoveRowAt or canEditRowAt or moveRowAt or other traditional methods in this process. I used the performDrop method from the iOS 11 APIs.
Hope it helps, and do reply if you find that the algorithm has some cases where it fails. Thanks and good luck!
来源：https://stackoverflow.com/questions/45169912/is-it-possible-to-use-ios-11-drag-and-drop-to-reorder-multiple-items-cells-at-a