macos - Drag & Drop Reorder Rows on NSTableView

Question

I was just wondering if there was an easy way to set an NSTableView to allow it to reorder its rows without writing any pasteboard code. I only need it to be able to do this internally, within one table. I have no issue writing the pboard code, except that I'm fairly sure that I saw Interface Builder have a toggle for this somewhere / saw it working by default. It certainly seems like a common enough task.

Thanks

Answer 1

Set your table view's datasource to be a class that conforms to NSTableViewDataSource.

Put this in an appropriate place (-applicationWillFinishLaunching, -awakeFromNib, -viewDidLoad or something similar):

tableView.registerForDraggedTypes(["public.data"])

Then implement these three NSTableViewDataSource methods:

tableView:pasteboardWriterForRow:
tableView:validateDrop:proposedRow:proposedDropOperation:
tableView:acceptDrop:row:dropOperation:

Here is fully-working code that supports drag-and-drop reordering multiple rows:

func tableView(tableView: NSTableView, pasteboardWriterForRow row: Int) -> NSPasteboardWriting? {
  let item = NSPasteboardItem()
  item.setString(String(row), forType: "public.data")
  return item
}

func tableView(tableView: NSTableView, validateDrop info: NSDraggingInfo, proposedRow row: Int, proposedDropOperation dropOperation: NSTableViewDropOperation) -> NSDragOperation {
  if dropOperation == .Above {
    return .Move
  }
  return .None
}

func tableView(tableView: NSTableView, acceptDrop info: NSDraggingInfo, row: Int, dropOperation: NSTableViewDropOperation) -> Bool {
  var oldIndexes = [Int]()
  info.enumerateDraggingItemsWithOptions([], forView: tableView, classes: [NSPasteboardItem.self], searchOptions: [:]) {
    if let str = ($0.0.item as! NSPasteboardItem).stringForType("public.data"), index = Int(str) {
            oldIndexes.append(index)
    }
  }

  var oldIndexOffset = 0
  var newIndexOffset = 0

  // For simplicity, the code below uses `tableView.moveRowAtIndex` to move rows around directly.
  // You may want to move rows in your content array and then call `tableView.reloadData()` instead.
  tableView.beginUpdates()
  for oldIndex in oldIndexes {
    if oldIndex < row {
      tableView.moveRowAtIndex(oldIndex + oldIndexOffset, toIndex: row - 1)
      --oldIndexOffset
    } else {
      tableView.moveRowAtIndex(oldIndex, toIndex: row + newIndexOffset)
      ++newIndexOffset
    }
  }
  tableView.endUpdates()

  return true
}

Swift 3 version:

func tableView(_ tableView: NSTableView, pasteboardWriterForRow row: Int) -> NSPasteboardWriting? {
    let item = NSPasteboardItem()
    item.setString(String(row), forType: "private.table-row")
    return item
}

func tableView(_ tableView: NSTableView, validateDrop info: NSDraggingInfo, proposedRow row: Int, proposedDropOperation dropOperation: NSTableViewDropOperation) -> NSDragOperation {
    if dropOperation == .above {
        return .move
    }
    return []
}

func tableView(_ tableView: NSTableView, acceptDrop info: NSDraggingInfo, row: Int, dropOperation: NSTableViewDropOperation) -> Bool {
    var oldIndexes = [Int]()
    info.enumerateDraggingItems(options: [], for: tableView, classes: [NSPasteboardItem.self], searchOptions: [:]) {
        if let str = ($0.0.item as! NSPasteboardItem).string(forType: "private.table-row"), let index = Int(str) {
            oldIndexes.append(index)
        }
    }

    var oldIndexOffset = 0
    var newIndexOffset = 0

    // For simplicity, the code below uses `tableView.moveRowAtIndex` to move rows around directly.
    // You may want to move rows in your content array and then call `tableView.reloadData()` instead.
    tableView.beginUpdates()
    for oldIndex in oldIndexes {
        if oldIndex < row {
            tableView.moveRow(at: oldIndex + oldIndexOffset, to: row - 1)
            oldIndexOffset -= 1
        } else {
            tableView.moveRow(at: oldIndex, to: row + newIndexOffset)
            newIndexOffset += 1
        }
    }
    tableView.endUpdates()

    return true
}