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 thi

Answer 1

@Ethan's solution - Update Swift 4

in viewDidLoad :

private var dragDropType = NSPasteboard.PasteboardType(rawValue: "private.table-row")

override func viewDidLoad() {
    super.viewDidLoad()

    myTableView.delegate = self
    myTableView.dataSource = self
    myTableView.registerForDraggedTypes([dragDropType])
}

Later on delegate extension :

extension MyViewController: NSTableViewDelegate, NSTableViewDataSource {

    // numerbOfRow and viewForTableColumn methods

    func tableView(_ tableView: NSTableView, pasteboardWriterForRow row: Int) -> NSPasteboardWriting? {

        let item = NSPasteboardItem()
        item.setString(String(row), forType: self.dragDropType)
        return item
    }

    func tableView(_ tableView: NSTableView, validateDrop info: NSDraggingInfo, proposedRow row: Int, proposedDropOperation dropOperation: NSTableView.DropOperation) -> NSDragOperation {

        if dropOperation == .above {
            return .move
        }
        return []
    }

    func tableView(_ tableView: NSTableView, acceptDrop info: NSDraggingInfo, row: Int, dropOperation: NSTableView.DropOperation) -> Bool {

        var oldIndexes = [Int]()
        info.enumerateDraggingItems(options: [], for: tableView, classes: [NSPasteboardItem.self], searchOptions: [:]) { dragItem, _, _ in
            if let str = (dragItem.item as! NSPasteboardItem).string(forType: self.dragDropType), 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
    }

}

Plus, for those it may concerne:

1. If you want to disable certain cells from being dragable, return nil in pasteboardWriterForRows method

2. If you want to prevent drop a certain locations ( too far for instance ) just use return [] in validateDrop's method

3. Do not call tableView.reloadData() synchronously inside func tableView(_ tableView:, acceptDrop info:, row:, dropOperation:). This will disturb Drag and Drop animation, and can be very confusing. Find a way to wait until animation finishes, and async it's reloading