NSTableView reordering row with drag and drop

DragTableController.swift

//
//  ViewController.swift
//  DragTable
//
//  Created by Anna Kim on 2017. 2. 9..
//  Copyright © 2017년 Anna Kim. All rights reserved.
//

import Cocoa

// MARK: - Array Extension
// 원소의 위치 이동을 위한 Array 타입 확장
extension Array {
    mutating func move(from start: Index, to end: Index) {
        guard (0..<count) ~= start, (0...count) ~= end else { return }
        if start == end { return }
        let targetIndex = start < end ? end - 1 : end
        insert(remove(at: start), at: targetIndex)
    }
    
    mutating func move(with indexes: IndexSet, to toIndex: Index) {
        let movingData = indexes.map{ self[$0] }
        let targetIndex = toIndex - indexes.filter{ $0 < toIndex }.count
        for (i, e) in indexes.enumerated() {
            remove(at: e - i)
        }
        insert(contentsOf: movingData, at: targetIndex)
    }
}

// MARK: - View Controller Implementation
class ViewController: NSViewController {

    var names = ["apple", "banana", "cherry", "orange", "pear", "peach" ]
    
    @IBOutlet weak var sourceTableView: NSTableView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        sourceTableView.register(forDraggedTypes: ["public.data"])
        sourceTableView.allowsMultipleSelection = true
    }
    
}



// MARK: - NSTableViewDataSource, NSTableViewDelegate
extension ViewController: NSTableViewDelegate, NSTableViewDataSource {
    
    func numberOfRows(in tableView: NSTableView) -> Int {
        return names.count
    }
    
    
    func tableView(_ tableView: NSTableView, objectValueFor tableColumn: NSTableColumn?, row: Int) -> Any? {
        return names[row]
    }
    
    
    
    // MARK: Allow Drag Operation
    
    /*  tableView(_:writeRowsWith:to:) 를 구현하면서 true를 리턴하게 하면 해당 테이블 뷰에서 드래그가 가능해진다.
     이때, 실제 데이터보다는 선택된 셀들의 인덱스들을 인코딩해버리는 것이 편하다.
     */
    
    func tableView(_ tableView: NSTableView, writeRowsWith rowIndexes: IndexSet, to pboard: NSPasteboard) -> Bool {
        let data = NSKeyedArchiver.archivedData(withRootObject: rowIndexes)
        let item = NSPasteboardItem()
        item.setData(data, forType: "public.data")
        pboard.writeObjects([item])
        return true
    }
    
    
    // MARK: Drag Destination Actions
    func tableView(_ tableView: NSTableView, validateDrop info: NSDraggingInfo, proposedRow row: Int, proposedDropOperation dropOperation: NSTableViewDropOperation) -> NSDragOperation {
        
        guard let source = info.draggingSource() as? NSTableView,
            source === sourceTableView
            else { return [] }
        
        if dropOperation == .above {
            return .move
        }
        return []
    }
    
    
    func tableView(_ tableView: NSTableView, acceptDrop info: NSDraggingInfo, row: Int, dropOperation: NSTableViewDropOperation) -> Bool {
        let pb = info.draggingPasteboard()
        if let itemData = pb.pasteboardItems?.first?.data(forType: "public.data"),
            let indexes = NSKeyedUnarchiver.unarchiveObject(with: itemData) as? IndexSet
        {
            names.move(with: indexes, to: row)
            let targetIndex = row - (indexes.filter{ $0 < row }.count)
            // 드래그했던 셀들을 다시 선택 상태로 만들어 둔다.
            tableView.selectRowIndexes(IndexSet(targetIndex..<targetIndex+indexes.count), byExtendingSelection: false)
            return true
        }
        return false
    }
}