NSDiffableDataSourceSnapshot, 그리고 Cocoa
macOS 11.0 이후로 Cocoa에 NSTableViewDiffableDataSource, NSCollectionViewDiffableDataSource, 그리고 NSDiffableDataSourceSnapshot가 추가되었습니다. 마찬가지로 UIKit에도 UITableViewDiffableDataSource와 UICollectionViewDiffableDataSource도 추가되었죠.
raywenderlich에서 이 사용법과 UICollectionLayoutListConfiguration까지 한꺼번에 학습할 수 있는 매우 좋은 자료가 있습니다. iOS 14 Tutorial: UICollectionView List (www.raywenderlich.com/)
하지만 위 가이드는 iOS용입니다. 근데 macOS의 Cocoa도 대충 비슷하게 작동하지 않겠어??? 라는 생각으로 한 번 아래와 같이 짜봅시다.
import Cocoa
class ViewController: NSViewController {
@IBOutlet weak var tableView: NSTableView!
var viewModel: ViewModel = .init()
override func viewDidLoad() {
super.viewDidLoad()
configureDataSource()
}
func configureDataSource() {
viewModel.dataSource = makeDataSource()
viewModel.updateData()
}
func makeDataSource() -> ViewModel.DataSource {
return .init(tableView: tableView) { (tableView, column, row, item) -> NSView in
let cell: NSTableCellView = tableView.makeView(withIdentifier: column.identifier, owner: self)! as! NSTableCellView
cell.textField?.stringValue = item
return cell
}
}
}
class ViewModel {
typealias DataSource = NSTableViewDiffableDataSource<Int, String>
typealias Snapshot = NSDiffableDataSourceSnapshot<Int, String>
var dataSource: DataSource!
func updateData() {
var snapshot: Snapshot = dataSource.snapshot()
snapshot.deleteAllItems()
let section: Int = 0
snapshot.appendSections([section])
snapshot.appendItems(["Apple", "Banana", "Grape"], toSection: section)
dataSource.apply(snapshot, animatingDifferences: true)
}
}
실행해보면… 아래와 같이 런타임 에러가 발생하네요.
2021-04-03 00:02:52.891409+0900 DataSource[4935:102348] *** Assertion failure in -[NSTableViewDiffableDataSourceImpl _applyDifferencesFromSnapshot:completion:], _NSDiffableDataSourceImpl.m:919
2021-04-03 00:02:52.892007+0900 DataSource[4935:102348] Failed to set (contentViewController) user defined inspected property on (NSWindow): Invalid parameter not satisfying: snapshot
음… 검색해도 안 나오네요. 한 번 똑같은 로직을 iOS에도 적용해 볼게요.
import UIKit
class ViewController: UIViewController {
@IBOutlet weak var tableView: UITableView!
var viewModel: ViewModel = .init()
override func viewDidLoad() {
super.viewDidLoad()
configureDataSource()
}
func configureDataSource() {
viewModel.dataSource = makeDataSource()
viewModel.updateData()
}
func makeDataSource() -> ViewModel.DataSource {
return .init(tableView: tableView) { (tableView, indexPath, item) -> UITableViewCell? in
let cell: UITableViewCell = .init()
cell.textLabel?.text = item
return cell
}
}
}
class ViewModel {
typealias DataSource = UITableViewDiffableDataSource<Int, String>
typealias Snapshot = NSDiffableDataSourceSnapshot<Int, String>
var dataSource: DataSource!
func updateData() {
var snapshot: Snapshot = dataSource.snapshot()
snapshot.deleteAllItems()
let section: Int = 0
snapshot.appendSections([section])
snapshot.appendItems(["Apple", "Banana", "Grape"], toSection: section)
dataSource.apply(snapshot, animatingDifferences: true)
}
}
잘 나오네요. -_-; 로직에는 문제가 없다는 소리인데요. 여기서 한 번 고민을 해봅시다. 일단 lldb에서 NSTableViewDiffableDataSourceImpl가 뭐하는 놈인지 부터 알아봅시다.
(lldb) image lookup -rn NSTableViewDiffableDataSourceImpl
14 matches found in /System/Library/Frameworks/AppKit.framework/Versions/C/AppKit:
Address: AppKit[0x00000001832b34c0] (AppKit.__TEXT.__text + 7499876)
Summary: AppKit`-[NSTableViewDiffableDataSourceImpl initWithTableView:] Address: AppKit[0x00000001832b356c] (AppKit.__TEXT.__text + 7500048)
Summary: AppKit`-[NSTableViewDiffableDataSourceImpl dealloc] Address: AppKit[0x00000001832b35d0] (AppKit.__TEXT.__text + 7500148)
Summary: AppKit`-[NSTableViewDiffableDataSourceImpl hasSectionHeaderProvider] Address: AppKit[0x00000001832b35e8] (AppKit.__TEXT.__text + 7500172)
Summary: AppKit`-[NSTableViewDiffableDataSourceImpl setAppliedSnapshot:] Address: AppKit[0x00000001832b3630] (AppKit.__TEXT.__text + 7500244)
Summary: AppKit`-[NSTableViewDiffableDataSourceImpl tableViewSnapshot] Address: AppKit[0x00000001832b3640] (AppKit.__TEXT.__text + 7500260)
Summary: AppKit`-[NSTableViewDiffableDataSourceImpl setTableViewSnapshot:] Address: AppKit[0x00000001832b3688] (AppKit.__TEXT.__text + 7500332)
Summary: AppKit`-[NSTableViewDiffableDataSourceImpl numberOfItemsInSnapshot] Address: AppKit[0x00000001832b36a0] (AppKit.__TEXT.__text + 7500356)
Summary: AppKit`-[NSTableViewDiffableDataSourceImpl applyDifferencesFromSnapshot:animatingDifferences:completion:] Address: AppKit[0x00000001832b3758] (AppKit.__TEXT.__text + 7500540)
Summary: AppKit`-[NSTableViewDiffableDataSourceImpl dataSource] Address: AppKit[0x00000001832b3768] (AppKit.__TEXT.__text + 7500556)
Summary: AppKit`-[NSTableViewDiffableDataSourceImpl setDataSource:] Address: AppKit[0x00000001832b3778] (AppKit.__TEXT.__text + 7500572)
Summary: AppKit`-[NSTableViewDiffableDataSourceImpl(NSTableViewConversions) itemIdentifierForRow:] Address: AppKit[0x00000001832b388c] (AppKit.__TEXT.__text + 7500848)
Summary: AppKit`-[NSTableViewDiffableDataSourceImpl(NSTableViewConversions) rowForItemIdentifier:] Address: AppKit[0x00000001832b397c] (AppKit.__TEXT.__text + 7501088)
Summary: AppKit`-[NSTableViewDiffableDataSourceImpl(NSTableViewConversions) sectionIdentifierForRow:] Address: AppKit[0x00000001832b3a90] (AppKit.__TEXT.__text + 7501364)
Summary: AppKit`-[NSTableViewDiffableDataSourceImpl(NSTableViewConversions) rowForSectionIdentifier:]
보니까 -[NSTableViewDiffableDataSourceImpl applyDifferencesFromSnapshot:animatingDifferences:completion:]에서 문제가 생긴 것 같은데요. 여기서 Symbolic Breakpoint를 걸어주고 register를 읽어오면 (arm64 assembly)
(lldb) register read
General Purpose Registers:
x0 = 0x000060000365f000
x1 = 0x00000001dab3ae0d
x2 = 0x0000000000000000
x3 = 0x0000000000000001
x4 = 0x0000000000000000
x5 = 0x00000001a8f79fc8 libswiftAppKit.dylib`AppKit.NSTableViewDiffableDataSource.apply(_: AppKit.NSDiffableDataSourceSnapshot<A, B>, animatingDifferences: Swift.Bool, completion: Swift.Optional<() -> ()>) -> ()
x6 = 0x00000001ed8577f0 libswiftCore.dylib`protocol witness table for Swift.String : Swift.Hashable in Swift
x7 = 0x888a0001ed8456b8
x8 = 0x00000001dab3a000
x9 = 0xac26fe4110f7002e
x10 = 0x0000600000d1d6c0
x11 = 0x0000000037b33f3d
x12 = 0x0000000000000000
x13 = 0x0000000000000000
x14 = 0x0000000000000000
x15 = 0xffffffffffffffff
x16 = 0x00000001ed009132 (void *)0x8ee800000001ed00
x17 = 0x000000018553f6a0 AppKit`-[NSTableViewDiffableDataSourceImpl applyDifferencesFromSnapshot:animatingDifferences:completion:]
x18 = 0x0000000000000000
x19 = 0x0000000000000001
x20 = 0x000060000365f000
x21 = 0x0000000000000000
x22 = 0x0000000000000000
x23 = 0x00000001daa47335
x24 = 0x0000600002a794d0
x25 = 0x0000000000000000
x26 = 0x000060000365f000
x27 = 0x0000000100000004
x28 = 0x0000000000000001
fp = 0x000000016ddaa180
lr = 0x00000001a8f7a0dc libswiftAppKit.dylib`AppKit.NSTableViewDiffableDataSource.apply(_: AppKit.NSDiffableDataSourceSnapshot<A, B>, animatingDifferences: Swift.Bool, completion: Swift.Optional<() -> ()>) -> () + 276
sp = 0x000000016ddaa100
pc = 0x000000018553f6a0 AppKit`-[NSTableViewDiffableDataSourceImpl applyDifferencesFromSnapshot:animatingDifferences:completion:]
cpsr = 0x60000000
문제가 됐던 arg가 applyDifferencesFromSnapshot인데요, 그럼 register 값은 x2 일텐데 이걸 한 번 보면
(lldb) po $x2
<nil>
저기에 nil을 집어넣는 내부적인 버그가 있네요. -_- 자, 이걸 어떻게 해결해야 하냐
- NSTableViewDiffableDataSource는 NSObject가 아닌 Swift Object이며, Swift 전용입니다. 다시 말해 Swift Object -> NSObject로 Bridging되는 로직이 내부적으로 존재합니다.
- 검색해보니 Objective-C로 작동하는 NSTableViewDiffableDataSourceReference도 존재하네요. 즉,
NSTableViewDiffableDataSource와NSTableViewDiffableDataSourceReference의 Bridging 방식은 다르다는 것을 추측할 수 있으며,NSTableViewDiffableDataSource의 Bridging에서 버그가 있을 것이란 가설을 세웠습니다.
그럼 한 번 NSTableViewDiffableDataSource 대신에 NSTableViewDiffableDataSourceReference로 바꾸면 문제가 해결될지 볼까요? 그 전에 일단 알고 가야 할 점이 있습니다.
NSTableViewDiffableDataSource는SectionIdentifierType,ItemIdentifierType에Hashable,Equatable를 conform하는 모든 Type이 들어갈 수 있습니다.- 하지만
NSTableViewDiffableDataSourceReference는 NSObject만 가능합니다. Item 비교를 위해isEqual(_:)와hash를 override해야 합니다.
자 그럼 한 번 바꿔봅시다. <Int, String>에서 <NSNumber, NSString>으로 바뀐 걸 볼 수 있습니다.
import Cocoa
class ViewController: NSViewController {
@IBOutlet weak var tableView: NSTableView!
var viewModel: ViewModel = .init()
override func viewDidLoad() {
super.viewDidLoad()
configureDataSource()
}
func configureDataSource() {
viewModel.dataSource = makeDataSource()
viewModel.updateData()
}
func makeDataSource() -> ViewModel.DataSource {
return .init(tableView: tableView) { (tableView, column, row, item) -> NSView in
let cell: NSTableCellView = tableView.makeView(withIdentifier: column.identifier, owner: self)! as! NSTableCellView
cell.textField?.stringValue = item as! String
return cell
}
}
}
class ViewModel {
typealias DataSource = NSTableViewDiffableDataSourceReference<NSNumber, NSString>
typealias Snapshot = NSDiffableDataSourceSnapshotReference
var dataSource: DataSource!
func updateData() {
let snapshot: Snapshot = dataSource.snapshot()
snapshot.deleteAllItems()
let section: Int = 0
snapshot.appendSections(withIdentifiers: [section])
snapshot.appendItems(withIdentifiers: ["Apple", "Banana", "Grape"], intoSectionWithIdentifier: section)
dataSource.applySnapshot(snapshot, animatingDifferences: true)
}
}
잘 되네요.😕
다만 animatingDifferences도 NSTableViewDiffableDataSourceReference에 버그가 있으므로, 잘 살펴보시는 걸 추천합니다.