ios - UITableView 使用 NSFetchedResultsController 和 CoreData 意外反弹到 beginUpdates()/endUpdates()/performBatchUpdates()

Question

UITableView 意外反弹 beginUpdates()/endUpdates()/performBatchUpdates() 使用 NSFetchedResultsController 和 CoreData 当行数填满 View 时。重现它非常简单。- 从主从应用程序模板(使用 CoreData)创建一个新项目。- 在 Storyboard 中，删除“showDetail”转场。 (我们不需要详细 View )- 在 MasterViewController 中，将 segue func prepare() 替换为:

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {  
    let event = fetchedResultsController.object(at: indexPath)  
    let timestamp = event.timestamp  
    event.timestamp = timestamp // The idea is to simply update the Event entity.  
  }

启动应用程序(在 iOS 设备或模拟器中)，并添加足够的行来填充 View (在 iPhone SE 中，它有 11 行)。向下 ScrollView ，然后选择任意行。 View 将快速上下弹跳。这是错误还是代码有问题？

Answer 1

好的，我可能找到了解决方案，请告诉我你们的想法。这个想法是在 performBatchUpdates 中处理 insert/delete/move 并将 update 排除在外。所以我创建了这个枚举和属性:

enum FetchedResultsChange<Object> {
  case insert(IndexPath)
  case delete(IndexPath)
  case move(IndexPath, IndexPath, Object)
}
var fetchedResultsChanges: [FetchedResultsChange<Event>] = []

controllerWillChangeContent 变为空:

func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {}

didChange 变成:

func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
    switch type {
    case .insert:
      self.fetchedResultsChanges.append(.insert(newIndexPath!))
    case .delete:
      self.fetchedResultsChanges.append(.delete(indexPath!))
    case .update:
      configureCell(tableView.cellForRow(at: indexPath!)!, withEvent: anObject as! Event) // So this stays untouched.
    case .move:
      self.fetchedResultsChanges.append(.move(indexPath!, newIndexPath!, anObject as! Event))
    }
  }

controllerDidChangeContent 变成:

  func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
    guard self.fetchedResultsChanges.count > 0 else { return }

    tableView.performBatchUpdates({
      repeat {
        let change = self.fetchedResultsChanges.removeFirst()
        switch change {
        case .insert(let newIndexPath):
          tableView.insertRows(at: [newIndexPath], with: .fade)
        case .delete(let indexPath):
          tableView.deleteRows(at: [indexPath], with: .fade)
        case .move(let indexPath, let newIndexPath, let event):
          configureCell(tableView.cellForRow(at: indexPath)!, withEvent: event)
          tableView.moveRow(at: indexPath, to: newIndexPath)
        }
      } while self.fetchedResultsChanges.count > 0
    }, completion: nil)
  }

那你怎么看？