ios - FRC 更新后 TableViewController 不刷新

Question

在 NSFetchedResultsController (FRC) 中选择一行时，我的应用程序允许通过转到详细信息 View Controller 来更改详细信息。保存更改后，编辑的行将返回并插入到 FRC 中。

.update代码在下面的switch中被触发:

func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
    switch type {
    case .update:
        configureCell(cell: tableView.cellForRow(at: indexPath! as IndexPath)!, indexPath: indexPath! as NSIndexPath)
        tableView.reloadRows(at: [indexPath!], with: .automatic)
    case .insert:
        tableView.insertRows(at: [newIndexPath!], with: .automatic)
    case .delete:
        tableView.deleteRows(at: [indexPath!], with: .automatic)
    case .move:
        tableView.moveRow(at: indexPath! as IndexPath, to: newIndexPath! as IndexPath)
    }
}

configureCell() 方法是:

func configureCell(cell: UITableViewCell, indexPath: NSIndexPath) {
    var handicap: Float

    let cellIdentifier = "PlayerTableViewCell"

    guard let cell = tableView.dequeueReusableCell(withIdentifier: cellIdentifier, for: indexPath as IndexPath) as? PlayerTableViewCell else {
            fatalError("The dequeued cell is not an instance of PlayerTableViewCell")
        }

    // Populate cell from the NSManagedObject instance
    guard let player = fetchedResultsController.object(at: indexPath as IndexPath) as? Golfer else {
        fatalError("Unexpected Object in FetchedResultsController")
    }

    let firstName = player.value(forKey: "firstName") as! String?
    let lastName = player.value(forKey: "lastName") as! String?
    let fullName = firstName! + " " + lastName!
    handicap = player.value(forKey: "exactHandicap") as! Float

    cell.playerFullName?.text = fullName

    cell.playerPhoto.image = UIImage(data: player.value(forKey: "photo") as! Data)

    cell.numExactHandicap.text = "\(Int(handicap))"
    cell.numStrokesReceived.text = "\(handicap.cleanValue)"

    print("Object for configuration: \(player)")
}

细胞类定义是:

class PlayerTableViewCell: UITableViewCell {

    //MARK: Properties
    @IBOutlet weak var playerFullName: UILabel!
    @IBOutlet weak var playerPhoto: UIImageView!
    @IBOutlet weak var exactHandicapLabel: UILabel!
    @IBOutlet weak var strokesReceivedLabel: UILabel!
    @IBOutlet weak var numExactHandicap: UILabel!
    @IBOutlet weak var numStrokesReceived: UILabel!

   override func awakeFromNib() {
        super.awakeFromNib()
        // Initialization code
    }

    override func setSelected(_ selected: Bool, animated: Bool) {
        super.setSelected(selected, animated: animated)

        // Configure the view for the selected state
    }

-- 编辑 #1 --

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    // Table view cells are reused and should be dequeued using a cell identifier
    let cell = tableView.dequeueReusableCell(withIdentifier: "PlayerTableViewCell", for: indexPath)

    configureCell(cell: cell, indexPath: indexPath as NSIndexPath)

    return cell
}

我得到的行为在很多方面都是出乎意料的。

1. 屏幕上的数据不会随着 .update 代码的处理而更新，保留 FRC 中预先编辑的值。

2. 只有当我选择表格中的同一行时，该行才会刷新。 IE。它显示旧值，但在我再次选择该行时更改为新值，然后再次启动已编辑的行。

3. 当我选择除第 0 行以外的任何行时，它第一次将单元格中的所有值设置为 Storyboard中显示的默认值。但是，在任何情况下，第 0 行从不在 segue 之前更改。

非常欢迎任何见解!

-- 编辑#3 [2017 年 4 月 20 日]--

一段时间以来，我一直在努力解决这个问题。核心问题仍然存在 - 屏幕上的数据不会在 .update 代码处理后刷新，保留 FRC 中的预编辑值。

关键代码段现在看起来像这样:

func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
    switch type {
    case .update:
        golferView.reloadRows(at: [indexPath!], with: .automatic)
    case .insert:
        golferView.insertRows(at: [newIndexPath!], with: .automatic)
    case .delete:
        golferView.deleteRows(at: [indexPath!], with: .automatic)
    case .move:
        golferView.moveRow(at: indexPath! as IndexPath, to: newIndexPath! as IndexPath)
    }
}

func configureCell(cell: UITableViewCell, indexPath: NSIndexPath) {
    var handicap: Float
    var player: Golfer

    let cellIdentifier = "PlayerTableViewCell"

    guard let cell = golferView.dequeueReusableCell(withIdentifier: cellIdentifier, for: indexPath as IndexPath) as? PlayerTableViewCell else {
        fatalError("The dequeued cell is not an instance of PlayerTableViewCell")
    }

    // Populate cell from the NSManagedObject instance
    player = fetchedResultsController.object(at: indexPath as IndexPath)

    let firstName = player.value(forKey: "firstName") as! String?
    let lastName = player.value(forKey: "lastName") as! String?
    let fullName = firstName! + " " + lastName!
    handicap = player.value(forKey: "exactHandicap") as! Float

    cell.playerFullName?.text = fullName

    cell.playerPhoto.image = UIImage(data: player.value(forKey: "photo") as! Data)

    cell.numExactHandicap.text = "\(Int(handicap))"
    cell.numStrokesReceived.text = "\(handicap.cleanValue)"

    print("Object for configuration: \(player). And cell values are = \(String(describing: cell.playerFullName?.text)), \(String(describing: cell.numExactHandicap.text)), \(String(describing: cell.numStrokesReceived.text))")
}

我已验证 controller() 方法正确触发并且 .update 开关触发 reloadRows。这反过来会触发 configureCell()，其中从 FRC 返回的行的内容是正确的，并且插入到单元格中的值与从 FRC 返回的匹配。它只是不会刷新 UI。

Answer 1

在调查内存使用问题时，我偶然发现了对 dequeueReusableCell 的重复调用，修复后解决了我一直遇到的问题。

在我的文章中，dequeueReusableCell 在 configureCell 中被调用。在 override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell 调用中调用 configureCell 之前也会调用它。

我现在回到正轨了!