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更改行时发生反弹

nsfetchedresultscontroller core-data uitableview swift ios

J. Doe · 技术社区 · 7 年前

差错

CoreData 用一个 NSFetchResultController 使数据显示在 UITableView . 我有一个问题,那就是 UITableView 更改 contentOffSet.y 插入/移动/删除新行时。当用户滚动到(例如中间)时 UITableView 插入新行时反弹。

此github链接到一个项目,该项目包含复制此行为的最少代码: https://github.com/Jasperav/FetchResultControllerGlitch

这显示出故障。我站在我的身体中间 UITableView 内容偏移量.y .:

类似问题

How to prevent from scrolling UITableView up when NSFetchedResultsController add new record? 因为我明确设置了 rowHeight 和 estimatedRowHeight .
Error: UITableView jump to top with UITableViewAutomaticDimension endUpdates 没有运气
UITableView powered by FetchedResultsController with UITableViewAutomaticDimension - Cells move when table is reloaded 与第一个链接相同,我设置了 行高 和 估计重量 .

关注

我也试着换成 performBatchUpdates begin/endUpdates ,但也没有成功。

这个 UITableView 这些行对用户不可见 . 我想这样的事情应该是现成的。

最终目标

当用户完全滚动到插入新行的顶部(对于WhatsApp,这是底部)时 UITableView 内容偏移量.y .
当用户没有完全滚动到顶部(或底部,取决于插入新行的位置)时,插入新行时,用户看到的单元格不应反弹。这对应用程序的用户体验非常不利。
我在移动/删除单元格时也看到这种行为。有什么简单的方法可以解决所有的问题吗?

如果 UICollectionView 会更合适,这样就可以了。

我正在尝试复制WhatsApp聊天屏幕。我不确定他们是否使用NSFetchResultController,但除此之外,最终的目标是为他们提供准确的用户体验。因此,插入、移动、删除和更新单元格应该像WhatsApp那样进行。因此,对于一个有效的例子:转到WhatsApp,对于一个不起作用的例子:下载项目。

复制粘贴代码

代码(视图控制器.swift):

import CoreData
import UIKit

class ViewController: UIViewController, NSFetchedResultsControllerDelegate, UITableViewDataSource, UITableViewDelegate {
    
    let tableView = MyTableView()
    let resultController = ViewController.createResultController()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Initial cells
        for i in 0...40 {
            let x = SomeEntity(context: CoreDataContext.persistentContainer.viewContext)
            
            x.something = randomString(length: i + 1)
            x.date = Date()
            x.height = Float.random(in: 50...100)
        }
        
        Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { (_) in
            let x = SomeEntity(context: CoreDataContext.persistentContainer.viewContext)
            
            x.something = self.randomString(length: Int.random(in: 10...50))
            x.date = Date()
            x.height = Float.random(in: 50...100)
        }
        
        resultController.delegate = self
        
        view.addSubview(tableView)
        tableView.translatesAutoresizingMaskIntoConstraints = false
        tableView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor).isActive = true
        tableView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor).isActive = true
        tableView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor).isActive = true
        tableView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor).isActive = true
        
        tableView.delegate = self
        tableView.dataSource = self
        tableView.estimatedRowHeight = 75
        
        
        try! resultController.performFetch()
    }
    
    public func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
        switch type {
        case .insert:
            tableView.insertRows(at: [newIndexPath!], with: .automatic)
        case .delete:
            tableView.deleteRows(at: [indexPath!], with: .automatic)
        case .move:
            tableView.deleteRows(at: [indexPath!], with: .automatic)
            tableView.insertRows(at: [newIndexPath!], with: .automatic)
        case .update:
            tableView.moveRow(at: indexPath!, to: newIndexPath!)
        }
    }
    
    func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        tableView.beginUpdates()
    }
    
    public func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        tableView.endUpdates()
    }
    
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return resultController.fetchedObjects?.count ?? 0
    }
    
    func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
        return CGFloat(resultController.object(at: indexPath).height)
    }
    
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath) as! MyTableViewCell
        
        cell.textLabel?.text = resultController.object(at: indexPath).something

        return cell
    }

    
    private static func createResultController() -> NSFetchedResultsController<SomeEntity> {
        let fetchRequest: NSFetchRequest<SomeEntity> = SomeEntity.fetchRequest()
        
        fetchRequest.sortDescriptors = [NSSortDescriptor(key: "date", ascending: false)]
        
        return NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: CoreDataContext.persistentContainer.viewContext, sectionNameKeyPath: nil, cacheName: nil)
    }
    
    func randomString(length: Int) -> String {
        let letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
        return String((0...length-1).map{ _ in letters.randomElement()! })
    }
}

class MyTableView: UITableView {
    init() {
        super.init(frame: .zero, style: .plain)
        
        register(MyTableViewCell.self, forCellReuseIdentifier: "cell")
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

class MyTableViewCell: UITableViewCell {
    
}

class CoreDataContext {
    static let persistentContainer: NSPersistentContainer =  {
        let container = NSPersistentContainer(name: "FetchViewControllerGlitch")
        
        container.loadPersistentStores(completionHandler: { (nsPersistentStoreDescription, error) in
            guard let error = error else {
                return
            }
            fatalError(error.localizedDescription)
        })
        
        return container
    }()
}

6 回复 | 直到 6 年前

Pooja Kamath 7 年前

   let lastScrollOffset = tableView.contentOffset;
   tableView.beginUpdates();
   tableView.insertRows(at: [newIndexPath!], with: .automatic);
   tableView.endUpdates();
   tableView.layer.removeAllAnimations();
   tableView.setContentOffset(lastScrollOffset, animated: false);

尽可能为所有表格单元格类型建立估计高度。即使高度有点动态,这也有助于UITableView。
保存滚动位置,并在更新tableView并调用endUpdates()后重置内容偏移量。

你也可以检查这个 tutorial

taka 7 年前

如果用户向下滚动表视图,则通过删除结果控制器.delegate
如果用户返回到表视图的顶部,则通过设置结果控制器.delegate再一次
禁用时间之间的同步差异

这些更改将在fetch重新启动后应用。

我也试着调整一下 controller(_:didChange:at:for:newIndexPath:) 但根本没用。

代码如下。

import CoreData
import UIKit

class ViewController: UIViewController, NSFetchedResultsControllerDelegate, UITableViewDataSource, UITableViewDelegate, UIScrollViewDelegate {

    let tableView = MyTableView()
    let resultController = ViewController.createResultController()
    var needsSync = false

    override func viewDidLoad() {
        super.viewDidLoad()

        // Initial cells
        for i in 0...40 {
            let x = SomeEntity(context: CoreDataContext.persistentContainer.viewContext)

            x.something = randomString(length: i + 1)
            x.date = Date()
            x.height = Float.random(in: 50...100)
        }

        Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { (_) in
            let x = SomeEntity(context: CoreDataContext.persistentContainer.viewContext)

            x.something = self.randomString(length: Int.random(in: 10...50))
            x.date = Date()
            x.height = Float.random(in: 50...100)
        }

        resultController.delegate = self

        view.addSubview(tableView)
        tableView.translatesAutoresizingMaskIntoConstraints = false
        tableView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor).isActive = true
        tableView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor).isActive = true
        tableView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor).isActive = true
        tableView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor).isActive = true

        tableView.delegate = self
        tableView.dataSource = self
        tableView.estimatedRowHeight = 75


        try! resultController.performFetch()
    }

    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let threshold = CGFloat(100)
        if scrollView.contentOffset.y > threshold && resultController.delegate != nil {
            resultController.delegate = nil
        }
        if scrollView.contentOffset.y <= threshold && resultController.delegate == nil {
            resultController.delegate = self
            needsSync = true
            try! resultController.performFetch()
        }
    }

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

    func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        if needsSync {
            tableView.reloadData()
        }
        tableView.beginUpdates()
    }

    public func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        if needsSync {
            needsSync = false
        }
        tableView.endUpdates()
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return resultController.fetchedObjects?.count ?? 0
    }

    func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
        return CGFloat(resultController.object(at: indexPath).height)
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath) as! MyTableViewCell

        cell.textLabel?.text = resultController.object(at: indexPath).something

        return cell
    }


    private static func createResultController() -> NSFetchedResultsController<SomeEntity> {
        let fetchRequest: NSFetchRequest<SomeEntity> = SomeEntity.fetchRequest()

        fetchRequest.sortDescriptors = [NSSortDescriptor(key: "date", ascending: false)]

        return NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: CoreDataContext.persistentContainer.viewContext, sectionNameKeyPath: nil, cacheName: nil)
    }

    func randomString(length: Int) -> String {
        let letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
        return String((0...length-1).map{ _ in letters.randomElement()! })
    }
}

class MyTableView: UITableView {
    init() {
        super.init(frame: .zero, style: .plain)

        register(MyTableViewCell.self, forCellReuseIdentifier: "cell")
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

class MyTableViewCell: UITableViewCell {

}

class CoreDataContext {
    static let persistentContainer: NSPersistentContainer =  {
        let container = NSPersistentContainer(name: "FetchViewControllerGlitch")

        container.loadPersistentStores(completionHandler: { (nsPersistentStoreDescription, error) in
            guard let error = error else {
                return
            }
            fatalError(error.localizedDescription)
        })

        return container
    }()
}

Nishant Pathania 7 年前

做这个

tableView.bounces = false

它会起作用的

Jon Rose 7 年前

第一步:定义“不动”的含义。对人类来说,很明显它是在跳跃。但是计算机看到contentOffset保持不变。因此,让我们非常精确地定义,第一个有可见顶部的细胞,在改变后应该保持在它原来的位置。所有其他细胞都可以移动,但这是我们的锚。

var somethingIdOfAnchorPoint:String?
var offsetAnchorPoint:CGFloat?

func findHighestCellThatStartsInFrame() -> UITableViewCell? {
  var anchorCell:UITableViewCell?
  for cell in self.tableView.visibleCells {
    let topIsInFrame = cell.frame.origin.y >= self.tableView.contentOffset.y
    if topIsInFrame {

      if let currentlySelected = anchorCell{
        let isHigerUpInView = cell.frame.origin.y < currentlySelected.frame.origin.y
        if  isHigerUpInView {
          anchorCell = cell
        }
      }else{
        anchorCell = cell

      }
    }
  }
  return anchorCell
}

func setAnchorPoint() {
  self.somethingIdOfAnchorPoint = nil;
  self.offsetAnchorPoint = nil;

  if let cell = self.findHighestCellThatStartsInFrame() {
    self.offsetAnchorPoint = cell.frame.origin.y - self.tableView.contentOffset.y
    if let indexPath = self.tableView.indexPath(for: cell) {
      self.somethingIdOfAnchorPoint = resultController.object(at: indexPath).something
    }
  }
}

当我们打电话的时候 setAnchorPoint 我们找到并记住哪个实体(不是 indexPath

下一个让我们打电话 刚毛点

 func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
      self.setAnchorPoint()
      tableView.beginUpdates()
  }

public func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
    tableView.endUpdates()
    self.tableView.layoutSubviews()
    self.scrollToAnchorPoint()
}

func scrollToAnchorPoint() {
  if let somethingId = somethingIdOfAnchorPoint, let offset = offsetAnchorPoint {
    if let item = resultController.fetchedObjects?.first(where: { $0.something == somethingId }),
      let indexPath = resultController.indexPath(forObject: item) {
        let rect = self.tableView.rectForRow(at: indexPath)
        let contentOffset = rect.origin.y - offset
        self.tableView.setContentOffset(CGPoint.init(x: 0, y: contentOffset), animated: false)
    }
  }
}

就这样!当视图完全滚动到顶部时,这不会像您所做的那样,但我相信您自己可以处理这种情况。

Shivam Gaur 7 年前

你可以试试这个,这是一个编辑上面普亚的答案,我已经面临的问题一样,你的 UIView.PerformWithout动画

 UIView.performWithoutAnimation {

        let lastScrollOffset = tableView.contentOffset;
        tableView.beginUpdates();
        tableView.insertRows(at: [newIndexPath!], with: .automatic);
        tableView.endUpdates();
        tableView.setContentOffset(lastScrollOffset, animated: false); 
    }

编辑

您也可以尝试上面的方法,但不必插入行,您可以在tableview上使用reload data,但在此之前,请将提取的数据附加到数据源,并在块内设置最后一个contentOffset。

Ralf 7 年前

表视图是一个复杂的野兽。它的行为因其配置而异。表视图在插入、更新、删除和移动行时调整内容偏移量。如果在表视图控制器中使用表视图,则调用scrollview委托方法scrollViewDidScroll(216;:)。

为了解决这个问题,我重建了你的代码。您的ViewController不再基于UIViewController,而是基于UITableViewController。解决方案的关键部分是fixUpdateContentOffset属性的处理和使用。

import CoreData
import UIKit

class ViewController: UITableViewController, NSFetchedResultsControllerDelegate {

    let resultController = ViewController.createResultController()

    private var fixUpdateContentOffset: CGPoint?

    override func viewDidLoad() {
        super.viewDidLoad()

        // Initial cells
        for i in 0...40 {
            let x = SomeEntity(context: CoreDataContext.persistentContainer.viewContext)

            x.something = randomString(length: i + 1)
            x.date = Date()
            x.height = Float.random(in: 50...100)
        }

        Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { (_) in
            let x = SomeEntity(context: CoreDataContext.persistentContainer.viewContext)

            x.something = self.randomString(length: Int.random(in: 10...50))
            x.date = Date()
            x.height = Float.random(in: 50...100)
        }

        resultController.delegate = self

        tableView.estimatedRowHeight = 75

        try! resultController.performFetch()
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        fixUpdateContentOffset = nil
    }

    override func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
        fixUpdateContentOffset = nil
    }

    override func scrollViewDidScroll(_ scrollView: UIScrollView) {
        if let fixUpdateContentOffset = fixUpdateContentOffset,
            tableView.contentOffset.y.rounded(.toNearestOrAwayFromZero) != fixUpdateContentOffset.y.rounded(.toNearestOrAwayFromZero) {
            tableView.contentOffset = fixUpdateContentOffset
        }
    }

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

    func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        fixUpdateContentOffset = tableView.contentOffset
        tableView.beginUpdates()
    }

    public func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        tableView.endUpdates()
        fixUpdateContentOffset = tableView.contentOffset
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return resultController.fetchedObjects?.count ?? 0
    }

    override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
        return CGFloat(resultController.object(at: indexPath).height)
    }

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)

        cell.textLabel?.text = resultController.object(at: indexPath).something

        return cell
    }


    private static func createResultController() -> NSFetchedResultsController<SomeEntity> {
        let fetchRequest: NSFetchRequest<SomeEntity> = SomeEntity.fetchRequest()

        fetchRequest.sortDescriptors = [NSSortDescriptor(key: "date", ascending: false)]

        return NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: CoreDataContext.persistentContainer.viewContext, sectionNameKeyPath: nil, cacheName: nil)
    }

    func randomString(length: Int) -> String {
        let letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
        return String((0...length-1).map{ _ in letters.randomElement()! })
    }
}

class CoreDataContext {
    static let persistentContainer: NSPersistentContainer =  {
        let container = NSPersistentContainer(name: "FetchViewControllerGlitch")

        container.loadPersistentStores(completionHandler: { (nsPersistentStoreDescription, error) in
            guard let error = error else {
                return
            }
            fatalError(error.localizedDescription)
        })

        return container
    }()
}