我使用CoreData
与NSFetchResultController
有一个UITableView
显示的数据。我有一个问题:UITableView
的变化时插入一个新的行/移动/删除的contentOffSet.y
。当用户已滚动于,例如中间,当插入新行的UITableView
反弹。
这github上链接到一个项目,该项目包含最小代码重现此问题:https://github.com/Jasperav/FetchResultControllerGlitch(代码是向下跌破以及)
这正显示出毛刺。我站在我的UITableView
的中间,我不断看到新行插入,而不考虑当前contentOffSet.y
的:
rowHeight
和estimatedRowHeight
。endUpdates
品尝过rowHeight
和estimatedRowHeight
。我也试着开关performBatchUpdates
而不是begin/endUpdates
,未制定出也。
该UITableView
插入时/删除/移动行时的行不是对用户可见的只是应保持不动。我希望这样的事情应该只是工作开箱。
这就是我最终想要的(刚刚的WhatsApp的聊天画面的复制):
UITableView
应动画新插入的行和更改当前contentOffSet.y
。如果UICollectionView
会是更好的选择,这将是罚款。
我试图复制WhatsApp的聊天屏幕。我不知道,如果他们使用NSFetchResultController,但除此之外,最终的目标是为他们提供准确的用户体验。所以插入,移动,删除和更新细胞应该做的WhatsApp是做它的方式。因此,对于一个工作示例:去WhatsApp的,对于一个没有工作的例子:下载该项目。
代码(ViewController.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
}()
}
let lastScrollOffset = tableView.contentOffset;
tableView.beginUpdates();
tableView.insertRows(at: [newIndexPath!], with: .automatic);
tableView.endUpdates();
tableView.layer.removeAllAnimations();
tableView.setContentOffset(lastScrollOffset, animated: false);
您还可以检查此tutorial
我已经成功地做到这一点。
缺点是禁用取还禁用或更新现有的行删除。取重启后这些变化将被应用。
我也尝试对controller(_:didChange:at:for:newIndexPath:)
调整contentOffset但它并没有在所有的工作。
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
}()
}
做这个
tableView.bounces = false
它会工作
第1步:定义你所说的“不动”的意思。对于人类来说这是很清楚的,它是跳跃。但是电脑看到了contentOffset是保持相同。所以,让我们非常精确,并定义具有明显的顶部的第一个单元格应该在那里变更后留下准确。所有其他细胞可以左右移动,但是这是我们的锚。
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
}
}
}
当我们调用setAnchorPoint
我们发现并记住哪个实体(不indexPath
因为这可能会改变短期)接近顶部,从顶部它究竟有多远。
接下来让我们称之为setAnchorPoint
变化发生前的权利:
func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
self.setAnchorPoint()
tableView.beginUpdates()
}
且其变动完成后,我们滚动回到我们的假设是没有任何动画:
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)
}
}
}
这就是它!这不会做你的时候,当视图是完全滚动到顶部,但我相信你可以自己处理这种情况。
你可以试试这个它上面POOJA的回答一个编辑,我所面临的问题像你这样的UIView.performWithoutAnimation消除了me.Hope它有助于问题。
UIView.performWithoutAnimation {
let lastScrollOffset = tableView.contentOffset;
tableView.beginUpdates();
tableView.insertRows(at: [newIndexPath!], with: .automatic);
tableView.endUpdates();
tableView.setContentOffset(lastScrollOffset, animated: false);
}
编辑
你也可以尝试上述但不是插入行,你可以使用重载数据上的tableview但在这之前获取的数据添加到您的数据源,并设置块内的最后contentoffeset。
表视图是一个复杂的野兽。它的行为不同,这取决于它的配置。表视图调整内容时插入,更新,删除和移动的行偏移。如果表视图表格视图控制器内使用的滚动视图的委托方法scrollViewDidScroll(_ :)被调用。
该解决方案是撤销内容偏移调整在那里。然而,这是对表视图的意图,因此需要做几次,直到viewDidLayoutSubviews()被调用。所以,解决的办法是不是最佳的,但它的工作原理与动力高度的细胞,章节标题,页脚部分,并应符合你的目标。
对于解决办法,我已经重建你的代码。您的视图控制器不再基于UIViewController的,但上的UITableViewController。该解决方案的重要组成部分是治疗和使用该属性fixUpdateContentOffset的。
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
}()
}