将 UICollectionView 与 CoreData 和 NSFetchedResultsController 一起使用
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【中文标题】将 UICollectionView 与 CoreData 和 NSFetchedResultsController 一起使用【英文标题】：Using UICollectionView with CoreData and NSFetchedResultsController 【发布时间】：2015-06-19 07:59:43 【问题描述】：我最近开始了另一个项目，稍微探索一下 Swift。我想使用 NSFetchedResultsController 实现一个集合视图，以从我的 CoreData 数据库中获取数据。我想使用来自https://github.com/AshFurrow/UICollectionView-NSFetchedResultsController 的示例 并在 Swift 中实现类似的东西。我不需要任何移动事件，所以我实现了以下内容：
首先我创建了一个类来保存所做的更改：
class ChangeItem
var index:NSIndexPath
var type:NSFetchedResultsChangeType
init(index: NSIndexPath, type: NSFetchedResultsChangeType)
self.index = index
self.type = type
在我的集合视图控制器中，我使用两个数组来临时保存更改
var sectionChanges:[ChangeItem] = []
var objectChanges:[ChangeItem] = []
然后我等待我的 FetchedResultsController 在对 CoreData 数据库进行更改后进行更改
func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?,forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?)
var item:ChangeItem?
if(type == NSFetchedResultsChangeType.Insert)
item = ChangeItem(index: newIndexPath!, type: type)
else if(type == NSFetchedResultsChangeType.Delete)
item = ChangeItem(index: indexPath!, type: type)
else if(type == NSFetchedResultsChangeType.Update)
item = ChangeItem(index: indexPath!, type: type)
if(item != nil)
self.objectChanges.append(item!)
func controller(controller: NSFetchedResultsController, didChangeSection sectionInfo: NSFetchedResultsSectionInfo, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType)
var item:ChangeItem?
if(type == NSFetchedResultsChangeType.Insert || type == NSFetchedResultsChangeType.Delete || type == NSFetchedResultsChangeType.Update)
item = ChangeItem(index: NSIndexPath(forRow: 0, inSection: sectionIndex), type: type)
if(item != nil)
self.sectionChanges.append(item!)
应用所有更改后，FetchedResultsController 将执行 didChangeContent 方法
func controllerDidChangeContent(controller: NSFetchedResultsController)
println("something happened")
self.collectionView!.performBatchUpdates( () -> Void in
while(self.sectionChanges.count > 0 || self.objectChanges.count > 0)
self.insertSections()
self.insertItems()
self.updateItems()
let delips = self.deleteSections()
self.deleteItems(delips)
, completion: (done) -> Void in
if(done)
println("done")
self.collectionView.reloadData()
else
println("not done")
self.collectionView.reloadData()
if(self.fetchedResultsController.sections != nil && self.fetchedResultsController.sections?.count > 0)
println("number of items in first section \(self.fetchedResultsController.sections![0].count)")
)
self.deselectAll()
self.collectionView.reloadData()
if(self.fetchedResultsController.sections != nil && self.fetchedResultsController.sections!.count > 0)
for i in 1 ..< self.fetchedResultsController.sections!.count
if(self.fetchedResultsController.sections!.count > 0)
println(self.fetchedResultsController.sections![i].numberOfObjects )
然后再次调用以下方法
private func deleteSections()->NSIndexSet
var deletes = self.sectionChanges.filter( (item) -> Bool in
if(item.type == NSFetchedResultsChangeType.Delete)
let index = (self.sectionChanges as NSArray).indexOfObject(item)
self.sectionChanges.removeAtIndex(index)
return true
return false
) as [ChangeItem]
var indexSet:NSMutableIndexSet = NSMutableIndexSet()
for del in deletes
indexSet.addIndex(del.index.section)
if(indexSet.count > 0 && self.collectionView.numberOfSections() > 0)
self.collectionView.deleteSections(indexSet)
return indexSet
private func insertSections()
var inserts = self.sectionChanges.filter( (item) -> Bool in
if(item.type == NSFetchedResultsChangeType.Insert)
let index = (self.sectionChanges as NSArray).indexOfObject(item)
self.sectionChanges.removeAtIndex(index)
return true
return false
) as [ChangeItem]
var indexSet:NSMutableIndexSet = NSMutableIndexSet()
for ins in inserts
indexSet.addIndex(ins.index.section)
if(indexSet.count > 0)
println("Adding \(indexSet.count) section")
println(indexSet)
self.collectionView.insertSections(indexSet)
self.collectionView.reloadSections(indexSet)
private func deleteItems(deletedSections:NSIndexSet?)
var deletes = self.objectChanges.filter( (item) -> Bool in
if(item.type == NSFetchedResultsChangeType.Delete)
let index = (self.objectChanges as NSArray).indexOfObject(item)
self.objectChanges.removeAtIndex(index)
return true
return false
) as [ChangeItem]
var indexPaths:[NSIndexPath] = []
for del in deletes
if(del.index.section < self.fetchedResultsController.sections?.count)
if(deletedSections == nil || deletedSections!.containsIndex(del.index.section))
indexPaths.append(del.index)
/*indexPaths = indexPaths.sorted( (a, b) -> Bool in
if(a.section >= b.section && a.row >= b.row)
return true
return false
)
println(indexPaths)*/
//self.collectionView.numberOfItemsInSection(0)
if(indexPaths.count > 0)
println("deleting \(indexPaths.count) items")
self.collectionView.deleteItemsAtIndexPaths(indexPaths)
private func updateItems()
var updates = self.objectChanges.filter( (item) -> Bool in
if(item.type == NSFetchedResultsChangeType.Update)
let index = (self.objectChanges as NSArray).indexOfObject(item)
self.objectChanges.removeAtIndex(index)
return true
return false
) as [ChangeItem]
var indexPaths:[NSIndexPath] = []
for update in updates
indexPaths.append(update.index)
if(indexPaths.count > 0 )
println("did update on \(indexPaths.count) items")
self.collectionView.reloadItemsAtIndexPaths(indexPaths)
private func insertItems()
var inserts = self.objectChanges.filter( (item) -> Bool in
if(item.type == NSFetchedResultsChangeType.Insert)
let index = (self.objectChanges as NSArray).indexOfObject(item)
self.objectChanges.removeAtIndex(index)
return true
return false
) as [ChangeItem]
var indexPaths:[NSIndexPath] = []
for ins in inserts
indexPaths.append(ins.index)
if(indexPaths.count > 0 && self.numberOfSectionsInCollectionView(self.collectionView) > 0)
println("Adding \(indexPaths.count) items to collection view with \(self.collectionView.numberOfItemsInSection(0))")
self.collectionView.insertItemsAtIndexPaths(indexPaths)
println("Did add items")
一次删除多个项目和部分工作正常（现在），但插入一个部分不起作用。如您所见，我在 insertSections 方法中实现了一个输出。我的测试场景中的新部分的数量是 1，我得到了正确的 NSIndexSet 和 1 个项目：(0)。但是在 insertItems 方法中，我尝试在第 0 部分调用 numberOfObjects 并得到以下错误
*** Assertion failure in -[UICollectionViewData numberOfItemsInSection:], /SourceCache/UIKit_Sim/UIKit3347.44/UICollectionViewData.m:5942015-06-19:00:53:01.966 Grocli[42533:1547866] CoreData: error: Serious application error. An exception was caught from the delegate of NSFetchedResultsController during a call to -controllerDidChangeContent:. request for number of items in section 0 when there are only 0 sections in the collection view with userInfo (null)
提前感谢您阅读那篇长文并帮助我！
【问题讨论】：
【参考方案1】：这是我实现 FRC 委托方法的想法。
在这种情况下为 UICollectionViewController 子类：
斯威夫特 3
import UIKit
import CoreData
class FetchedResultsCollectionViewController: UICollectionViewController, NSFetchedResultsControllerDelegate
private var sectionChanges = [(type: NSFetchedResultsChangeType, sectionIndex: Int)]()
private var itemChanges = [(type: NSFetchedResultsChangeType, indexPath: IndexPath?, newIndexPath: IndexPath?)]()
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange sectionInfo: NSFetchedResultsSectionInfo, atSectionIndex sectionIndex: Int, for type: NSFetchedResultsChangeType)
sectionChanges.append((type, sectionIndex))
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?)
itemChanges.append((type, indexPath, newIndexPath))
func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>)
collectionView?.performBatchUpdates(
for change in self.sectionChanges
switch change.type
case .insert: self.collectionView?.insertSections([change.sectionIndex])
case .delete: self.collectionView?.deleteSections([change.sectionIndex])
default: break
for change in self.itemChanges
switch change.type
case .insert: self.collectionView?.insertItems(at: [change.newIndexPath!])
case .delete: self.collectionView?.deleteItems(at: [change.indexPath!])
case .update: self.collectionView?.reloadItems(at: [change.indexPath!])
case .move:
self.collectionView?.deleteItems(at: [change.indexPath!])
self.collectionView?.insertItems(at: [change.newIndexPath!])
, completion: finished in
self.sectionChanges.removeAll()
self.itemChanges.removeAll()
)
【讨论】：
当试图同时处理多个更新时，这可能会导致发生断言。我不得不将self.sectionChanges.removeAll() self.itemChanges.removeAll() 移动到主 performBatchUpdates 块中以避免这些问题。
是否需要同时使用controllerWillChangeContent方法清空2个变更列表？【参考方案2】：
听起来像是我不久前在使用客观 C 时遇到的问题。
退房
UICollectionView Assertion failure
我必须做一些工作才能让我的 FRC 与集合视图一起使用。
好像你找到了和我一样的 git，这里是解决集合视图问题的修复程序。
https://github.com/AshFurrow/UICollectionView-NSFetchedResultsController/issues/13
【讨论】：
Git 链接已被删除。总是发布一些必需的sn-p。我不赞成这个答案，因为这现在没用了。以上是关于将 UICollectionView 与 CoreData 和 NSFetchedResultsController 一起使用的主要内容，如果未能解决你的问题，请参考以下文章
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