我正在尝试使用NSFetchedResultsController / NSFetchedResultsControllerDelegate更新UICollectionView。 UPDATE UICollectionView有21个单元格，每行有3个单元格。
我的想法是我正在下载一些图像数据，我将它们保存在BackgroundContext上的CoreData上
(backgroundContext = NSManagedObjectContext(concurrencyType:.privateQueueConcurrencyType)
backgroundContext.parent = context)
context = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
当我下载并保存在backgroundContext上数据时，我正在加载一个带有UICollectionView的新Controller，我正在获取他们将要保存在backgroundContext上的数据，而backgroundContext将会告知新数据的上下文，并使用NSFetchedResultsControllerDelegate函数，我将更新我的UICollectionViewCells。
更新每次从API下载的imageData为21。
保存
stack!.backgroundContext.perform({
let photoFrame = PhotoFrame(pin: pin, imageData: imageData as NSData, context: self.stack!.backgroundContext)
do{
try self.stack!.backgroundContext.save()
print("OK Saved Background")
}catch{
print("Error background saving")
}
})
一切都很好我得到了数据存储！
NSFetchedResultsControllerDelegate
func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
insertIndexPaths = [IndexPath]()
deleteIndexPaths = [IndexPath]()
updateIndexPaths = [IndexPath]()
print("*** controller will change content")
}
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
switch type{
case .insert:
print("Insert an item newIndexPath : \(newIndexPath!)")
self.insertIndexPaths.append(newIndexPath!)
case .delete:
print("Delete an Item")
deleteIndexPaths.append(indexPath!)
case .update:
print("Update an item")
updateIndexPaths.append(indexPath!)
case .move:
print("move")
}
}
func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
collectionView.performBatchUpdates({
for indexPath in self.insertIndexPaths {
print("Inserting FetchedObjects at: \(indexPath)")
self.collectionView.insertItems(at: [indexPath])
}
for indexPath in self.deleteIndexPaths {
self.collectionView.deleteItems(at: [indexPath])
}
for indexPath in self.updateIndexPaths{
self.collectionView.reloadItems(at: [indexPath])
}
}, completion: {finished in
print("Finished")
})
}
我正在使用此功能加载单元格
ConfigureCell
cell.activityIndicator.startAnimating()
cell.collectionImageView.image = UIImage(named: "placeholder")
if frc!.fetchedObjects!.count > 0 {
if cell.collectionImageView.image == UIImage(named: "placeholder") {
print("IndexPath: \(indexPath)")
print("fetchedObjects : \(frc!.fetchedObjects!.count)")
if let photoFrame = frc!.object(at: indexPath) as? PhotoFrame{
cell.collectionImageView.image = UIImage(data:(photoFrame.imageData! as NSData) as Data)
cell.activityIndicator.stopAnimating()
cell.activityIndicator.isHidden = true
}
}
}
一切正常但是在NSFetchedResultsControllerDelegate函数
func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>)
当我运行应用程序时，我得到了这个奇怪的输出：
*** controller will change content
Insert an item newIndexPath : [0, 0]
Inserting FetchedObjects at: [0, 0]
IndexPath: [0, 0]
fetchedObjects : 1
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 0]
Inserting FetchedObjects at: [0, 0]
IndexPath: [0, 0]
fetchedObjects : 2
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 0]
Inserting FetchedObjects at: [0, 0]
IndexPath: [0, 0]
fetchedObjects : 3
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 1]
Inserting FetchedObjects at: [0, 1]
IndexPath: [0, 1]
fetchedObjects : 4
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 1]
Inserting FetchedObjects at: [0, 1]
IndexPath: [0, 1]
fetchedObjects : 5
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 2]
Inserting FetchedObjects at: [0, 2]
IndexPath: [0, 2]
fetchedObjects : 6
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 2]
Inserting FetchedObjects at: [0, 2]
IndexPath: [0, 2]
fetchedObjects : 7
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 3]
Inserting FetchedObjects at: [0, 3]
IndexPath: [0, 3]
fetchedObjects : 8
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 3]
Inserting FetchedObjects at: [0, 3]
IndexPath: [0, 3]
fetchedObjects : 9
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 4]
Inserting FetchedObjects at: [0, 4]
IndexPath: [0, 4]
fetchedObjects : 10
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 4]
Inserting FetchedObjects at: [0, 4]
IndexPath: [0, 4]
fetchedObjects : 11
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 5]
Inserting FetchedObjects at: [0, 5]
IndexPath: [0, 5]
fetchedObjects : 12
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 5]
Inserting FetchedObjects at: [0, 5]
IndexPath: [0, 5]
fetchedObjects : 13
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 6]
Inserting FetchedObjects at: [0, 6]
IndexPath: [0, 6]
fetchedObjects : 14
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 6]
Inserting FetchedObjects at: [0, 6]
IndexPath: [0, 6]
fetchedObjects : 15
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 7]
Inserting FetchedObjects at: [0, 7]
IndexPath: [0, 7]
fetchedObjects : 16
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 7]
Inserting FetchedObjects at: [0, 7]
IndexPath: [0, 7]
fetchedObjects : 17
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 8]
Inserting FetchedObjects at: [0, 8]
IndexPath: [0, 8]
fetchedObjects : 18
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 8]
Inserting FetchedObjects at: [0, 8]
IndexPath: [0, 8]
fetchedObjects : 19
OK Saved Background
*** controller will change content
Insert an item newIndexPath : [0, 9]
Inserting FetchedObjects at: [0, 9]
IndexPath: [0, 9]
fetchedObjects : 20
OK Saved Background
Success
*** controller will change content
Insert an item newIndexPath : [0, 9]
Inserting FetchedObjects at: [0, 9]
IndexPath: [0, 9]
fetchedObjects : 21
OK Saved Background
任何想法为什么我在.insert（newIndexPath！）上复制indexPaths？