我读过其他一些关于此问题的问题，这些问题与 CollectionView 的大小有关。我已经尝试按照这些答案中的建议调整大小，但它们都不起作用。我正在使用 NSFetchedResultsController ，它也为我进行了卷积(我想知道它是否与不触发有关)。
无论如何，真正的问题是我的 UICollectionView 没有显示任何内容。运行时没有错误，只是黑屏。我正在 Swift 中工作(显然)。
这是我在 ViewController 中的代码:
import UIKit
import CoreData
private let reuseIdentifier = "Family"
private var selectedFirstName:String = "Blank"
private var selectedLastName:String = "Blank"
private var selectedNumber:String = "Blank"
private var selectedEmail:String = "Blank"
class FamilyViewController: UIViewController, UICollectionViewDataSource {
var coreDataStack: CoreDataStack!
var fetchedResultsController: NSFetchedResultsController!
@IBOutlet var familyCollectionView: UICollectionView!
override func viewDidLoad() {
super.viewDidLoad()
//1
let fetchRequest = NSFetchRequest(entityName: "Family")
let firstNameSort =
NSSortDescriptor(key: "firstName", ascending: true)
fetchRequest.sortDescriptors = [firstNameSort]
//2
self.coreDataStack = CoreDataStack()
fetchedResultsController =
NSFetchedResultsController(fetchRequest: fetchRequest,
managedObjectContext: coreDataStack.context,
sectionNameKeyPath: nil,
cacheName: nil)
fetchedResultsController.delegate = CollectionViewFetchedResultsControllerDelegate(collectionView: familyCollectionView)
//3
do {
try fetchedResultsController.performFetch()
} catch let error as NSError {
print("Error: \(error.localizedDescription)")
}
}
func configureCell(cell: FamilyCCell, indexPath: NSIndexPath) { let family = fetchedResultsController.objectAtIndexPath(indexPath) as! Family
cell.firstNameLabel.text = family.firstName
print("configureCell ran")
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
// #warning Incomplete implementation, return the number of sections
print("numberOfSectionsInCollectionView ran")
return fetchedResultsController.sections!.count
}
func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
// #warning Incomplete implementation, return the number of items
let sectionInfo = fetchedResultsController.sections![section]
print("numberOfItemsInSection ran")
return sectionInfo.numberOfObjects
}
func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCellWithReuseIdentifier(reuseIdentifier, forIndexPath: indexPath) as! FamilyCCell
print("cellForItemAtIndexPath ran")
configureCell(cell, indexPath: indexPath)
return cell
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if (segue.identifier == "showDetail") {
let detailVC = segue.destinationViewController as! ContactViewController
print("prepareForSegue ran")
detailVC.detailFirstName = selectedFirstName
detailVC.detailLastName = selectedLastName
detailVC.detailNumber = selectedNumber
detailVC.detailEmail = selectedEmail
}
}
}
extension FamilyViewController: UICollectionViewDelegate {
func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
print("didSelectItemAtIndexPath ran")
collectionView.delegate = self
let family = fetchedResultsController.objectAtIndexPath(indexPath) as! Family
selectedFirstName = family.firstName!
selectedLastName = family.lastName!
selectedNumber = family.phone!
selectedEmail = family.email!
coreDataStack.saveContext()
}
}
class CollectionViewFetchedResultsControllerDelegate: NSObject, NSFetchedResultsControllerDelegate {
// MARK: Properties
private let collectionView: UICollectionView
private var blockOperations: [NSBlockOperation] = []
// MARK: Init
init(collectionView: UICollectionView) {
self.collectionView = collectionView
}
// MARK: Deinit
deinit {
blockOperations.forEach { $0.cancel() }
blockOperations.removeAll(keepCapacity: false)
}
// MARK: NSFetchedResultsControllerDelegate
func controllerWillChangeContent(controller: NSFetchedResultsController) {
blockOperations.removeAll(keepCapacity: false)
}
func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {
switch type {
case .Insert:
guard let newIndexPath = newIndexPath else { return }
let op = NSBlockOperation { [weak self] in self?.collectionView.insertItemsAtIndexPaths([newIndexPath]) }
blockOperations.append(op)
case .Update:
guard let newIndexPath = newIndexPath else { return }
let op = NSBlockOperation { [weak self] in self?.collectionView.reloadItemsAtIndexPaths([newIndexPath]) }
blockOperations.append(op)
case .Move:
guard let indexPath = indexPath else { return }
guard let newIndexPath = newIndexPath else { return }
let op = NSBlockOperation { [weak self] in self?.collectionView.moveItemAtIndexPath(indexPath, toIndexPath: newIndexPath) }
blockOperations.append(op)
case .Delete:
guard let indexPath = indexPath else { return }
let op = NSBlockOperation { [weak self] in self?.collectionView.deleteItemsAtIndexPaths([indexPath]) }
blockOperations.append(op)
}
}
func controller(controller: NSFetchedResultsController, didChangeSection sectionInfo: NSFetchedResultsSectionInfo, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType) {
switch type {
case .Insert:
let op = NSBlockOperation { [weak self] in self?.collectionView.insertSections(NSIndexSet(index: sectionIndex)) }
blockOperations.append(op)
case .Update:
let op = NSBlockOperation { [weak self] in self?.collectionView.reloadSections(NSIndexSet(index: sectionIndex)) }
blockOperations.append(op)
case .Delete:
let op = NSBlockOperation { [weak self] in self?.collectionView.deleteSections(NSIndexSet(index: sectionIndex)) }
blockOperations.append(op)
default: break
}
}
func controllerDidChangeContent(controller: NSFetchedResultsController) {
collectionView.performBatchUpdates({
self.blockOperations.forEach { $0.start() }
}, completion: { finished in
self.blockOperations.removeAll(keepCapacity: false)
})
}
}
我有打印语句确认 cellForItemAtIndexPath 未运行。有任何想法吗？我意识到这是非常具体的，我给出了大量代码，只是不太确定错误可能来自哪里。感谢您提前提供的任何帮助。
最佳答案
确保...您确认 UICollectionViewDelegate 协议(protocol)方法。
设置 collectionview.delegate = self
collectionview.datasource = self
关于ios - 未调用 cellForItemAtIndexPath，原因不明，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/35775621/