'Nessuna istanza UICollectionViewLayoutAttributes per -layoutAttributesForItemAtIndexPath' errore utilizzando personalizzato UICollectionViewLayout

Question

sto usando un UICollectionViewLayout personalizzato come questo:

override func prepareLayout() { 
     cache.removeAll(keepCapacity: false) 

     let standardHeight = LayoutConstants.Cell.standardHeight 
     let featuredHeight = LayoutConstants.Cell.featuredHeight 

     var frame = CGRectZero 
     var y: CGFloat = 0 

     for item in 0..<numberOfItems { 
      let indexPath = NSIndexPath(forItem: item, inSection: 0) 
      let attributes = UICollectionViewLayoutAttributes(forCellWithIndexPath: indexPath) 
      let cell = collectionView!.cellForItemAtIndexPath(indexPath) 
      /* Important because each cell has to slide over the top of the previous one */ 
      attributes.zIndex = item 
      /* Initially set the height of the cell to the standard height */ 
      var height = standardHeight 
      if indexPath.item == featuredItemIndex { 
       /* The featured cell */ 
       let yOffset = standardHeight * nextItemPercentageOffset 
       y = collectionView!.contentOffset.y - yOffset 
       height = featuredHeight 
      } else if indexPath.item == (featuredItemIndex + 1) && indexPath.item != numberOfItems { 
       /* The cell directly below the featured cell, which grows as the user scrolls */ 
       let maxY = y + standardHeight 
       height = standardHeight + max((featuredHeight - standardHeight) * nextItemPercentageOffset, 0) 
       y = maxY - height 
      } 
      frame = CGRect(x: 0, y: y, width: width, height: height) 
      attributes.frame = frame 
      cache.append(attributes) 
      y = CGRectGetMaxY(frame) 
     } 
    } 

    /* Return all attributes in the cache whose frame intersects with the rect passed to the method */ 
    override func layoutAttributesForElementsInRect(rect: CGRect) -> [AnyObject]? { 
     var layoutAttributes = [UICollectionViewLayoutAttributes]() 
     for attributes in cache { 
      if CGRectIntersectsRect(attributes.frame, rect) { 
       layoutAttributes.append(attributes) 
      } 
     } 
     return layoutAttributes 
    } 

opere di Che come voglio, ma se voglio inserire un altro elemento, il mio incidente app con questo errore:

2015-05-31 22:37:29.032 Flore-Jessy[15359:717220] *** Assertion failure in -[UICollectionViewData layoutAttributesForItemAtIndexPath:], /SourceCache/UIKit_Sim/UIKit-3347.44/UICollectionViewData.m:694 
2015-05-31 22:37:29.077 Flore-Jessy[15359:717220] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'no UICollectionViewLayoutAttributes instance for -layoutAttributesForItemAtIndexPath: <NSIndexPath: 0x7b952a70> {length = 2, path = 0 - 15}' 
*** First throw call stack: 
(
    0 CoreFoundation      0x00a0a746 __exceptionPreprocess + 182 
    1 libobjc.A.dylib      0x02867a97 objc_exception_throw + 44 
    2 CoreFoundation      0x00a0a5da +[NSException raise:format:arguments:] + 138 
    3 Foundation       0x01093720 -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 118 
    4 UIKit        0x01de5c74 -[UICollectionViewData layoutAttributesForItemAtIndexPath:] + 461 
    5 UIKit        0x01dafbe7 __51-[UICollectionView _viewAnimationsForCurrentUpdate]_block_invoke1382 + 161 
    6 UIKit        0x01dad73b -[UICollectionView _viewAnimationsForCurrentUpdate] + 4789 
    7 UIKit        0x01db0eb8 -[UICollectionView _updateWithItems:tentativelyForReordering:] + 2447 
    8 UIKit        0x01dabf0d -[UICollectionView _endItemAnimationsWithInvalidationContext:tentativelyForReordering:] + 14802 
    9 UIKit        0x01da8536 -[UICollectionView _endItemAnimationsWithInvalidationContext:] + 48 
    10 UIKit        0x01da82ed -[UICollectionView _updateRowsAtIndexPaths:updateAction:] + 374 
    11 UIKit        0x01da833f -[UICollectionView insertItemsAtIndexPaths:] + 48 
    12 Flore-Jessy       0x0009183c _TFC11Flore_Jessy22TimelineViewController13viewDidAppearfS0_FSbT_ + 556 
    13 Flore-Jessy       0x000918cf _TToFC11Flore_Jessy22TimelineViewController13viewDidAppearfS0_FSbT_ + 63 
    14 UIKit        0x017f3245 -[UIViewController _setViewAppearState:isAnimating:] + 629 
    15 UIKit        0x017f3860 -[UIViewController __viewDidAppear:] + 171 
    16 UIKit        0x017f3b2b -[UIViewController _endAppearanceTransition:] + 322 
    17 UIKit        0x0180bd4e -[UIViewController(UIContainerViewControllerProtectedMethods) endAppearanceTransition] + 41 
    18 UIKit        0x017c403b -[UIPresentationController transitionDidFinish:] + 839 
    19 UIKit        0x01e50109 -[_UIFullscreenPresentationController transitionDidFinish:] + 59 
    20 UIKit        0x017c6c11 __56-[UIPresentationController runTransitionForCurrentState]_block_invoke_2 + 165 
    21 UIKit        0x01ef444a -[_UIViewControllerTransitionContext completeTransition:] + 124 
    22 Flore-Jessy       0x0008e174 _TFFC11Flore_Jessy29SwipeBluredTransitionAnimator17animateTransitionFS0_FPSo36UIViewControllerContextTransitioning_T_U0_FSbT_ + 436 
    23 Flore-Jessy       0x0008ca34 _TPA__TFFC11Flore_Jessy29SwipeBluredTransitionAnimator17animateTransitionFS0_FPSo36UIViewControllerContextTransitioning_T_U0_FSbT_ + 68 
    24 Flore-Jessy       0x0008e1bc _TTRXFo_dSb_dT__XFo_iSb_iT__ + 28 
    25 Flore-Jessy       0x0008caea _TPA__TTRXFo_dSb_dT__XFo_iSb_iT__ + 90 
    26 Flore-Jessy       0x0008e1f7 _TTRXFo_iSb_iT__XFo_dSb_dT__ + 39 
    27 Flore-Jessy       0x0008cb9e _TPA__TTRXFo_iSb_iT__XFo_dSb_dT__ + 78 
    28 Flore-Jessy       0x0008e245 _TTRXFo_dSb_dT__XFdCb_dV10ObjectiveC8ObjCBool_dT__ + 69 
    29 UIKit        0x017149be -[UIViewAnimationBlockDelegate _didEndBlockAnimation:finished:context:] + 318 
    30 UIKit        0x016f81b2 -[UIViewAnimationState sendDelegateAnimationDidStop:finished:] + 206 
    31 UIKit        0x016f8522 -[UIViewAnimationState animationDidStop:finished:] + 80 
    32 QuartzCore       0x0154a571 _ZN2CA5Layer23run_animation_callbacksEPv + 307 
    33 libdispatch.dylib     0x02f59bef _dispatch_client_callout + 14 
    34 libdispatch.dylib     0x02f3f6bb _dispatch_main_queue_callback_4CF + 993 
    35 CoreFoundation      0x009638ee __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 14 
    36 CoreFoundation      0x009215f0 __CFRunLoopRun + 2256 
    37 CoreFoundation      0x00920a5b CFRunLoopRunSpecific + 443 
    38 CoreFoundation      0x0092088b CFRunLoopRunInMode + 123 
    39 GraphicsServices     0x051e02c9 GSEventRunModal + 192 
    40 GraphicsServices     0x051e0106 GSEventRun + 104 
    41 UIKit        0x0168a106 UIApplicationMain + 1526 
    42 Flore-Jessy       0x00080a24 main + 180 
    43 libdyld.dylib      0x02f84ac9 start + 1 
) 
libc++abi.dylib: terminating with uncaught exception of type NSException 

questo è il codice che uso per inserire il nuovo elemento

override func viewDidAppear(animated: Bool) { 
     super.viewDidAppear(animated) 
     if let post = newPost { 

collectionView!.insertItemsAtIndexPaths([dataSource.indexPathForNewPost(post)]) 
     } 
    } 

/// Return the new indexPath for the TimelineItem 
    func indexPathForNewPost(item: TimelineItem) -> NSIndexPath { 
     if let liste = listPosts { 
      listPosts!.append(item) 
     } 
     return indexPathForPost(item) 
    } 

    func indexPathForPost(item: TimelineItem) -> NSIndexPath { 
     var itemIndex = 0 
     for (index, currentTimelineItem) in enumerate(allPosts()) { 
      if currentTimelineItem === item { 
       itemIndex = index 
       break 
      } 
     } 
     return NSIndexPath(forItem: itemIndex, inSection: 0) 
    } 

Qualche idea?

Answer 1

In base al messaggio di errore, ciò è dovuto al fatto che la cella non può recuperare layoutAttributes. layoutAttributesForItemAtIndexPath restituisce nil se la cella che verrà creata dall'aggiornamento non è visibile.

Per correggere questo errore, eseguire l'override layoutAttributesForItemAtIndexPath metodo:

override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes? { 
     return cache[indexPath.row] 
    } 

SWIFT 3 -

override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? { 
    return cache[indexPath.row] 
    }