NSInternalInconsistencyException「理由是：」對-layoutAttributesForItemAtIndexPath沒有UICollectionViewLayoutAttributes例如，自定義佈局

Question

我有一個自定義的UICollectionLayout一個UICollectionView。這一切工作正常，直到我嘗試插入一行...

然後我得到以下錯誤，似乎無法找出如何解決它。

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'no UICollectionViewLayoutAttributes instance for -layoutAttributesForItemAtIndexPath: <NSIndexPath: 0xc000000000000016> {length = 2, path = 0 - 0}' 
*** First throw call stack: 
(
0 CoreFoundation      0x000000010915ae65 __exceptionPreprocess + 165 
1 libobjc.A.dylib      0x0000000108789deb objc_exception_throw + 48 
2 CoreFoundation      0x000000010915acca +[NSException raise:format:arguments:] + 106 
3 Foundation       0x000000010591a4de -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 198 
4 UIKit        0x00000001073e361c -[UICollectionViewData layoutAttributesForItemAtIndexPath:] + 627 
5 UIKit        0x00000001073a2859 __51-[UICollectionView _viewAnimationsForCurrentUpdate]_block_invoke1541 + 176 
6 UIKit        0x00000001073a02ed -[UICollectionView _viewAnimationsForCurrentUpdate] + 4524 
7 UIKit        0x00000001073a4a5c __62-[UICollectionView _updateWithItems:tentativelyForReordering:]_block_invoke1611 + 197 
8 UIKit        0x0000000106be01b8 +[UIView(Animation) performWithoutAnimation:] + 65 
9 UIKit        0x00000001073a3e07 -[UICollectionView _updateWithItems:tentativelyForReordering:] + 3241 
10 UIKit        0x000000010739eb98 -[UICollectionView _endItemAnimationsWithInvalidationContext:tentativelyForReordering:] + 15556 
11 UIKit        0x00000001073a5ee7 -[UICollectionView _performBatchUpdates:completion:invalidationContext:tentativelyForReordering:] + 415 
12 UIKit        0x00000001073a5d25 -[UICollectionView _performBatchUpdates:completion:invalidationContext:] + 74 
13 UIKit        0x00000001073a5cc8 -[UICollectionView performBatchUpdates:completion:] + 53 
14 Qanda        0x0000000103d9e0d9 _TFC5Qanda32HomeFeedCollectionViewController22redrawViewAfterNewDatafS0_FGSaCS_10QandaModel_T_ + 4105 
15 Qanda        0x0000000103dad5ca _TFFFC5Qanda32HomeFeedCollectionViewController9fetchDataFS0_FT_T_U_FTGSqGSaCS_10QandaModel__Sb_T_U0_FT_T_ + 1274 
16 Qanda        0x0000000103afc6b7 _TTRXFo__dT__XFdCb__dT__ + 39 
17 libdispatch.dylib     0x0000000109dd7e5d _dispatch_call_block_and_release + 12 
18 libdispatch.dylib     0x0000000109df849b _dispatch_client_callout + 8 
19 libdispatch.dylib     0x0000000109de02af _dispatch_main_queue_callback_4CF + 1738 
20 CoreFoundation      0x00000001090bad09 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9 
21 CoreFoundation      0x000000010907c2c9 __CFRunLoopRun + 2073 
22 CoreFoundation      0x000000010907b828 CFRunLoopRunSpecific + 488 
23 GraphicsServices     0x000000010c171ad2 GSEventRunModal + 161 
24 UIKit        0x0000000106b34610 UIApplicationMain + 171 
25 Qanda        0x0000000103bb537d main + 109 
26 libdyld.dylib      0x0000000109e2c92d start + 1 
) 
libc++abi.dylib: terminating with uncaught exception of type NSException 

這裏是我的佈局代碼：

var numberOfColumns: Int = 1 
let cellPadding: CGFloat = 10 
let buttonContainerHeight: CGFloat = 50 
let DEFAULT_HEIGHT: CGFloat = 80 

private var contentWidth: CGFloat = UIScreen.mainScreen().bounds.width 
private var totalContentHeight: CGFloat = 0.0 

// Delegate 
var delegate: HomeFeedCollectionViewLayoutDelegate? 


var cache = [UICollectionViewLayoutAttributes]() 


override func prepareLayout() { 

    // If cache is empty, calculate the layout 
    if cache.isEmpty { 
     // Set the size 
     let columnWidth = contentWidth/CGFloat(numberOfColumns) 
     var contentHeight: CGFloat = 0.0 
     var column = 0 
     let xOffset: CGFloat = 0 
     var yOffset: CGFloat = 0 
     var yOffsetArray = [CGFloat]() 

     // First check if sections actually exist 
     if collectionView!.numberOfSections() > 0 { 

      // Loop through items in section 
      for item in 0 ..< collectionView!.numberOfItemsInSection(0) { 

       let indexPath = NSIndexPath(forItem: item, inSection: 0) 
       let width = columnWidth - cellPadding * 2 

       let questionHeight = delegate?.collectionView(collectionView!, heightForQuestionAtIndexPath: indexPath, withWidth:width) 


       // Calculate frame 
       var height: CGFloat! 

       if questionHeight > 0 { 
        height = DEFAULT_HEIGHT + buttonContainerHeight + questionHeight! + 10 
       } 
       else { 
        height = contentWidth + buttonContainerHeight 
       } 


       if yOffsetArray.isEmpty { 
        log.debug("yOffsetArray is EMPTY") 
       } 
       else { 
        yOffset = yOffsetArray[item - 1] - cellPadding 
       } 

       yOffsetArray.append(height + yOffset) 


       let frame = CGRect(x: xOffset, y: yOffset, width: columnWidth, height: height) 
       let insetFrame = CGRectInset(frame, cellPadding, cellPadding) 

       // Create instance of UICollectionViewLayoutAttribute & set insetFrame 
       let attributes = UICollectionViewLayoutAttributes(forCellWithIndexPath: indexPath) 
       attributes.frame = insetFrame 
       cache.append(attributes) 

       // Make content height 
       contentHeight = contentHeight + (height - cellPadding) 

       column = column >= (numberOfColumns - 1) ? 0 : ++column 

      } 

      self.totalContentHeight = contentHeight 

     } 

    } 

} 


override func collectionViewContentSize() -> CGSize { 
    return CGSize(width: UIScreen.mainScreen().bounds.width, height: self.totalContentHeight + cellPadding) 
} 


override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? { 
    var layoutAttributes = [UICollectionViewLayoutAttributes]() 

    for attributes in cache { 
     if CGRectIntersectsRect(attributes.frame, rect) { 
      layoutAttributes.append(attributes) 
     } 
    } 
    return layoutAttributes 
} 

編輯：縮小錯誤的根源，好像回到只更新到如果正確的新值UICollectionViewLayoutAttributes CV首先被重新加載。但是，如果我這樣做了批處理更新會引發錯誤，說明AFTER之後的行數應該等於before加上插入的數字......這是有道理的。

編輯2：我現在很茫然。批量更新是否嘗試從默認佈局檢索佈局，而不是我的自定義佈局？

layoutAttributesForElementsInRect = [<UICollectionViewLayoutAttributes: 0x7ffc1d8baf70> index path: (<NSIndexPath: 0xc000000000000016> {length = 2, path = 0 - 0}); frame = (10 10; 355 405); , <UICollectionViewLayoutAttributes: 0x7ffc1d8a5930> index path: (<NSIndexPath: 0xc000000000200016> {length = 2, path = 0 - 1}); frame = (10 425; 355 143.222); , <UICollectionViewLayoutAttributes: 0x7ffc1d837240> index path: (<NSIndexPath: 0xc000000000400016> {length = 2, path = 0 - 2}); frame = (10 578.222; 355 143.222); [...] <UICollectionViewLayoutAttributes: 0x7ffc1d8d02f0> index path: (<NSIndexPath: 0xc000000002600016> {length = 2, path = 0 - 19}); frame = (10 3229.44; 355 143.222); ] 

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'no UICollectionViewLayoutAttributes instance for -layoutAttributesForItemAtIndexPath: <NSIndexPath: 0xc000000000200016> {length = 2, path = 0 - 1}' 

這怎麼可能？

Answer 1

對於那些誰遇到同樣的問題，我發現，當你做

self.collectionView?.performBatchUpdates({() -> Void in 
     // add new items into collection 
     self.collectionView?.insertItemsAtIndexPaths(indexPaths) 

     }, completion: { (finished) -> Void in 
      // do insertion animations 
    }); 

的layoutAttributesForElementsInRect方法不調用，layoutAttributesForItemAtIndexPath被稱爲替代。

因此，您還必須重寫layoutAttributesForItemAtIndexPath在自定義佈局，像這樣：

override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes? { 

    // Logic that calculates the UICollectionViewLayoutAttributes of the item 
    // and returns the UICollectionViewLayoutAttributes 
    return self.singleItemLayout(indexPath) 
} 

編輯：另外，如果遇到閃爍時，在它自己的批處理insertItemsAtIndexPaths方法。