我有一个带有自定义UICollectionLayout的UICollectionView.这一切都很好,直到我尝试插入一行…
*** 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
这是我的布局代码：
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 }
编辑：缩小错误的根源,似乎返回的UICollectionViewLayoutAttributes仅在首先重新加载CV时才更新为正确的新值.但是,如果我这样做,批量更新会抛出一个错误,说明AFTER的总行数应该等于之前加上插入的数字……这是有道理的.
编辑2：现在我不知所措.批量更新是否尝试从默认布局检索布局而不是我的自定义布局？
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}'
这怎么可能？
对于那些遇到同样问题的人,我发现当你这样做时
self.collectionView?.performBatchUpdates({ () -> Void in
// add new items into collection
self.collectionView?.insertItemsAtIndexPaths(indexPaths)
},completion: { (finished) -> Void in
// do insertion animations
});
不调用layoutAttributesForElementsInRect方法,而是调用layoutAttributesForItemAtIndexPat.
因此,您还必须在自定义布局中覆盖layoutAttributesForItemAtIndexPath,如下所示：
override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes? {
// Logic that calculates the UICollectionViewLayoutAttributes of the item
// and returns the UICollectionViewLayoutAttributes
return self.singleItemLayout(indexPath)
}
编辑：另外,如果您在批量insertItemsAtIndexPaths方法上遇到闪烁,那就是它自己.
