ios - 'No UICollectionViewLayoutAttributes instance for -layoutAttributesForItemAtIndexPath' error using custom UICollectionViewLayout -

i'm using custom uicollectionviewlayout :

override func preparelayout() {         cache.removeall(keepcapacity: false)          let standardheight = layoutconstants.cell.standardheight         let featuredheight = layoutconstants.cell.featuredheight          var frame = cgrectzero         var y: cgfloat = 0          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 slide on top of previous 1 */             attributes.zindex = item             /* set height of cell standard height */             var height = standardheight             if indexpath.item == featureditemindex {                 /* featured cell */                 let yoffset = standardheight * nextitempercentageoffset                 y = collectionview!.contentoffset.y - yoffset                 height = featuredheight             } else if indexpath.item == (featureditemindex + 1) && indexpath.item != numberofitems {                 /* cell directly below featured cell, grows 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 attributes in cache frame intersects rect passed method */     override func layoutattributesforelementsinrect(rect: cgrect) -> [anyobject]? {         var layoutattributes = [uicollectionviewlayoutattributes]()         attributes in cache {             if cgrectintersectsrect(attributes.frame, rect) {                 layoutattributes.append(attributes)             }         }         return layoutattributes     } 

that's works want if wanna insert other item, app crash error :

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 uncaught exception 'nsinternalinconsistencyexception', reason: 'no uicollectionviewlayoutattributes instance -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 uncaught exception of type nsexception 

this code use insert new item

override func viewdidappear(animated: bool) {         super.viewdidappear(animated)         if let post = newpost {  collectionview!.insertitemsatindexpaths([datasource.indexpathfornewpost(post)])         }     }  /// return new indexpath timelineitem     func indexpathfornewpost(item: timelineitem) -> nsindexpath {         if let liste = listposts {             listposts!.append(item)         }         return indexpathforpost(item)     }      func indexpathforpost(item: timelineitem) -> nsindexpath {         var itemindex = 0         (index, currenttimelineitem) in enumerate(allposts()) {             if currenttimelineitem === item {                 itemindex = index                 break             }         }         return nsindexpath(foritem: itemindex, insection: 0)     } 

any idea ?

base on error message, because of cell can't retrieve layoutattributes. layoutattributesforitematindexpath returns nil if cell created update not visible.

to fix error, override layoutattributesforitematindexpath method:

override func layoutattributesforitematindexpath(indexpath: nsindexpath) -> uicollectionviewlayoutattributes? {         return cache[indexpath.row]     } 

swift 3 -

override func layoutattributesforitem(at indexpath: indexpath) -> uicollectionviewlayoutattributes? {     return cache[indexpath.row]   }