UITableview reloadRowsAtIndexPaths and crash - ios

Question

I have code like this. When I debug with exception breakpoint, it crash when I reloadRow.
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
if (section == 0)
return ceil(self.folders.count/ 2);
else if (section <= self.documents.count) {
DocumentsCollection *dc = self.documents[section - 1];
return dc.attachments.count;
}
return 0;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
//..........
[cell setData:dc.attachments[indexPath.row] andReload:^{
[tableView reloadRowsAtIndexPaths:#[indexPath] withRowAnimation:UITableViewRowAnimationNone];
}];
}
I am using constraint in my cell and all my data are really correct. I am trying to read error message and find in here too but I don't get it. Please kindly explain how I shall do. I totally don't understand why it say
"reason: '*** -[__NSArrayM objectAtIndex:]: index 4 beyond bounds [0 .. 3]'"
*** First throw call stack:
(
0 CoreFoundation 0x000000011334fd4b __exceptionPreprocess + 171
1 libobjc.A.dylib 0x000000011252d21e objc_exception_throw + 48
2 CoreFoundation 0x00000001132812eb -[__NSArrayM objectAtIndex:] + 203
3 UIKit 0x0000000110c61df6 -[UITableView _existingCellForRowAtIndexPath:] + 159
4 UIKit 0x0000000110c8555c -[UITableView _heightForRowAtIndexPath:] + 109
5 UIKit 0x0000000110ebd783 -[UISectionRowData heightForRow:inSection:canGuess:] + 263
6 UIKit 0x0000000110ec5601 -[UITableViewRowData rectForRow:inSection:heightCanBeGuessed:] + 1016
7 UIKit 0x0000000110ec5707 -[UITableViewRowData rectForGlobalRow:heightCanBeGuessed:] + 142
8 UIKit 0x0000000110ec64b9 -[UITableViewRowData globalRowsInRect:canGuess:] + 1101
9 UIKit 0x0000000110fa5cf3 -[_UITableViewUpdateSupport(Private) _visibleRowRangePlusAdjoining] + 96
10 UIKit 0x0000000110fa5dc8 -[_UITableViewUpdateSupport(Private) _faultInRealHeightsOfNeededCells] + 138
11 UIKit 0x0000000110fb81c7 -[_UITableViewUpdateSupport _setupAnimations] + 164
12 UIKit 0x0000000110c544dd -[UITableView _updateWithItems:updateSupport:] + 3054
13 UIKit 0x0000000110c4c90f -[UITableView _endCellAnimationsWithContext:] + 17960
14 UIKit 0x0000000110c63f62 -[UITableView _updateRowsAtIndexPaths:updateAction:withRowAnimation:] + 331
15 UIKit 0x0000000126e4d4a2 -[UITableViewAccessibility reloadRowsAtIndexPaths:withRowAnimation:] + 73
16 iFeedback 0x000000010dc809ad __56-[DocumentVCWithFolder tableView:cellForRowAtIndexPath:]_block_invoke + 125
17 iFeedback 0x000000010dbeb6e8 -[DocumentDetailCell observeValueForKeyPath:ofObject:change:context:] + 552
18 Foundation 0x000000010f25bdec NSKeyValueNotifyObserver + 351
19 Foundation 0x000000010f25b687 NSKeyValueDidChange + 495
20 Foundation 0x000000010f33cb95 -[NSObject(NSKeyValueObservingPrivate) _changeValueForKeys:count:maybeOldValuesDict:usingBlock:] + 986
21 Foundation 0x000000010f220b01 -[NSObject(NSKeyValueObservingPrivate) _changeValueForKey:key:key:usingBlock:] + 60
22 Foundation 0x000000010f2e80df _NSSetSizeValueAndNotify + 285
23 UIKit 0x000000011144fa84 -[UICollectionView _updateVisibleCellsNow:] + 745
24 UIKit 0x0000000111456725 -[UICollectionView layoutSubviews] + 313
25 UIKit 0x0000000110bd2ab8 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1237
26 QuartzCore 0x00000001106e6bf8 -[CALayer layoutSublayers] + 146
27 QuartzCore 0x00000001106da440 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 366
28 UIKit 0x0000000110bc0928 -[UIView(Hierarchy) layoutBelowIfNeeded] + 1509
29 iFeedback 0x000000010dbeb4a9 -[DocumentDetailCell setUpTag] + 553
30 iFeedback 0x000000010dbeb24a -[DocumentDetailCell setData:andReload:] + 154
31 iFeedback 0x000000010dc8078b -[DocumentVCWithFolder tableView:cellForRowAtIndexPath:] + 1995
32 UIKit 0x0000000110c7b584 -[UITableView _createPreparedCellForGlobalRow:withIndexPath:willDisplay:] + 757
33 UIKit 0x0000000110c7b7e2 -[UITableView _createPreparedCellForGlobalRow:willDisplay:] + 74
34 UIKit 0x0000000110c4f2b0 -[UITableView _updateVisibleCellsNow:isRecursive:] + 3295
35 UIKit 0x0000000110c84b64 -[UITableView _performWithCachedTraitCollection:] + 110
36 UIKit 0x0000000110c6b3be -[UITableView layoutSubviews] + 222
37 UIKit 0x0000000110bd2ab8 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1237
38 QuartzCore 0x00000001106e6bf8 -[CALayer layoutSublayers] + 146
39 QuartzCore 0x00000001106da440 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 366
40 QuartzCore 0x00000001106da2be _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 24
41 QuartzCore 0x0000000110668318 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 280
42 QuartzCore 0x00000001106953ff _ZN2CA11Transaction6commitEv + 475
43 QuartzCore 0x0000000110695d6f _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 113
44 CoreFoundation 0x00000001132f4267 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
45 CoreFoundation 0x00000001132f41d7 __CFRunLoopDoObservers + 391
46 CoreFoundation 0x00000001132d8f8e __CFRunLoopRun + 1198
47 CoreFoundation 0x00000001132d8884 CFRunLoopRunSpecific + 420
48 GraphicsServices 0x0000000115340a6f GSEventRunModal + 161
49 UIKit 0x0000000110b0dc68 UIApplicationMain + 159
50 iFeedback 0x000000010dc60ebf main + 111
51 libdyld.dylib 0x00000001138da68d start + 1
)

Answer 1

I believe the Array the error is referring to is actually the queue of reusable cells that the UITableView maintain. When you call reloadRowsAtIndexPath, the tableView will ask its delegate for another cell at the same indexPath.
By adding a log into the first and last line of cellForRowAtIndexPath my log look something like:
Start for cell at [0, 9]
Start for cell at [0, 9]
End for cell at [0, 9]
End for cell at [0, 9]
Start for cell at [0, 10]
Start for cell at [0, 10]
End for cell at [0, 10]
End for cell at [0, 10]
Start for cell at [1, 0]
Start for cell at [1, 0]
End for cell at [1, 0]
End for cell at [1, 0]
Start for cell at [1, 1]
2017-01-10 16:48:05.530 TableView[25012:201598] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 8 beyond bounds [0 .. 7]'
which shows that if the completion handler of your setData gets called before the cellForRowAtIndexPath completes, your UITableView will attempt to call for one more cell then it has - note that my error says index 8 beyond bounds [0 .. 7] and my UITableView has got 8 visible cells.
To solve the problem, I suggest not calling reloadRowAtIndexPath but instead update the values of whatever display your cell contains directly.

Answer 2

your code is showing error because the block in which you are setting the data might be giving little bit delay.
The summary of what i meant is that you are reloading the table view from its delegate method. And the reloading is getting called from a block which might be the reason of crash.
You can do one thing, rather then reloading specific row, try to reload whole table.
Hope it will work.

Answer 3

Keep it simple.
Number of Row in every section should equal to objects in Array.
Suppose you pass 4 count in section 1 (which starts at index == 0) should equal to your Array objects.
It is crashing due to ROW count and Object in array is not matching.
If it not matched than you will get
"reason: '* -[__NSArrayM objectAtIndex:]: index 4 beyond bounds [0 .. 3]'"
Bounds [0..3] means Array has only 4 objects and it is trying to get 5th object at index 4.
Please check it and should has proper count in Array object.