crash in cellForRow : __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION

Question

I have the following crash report in my cellForRow method.

This is not something that I can reproduce myself when running through xCode.

Crashed: com.apple.main-thread
0  App                            0x1004a7624 specialized InspectionItemVC.tableView(UITableView, cellForRowAt : IndexPath) -> UITableViewCell (InspectionItemVC.swift:610)
1  App                           0x10049f82c @objc InspectionItemVC.tableView(UITableView, cellForRowAt : IndexPath) -> UITableViewCell (InspectionItemVC.swift)
2  UIKit                          0x198931d90 -[UITableView _createPreparedCellForGlobalRow:withIndexPath:willDisplay:] + 688
3  UIKit                          0x198931fa8 -[UITableView _createPreparedCellForGlobalRow:willDisplay:] + 80
4  UIKit                          0x19891f6ac -[UITableView _updateVisibleCellsNow:isRecursive:] + 2152
5  UIKit                          0x198936f98 -[UITableView _performWithCachedTraitCollection:] + 120
6  UIKit                          0x1986cf49c -[UITableView layoutSubviews] + 176
7  UIKit                          0x1985e9cc0 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1200
8  QuartzCore                     0x1957da274 -[CALayer layoutSublayers] + 148
9  QuartzCore                     0x1957cede8 CA::Layer::layout_if_needed(CA::Transaction*) + 292
10 UIKit                          0x1985fe458 -[UIView(Hierarchy) layoutBelowIfNeeded] + 548
11 UIKit                          0x1986a50c8 -[UINavigationController _layoutViewController:] + 1244
12 UIKit                          0x1986a2944 -[UINavigationController _layoutTopViewController] + 228
13 UIKit                          0x1986bb6f4 -[UINavigationController navigationTransitionView:didEndTransition:fromView:toView:] + 744
14 UIKit                          0x1986bb3d0 -[UINavigationTransitionView _notifyDelegateTransitionDidStopWithContext:] + 420
15 UIKit                          0x1986bafa0 -[UINavigationTransitionView _cleanupTransition] + 608
16 UIKit                          0x198625060 -[UIViewAnimationState sendDelegateAnimationDidStop:finished:] + 312
17 UIKit                          0x19862320c +[UIViewAnimationState popAnimationState] + 320
18 UIKit                          0x1986ae7dc -[UINavigationTransitionView transition:fromView:toView:] + 1860
19 UIKit                          0x1986a4764 -[UINavigationController _startTransition:fromViewController:toViewController:] + 2488
20 UIKit                          0x1986a3870 -[UINavigationController _startDeferredTransitionIfNeeded:] + 856
21 UIKit                          0x1986a3424 -[UINavigationController __viewWillLayoutSubviews] + 64
22 UIKit                          0x1986a3388 -[UILayoutContainerView layoutSubviews] + 188
23 UIKit                          0x1985e9cc0 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1200
24 QuartzCore                     0x1957da274 -[CALayer layoutSublayers] + 148
25 QuartzCore                     0x1957cede8 CA::Layer::layout_if_needed(CA::Transaction*) + 292
26 QuartzCore                     0x1957ceca8 CA::Layer::layout_and_display_if_needed(CA::Transaction*) + 32
27 QuartzCore                     0x19574a34c CA::Context::commit_transaction(CA::Transaction*) + 252
28 QuartzCore                     0x1957713ac CA::Transaction::commit() + 504
29 UIKit                          0x1985df308 _afterCACommitHandler + 256
30 CoreFoundation                 0x1924689a8 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 32
31 CoreFoundation                 0x192466630 __CFRunLoopDoObservers + 372
32 CoreFoundation                 0x192466a7c __CFRunLoopRun + 956
33 CoreFoundation                 0x192396da4 CFRunLoopRunSpecific + 424
34 GraphicsServices               0x193e01074 GSEventRunModal + 100
35 UIKit                          0x198651c9c UIApplicationMain + 208
36 App                            0x1000cfd04 main (AppDelegate.swift:22)
37 libdyld.dylib                  0x1913a559c start + 4

I read that the error in question is linked to NSNotificationCenter and that I need to remove my observer in viewWillDisappear.

I already had removed my observer in deinit and viewDidDisappear. If I add the removal of the observer to viewWillDisappear also, should this solve my issue?

Also if I add the observer removal to viewWillDisappear, should I get rid of this code in deinit and viewDidDisappear?

Previous code:

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    NotificationCenter.default.addObserver(self, selector:#selector(checkTimeout), name: NSNotification.Name(rawValue: "appOpened"), object: nil)
}

deinit {
    NotificationCenter.default.removeObserver(self)
}

override func viewDidDisappear(_ animated: Bool) {
    super.viewDidDisappear(animated);
    NotificationCenter.default.removeObserver(self)
}

override func viewWillDisappear(_ animated: Bool)
{
    //should I add NotificationCenter.default.removeObserver(self) here and remove it from the other two places above?
    if let answers = Helper_EQI_Answer.getAnswers(inspectionID)
    {
        inspection?.answers = answers;
    }
}

CellForRow snippet: I included the case of the switch statement that points to line 610. EQI_Question type is an enum. All cases are satisfied in the switch

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell
    {
        if let item: = insp_Questions?[indexPath.row]{

            if 1...12 ~= item.type && answerIDs != nil
            {
                switch (EQI_QuestionType(rawValue: item.type)!)
                {
                case .true_false:
                    if let cell = tableView.dequeueReusableCell(withIdentifier: "IQ_FlipCell") as? IQ_FlipCell
                    {
                        cell.table = questionTable;
                        cell.delegate = self;
                        cell.qID = answerIDs![indexPath.row];
                        cell.selectionStyle = .none
                        //this empty line is 610
                        if questionNA[indexPath.row]
                        {
                            cell.NABox.setImage(#imageLiteral(resourceName: "checkbox_selected"), for: .normal);
                            cell.questionItem.isHidden = true;
                        } else {
                            cell.NABox.setImage(#imageLiteral(resourceName: "checkbox_up"), for: .normal);
                            cell.questionItem.isHidden = false;
                        }

                        let cell2 = cell.formatCell(with: item, for: cell, at: indexPath, qtype: 0)
                        textHeight[indexPath.row] = cell.questionText.numberOfVisibleLines;
                        if item.question.characters.count > 40
                        {
                            textHeight[indexPath.row] += 1
                        }
                        return cell2;
                    }
                }
            }
         }
    return UITableViewCell();
}