App crashes when number of rows changes after reloading table - ios

Question

In my iOS app there is a view with a tableview inside. The table cells are loaded from a PHP file on a remote server. I have also put a NSTimer on the view controller that should reload the data.
The cells contain information that may change on a time interval. That is working fine only if the number of cells doesn't change on a time interval. If a cell is added on a time interval, then the app crashes.
This is the code for the NSTimer:
self.timer = [NSTimer scheduledTimerWithTimeInterval:10 target:self selector:#selector(refrescar) userInfo:nil repeats:YES];
And this is the code for the method refrescar:
- (void)refrescar {
total_actual =0;
total =0;
[self viewDidLoad];
}
I have also tried with this one:
- (void)refrescar {
total_actual =0;
total =0;
[self.tableView reloadData];
}
But the app crashes as with the other code with [self viewDidLoad];
Any help is welcome.
Error log:
2014-11-13 23:52:23.299 RestAppXXI[1552:607] -[NSNull length]: unrecognized selector sent to instance 0xcb6068
2014-11-13 23:52:23.429 RestAppXXI[1552:607] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSNull length]: unrecognized selector sent to instance 0xcb6068'
*** First throw call stack:
(
0 CoreFoundation 0x00b6a1e4 __exceptionPreprocess + 180
1 libobjc.A.dylib 0x031588e5 objc_exception_throw + 44
2 CoreFoundation 0x00c07243 -[NSObject(NSObject) doesNotRecognizeSelector:] + 275
3 CoreFoundation 0x00b5a50b ___forwarding___ + 1019
4 CoreFoundation 0x00b5a0ee _CF_forwarding_prep_0 + 14
5 UIKit 0x01fd2cc7 -[UILabel _textRectForBounds:limitedToNumberOfLines:includingShadow:] + 57
6 UIKit 0x01fd2b13 -[UILabel textRectForBounds:limitedToNumberOfLines:] + 85
7 UIKit 0x01fd662e -[UILabel _intrinsicSizeWithinSize:] + 173
8 UIKit 0x01fd6751 -[UILabel intrinsicContentSize] + 91
9 UIKit 0x024b07ef -[UIView(UIConstraintBasedLayout) _generateContentSizeConstraints] + 36
10 UIKit 0x024b0480 -[UIView(UIConstraintBasedLayout) _updateContentSizeConstraints] + 511
11 UIKit 0x024b67bf -[UIView(AdditionalLayoutSupport) updateConstraints] + 110
12 UIKit 0x01fd6579 -[UILabel updateConstraints] + 189
13 UIKit 0x024b6058 -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 239
14 UIKit 0x024b61d6 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 122
15 UIKit 0x024b6157 __UIViewRecursionHelper + 40
16 CoreFoundation 0x00b0bc69 CFArrayApplyFunction + 57
17 UIKit 0x024b5ffc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 147
18 UIKit 0x024b61d6 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 122
19 UIKit 0x024b6157 __UIViewRecursionHelper + 40
20 CoreFoundation 0x00b0bc69 CFArrayApplyFunction + 57
21 UIKit 0x024b5ffc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 147
22 UIKit 0x024b61d6 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 122
23 UIKit 0x024b6157 __UIViewRecursionHelper + 40
24 CoreFoundation 0x00b0bc69 CFArrayApplyFunction + 57
25 UIKit 0x024b5ffc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 147
26 UIKit 0x024b61d6 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 122
27 UIKit 0x024b6157 __UIViewRecursionHelper + 40
28 CoreFoundation 0x00b0bc69 CFArrayApplyFunction + 57
29 UIKit 0x024b5ffc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 147
30 UIKit 0x024b61d6 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 122
31 UIKit 0x024b6157 __UIViewRecursionHelper + 40
32 CoreFoundation 0x00b0bc69 CFArrayApplyFunction + 57
33 UIKit 0x024b5ffc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 147
34 UIKit 0x024b61d6 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 122
35 UIKit 0x024b6157 __UIViewRecursionHelper + 40
36 CoreFoundation 0x00b0bc69 CFArrayApplyFunction + 57
37 UIKit 0x024b5ffc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 147
38 UIKit 0x024b61d6 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 122
39 UIKit 0x024b6157 __UIViewRecursionHelper + 40
40 CoreFoundation 0x00b0bc69 CFArrayApplyFunction + 57
41 UIKit 0x024b5ffc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 147
42 UIKit 0x024b61d6 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 122
43 UIKit 0x024b6157 __UIViewRecursionHelper + 40
44 CoreFoundation 0x00b0bc69 CFArrayApplyFunction + 57
45 UIKit 0x024b5ffc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 147
46 UIKit 0x024b61d6 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 122
47 UIKit 0x024b6157 __UIViewRecursionHelper + 40
48 CoreFoundation 0x00b0bc69 CFArrayApplyFunction + 57
49 UIKit 0x024b5ffc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 147
50 UIKit 0x024b61d6 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 122
51 UIKit 0x024b6157 __UIViewRecursionHelper + 40
52 CoreFoundation 0x00b0bc69 CFArrayApplyFunction + 57
53 UIKit 0x024b5ffc -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 147
54 UIKit 0x024b61d6 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPass:] + 122
55 UIKit 0x024aa878 __62-[UIWindow(UIConstraintBasedLayout) updateConstraintsIfNeeded]_block_invoke + 43
56 Foundation 0x02f0b68c -[NSISEngine withBehaviors:performModifications:] + 107
57 Foundation 0x02d9b3c5 -[NSISEngine withAutomaticOptimizationDisabled:] + 48
58 UIKit 0x024aa590 -[UIWindow(UIConstraintBasedLayout) updateConstraintsIfNeeded] + 225
59 UIKit 0x024aa467 -[UIWindow(UIConstraintBasedLayout) layoutSublayersOfLayer:] + 90
60 libobjc.A.dylib 0x0316a82b -[NSObject performSelector:withObject:] + 70
61 QuartzCore 0x0171a45a -[CALayer layoutSublayers] + 148
62 QuartzCore 0x0170e244 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 380
63 QuartzCore 0x0170e0b0 _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 26
64 QuartzCore 0x016747fa _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 294
65 QuartzCore 0x01675b85 _ZN2CA11Transaction6commitEv + 393
66 QuartzCore 0x01676258 _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 92
67 CoreFoundation 0x00b3236e __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 30
68 CoreFoundation 0x00b322bf __CFRunLoopDoObservers + 399
69 CoreFoundation 0x00b10254 __CFRunLoopRun + 1076
70 CoreFoundation 0x00b0f9d3 CFRunLoopRunSpecific + 467
71 CoreFoundation 0x00b0f7eb CFRunLoopRunInMode + 123
72 GraphicsServices 0x041945ee GSEventRunModal + 192
73 GraphicsServices 0x0419442b GSEventRun + 104
74 UIKit 0x01e18f9b UIApplicationMain + 1225
75 RestAppXXI 0x000305ed main + 141
76 libdyld.dylib 0x049eb6d9 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)

Answer 1

That is not relevant to your UITableView. That is most probably from a string you are trying to access, but it's nil.

Answer 2

User exception break point to debug, you are calling length method on NSNull object
And why to use NSTimer, you can reload table after getting response from server