iOS crash report: EXC_CRASH (SIGABRT) - stringByAppendingString - ios

Question

I am trying to fix a bug that I am not able to recreate, it doesn't happen to my device (iPhone 5s) or in any iOS simulator but happened only once in an iPhone 7 of my client. When the client deleted and downloaded again the app, the bug disappeared, so I am searching for a ghost now.
I was able to get the crash log file from the clients phone and symbolicate it. Here are some useful informations I extracted:
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Exception Note: EXC_CORPSE_NOTIFY
Triggered by Thread: 0
In the un-symbolicated crash report: (check 2 and 3 line)
Last Exception Backtrace:
0 CoreFoundation 0x18c92efe0 __exceptionPreprocess + 124
1 libobjc.A.dylib 0x18b390538 objc_exception_throw + 56
2 CoreFoundation 0x18c92ef28 +[NSException raise:format:] + 116
3 Foundation 0x18d324df0 -[NSString stringByAppendingString:] + 112
4 myApp 0x100119ea8 0x100004000 + 1138344
5 myApp 0x100119784 0x100004000 + 1136516
6 UIKit 0x192ad1204 -[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:] + 380
7 UIKit 0x192cdd738 -[UIApplication _callInitializationDelegatesForMainScene:transitionContext:] + 3452
8 UIKit 0x192ce31e0 -[UIApplication _runWithMainScene:transitionContext:completion:] + 1684
9 UIKit 0x192cf7d18 __84-[UIApplication _handleApplicationActivationWithScene:transitionContext:completion:]_block_invoke.3151 + 48
10 UIKit 0x192ce0474 -[UIApplication workspaceDidEndTransaction:] + 168
11 FrontBoardServices 0x18e4d7884 __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 36
12 FrontBoardServices 0x18e4d76f0 -[FBSSerialQueue _performNext] + 176
13 FrontBoardServices 0x18e4d7aa0 -[FBSSerialQueue _performNextFromRunLoopSource] + 56
14 CoreFoundation 0x18c8dd42c __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 24
15 CoreFoundation 0x18c8dcd9c __CFRunLoopDoSources0 + 540
16 CoreFoundation 0x18c8da9a8 __CFRunLoopRun + 744
17 CoreFoundation 0x18c80ada4 CFRunLoopRunSpecific + 424
18 UIKit 0x192aca384 -[UIApplication _run] + 652
19 UIKit 0x192ac5058 UIApplicationMain + 208
20 myApp 0x10014b8ac 0x100004000 + 1341612
21 libdyld.dylib 0x18b81959c start + 4
and in the symbolicated crash report:(check 4 and 5 line)
Last Exception Backtrace:
0 CoreFoundation 0x185f7fd38 0x185e3e000 + 1318200
1 libobjc.A.dylib 0x185494528 0x18548c000 + 34088
2 CoreFoundation 0x185f7fc80 0x185e3e000 + 1318016
3 Foundation 0x18686e760 0x186862000 + 51040
4 myApp 0x10469f928 -[AppDelegate initViewController] (AppDelegate.m:96)
5 myApp 0x10469f520 -[AppDelegate application:didFinishLaunchingWithOptions:] (AppDelegate.m:30)
6 UIKit 0x18f3ff050 0x18f380000 + 520272
7 UIKit 0x18f5f2898 0x18f380000 + 2566296
8 UIKit 0x18f5f76e4 0x18f380000 + 2586340
9 UIKit 0x18f885454 0x18f380000 + 5264468
10 UIKit 0x18fb551f0 0x18f380000 + 8212976
11 UIKit 0x18f8850b8 0x18f380000 + 5263544
12 UIKit 0x18f885928 0x18f380000 + 5265704
13 UIKit 0x18ffee6e8 0x18f380000 + 13035240
14 UIKit 0x18ffee58c 0x18f380000 + 13034892
15 UIKit 0x18fd6a9c0 0x18f380000 + 10398144
16 UIKit 0x18fefffc8 0x18f380000 + 12058568
17 UIKit 0x18fd6a870 0x18f380000 + 10397808
18 UIKit 0x18fb54850 0x18f380000 + 8210512
19 UIKit 0x18f5f5e28 0x18f380000 + 2580008
20 UIKit 0x18f9f96ec 0x18f380000 + 6788844
21 FrontBoardServices 0x188621768 0x188615000 + 51048
22 FrontBoardServices 0x18862a070 0x188615000 + 86128
23 libdispatch.dylib 0x185905048 0x185904000 + 4168
24 libdispatch.dylib 0x18590c6c8 0x185904000 + 34504
25 FrontBoardServices 0x188655a04 0x188615000 + 264708
26 FrontBoardServices 0x1886556a8 0x188615000 + 263848
27 FrontBoardServices 0x188655c44 0x188615000 + 265284
28 CoreFoundation 0x185f28358 0x185e3e000 + 959320
29 CoreFoundation 0x185f282d8 0x185e3e000 + 959192
30 CoreFoundation 0x185f27b60 0x185e3e000 + 957280
31 CoreFoundation 0x185f25738 0x185e3e000 + 948024
32 CoreFoundation 0x185e462d8 0x185e3e000 + 33496
33 GraphicsServices 0x187cd7f84 0x187ccd000 + 44932
34 UIKit 0x18f3f3880 0x18f380000 + 473216
35 myApp 0x1046bc124 main (main.m:14)
36 libdyld.dylib 0x18596a56c 0x185969000 + 5484
So at the third line of the un-symbolicated crash report it says:
0x18d324df0 -[NSString stringByAppendingString:] + 112
and at the 4th line of the symbolicated crash report:
0x10469f928 -[AppDelegate initViewController] (AppDelegate.m:96)
In my AppDelegate at the 96 line I have this code:
NSString *backColorString = [#"#" stringByAppendingString:[myModel sharedInstance].theme.BackColor];
So the only thing that can be wrong with this, if the problem is indeed here(?) is that the
[HotelStay sharedInstance].theme.BackColor
must return nil or "".
The thing is that I tried both and I couldn't be able to recreate the problem. Is there something I am missing or doing wrong here?

Answer 1

if you use stringByAppendingString on an NSString than you end up with leaks because the pointer associated with the initial NSString moves around, pointing to the new string created by the append, whereas with NSMutableString, your pointer always points to that mutable string. I guess it should be the issue but what I am thinking is according to Apple Documentation The string to append to the receiver. This value must not be nil if its nil it will Raise a NSInvalidArgumentException.