Crash in ios app

Question

I included crashlytics in my ios app and distributed it via enterprise. Crashlytics keeps on reporting below crash daily regarding Reachability. I googled, but didn't get what causing this crash.

    Fatal Exception: NSInvalidArgumentException
-[__NSMallocBlock__ reachabilityChanged:]: unrecognized selector sent to instance 0x1c5cdfc0


Thread : Fatal Exception: NSInvalidArgumentException
0  CoreFoundation                 0x316642a3 __exceptionPreprocess + 162
1  libobjc.A.dylib                0x3252297f objc_exception_throw + 30
2  CoreFoundation                 0x31667e07 -[NSObject(NSObject) doesNotRecognizeSelector:] + 170
3  CoreFoundation                 0x31666531 ___forwarding___ + 392
4  CoreFoundation                 0x315bdf68 _CF_forwarding_prep_0 + 24
5  CoreFoundation                 0x315b5037 _CFXNotificationPost + 1426
6  Foundation                     0x3319ed91 -[NSNotificationCenter postNotificationName:object:userInfo:] + 72
7  Foundation                     0x331a2853 -[NSNotificationCenter postNotificationName:object:] + 30
8                                 0x0005aee9 ReachabilityCallback (Reachability.m:94)
9  SystemConfiguration            0x30f5f161 reachPerform + 924
10 CoreFoundation                 0x31639683 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 14
11 CoreFoundation                 0x31638ee9 __CFRunLoopDoSources0 + 212
12 CoreFoundation                 0x31637cb7 __CFRunLoopRun + 646
13 CoreFoundation                 0x315aaebd CFRunLoopRunSpecific + 356
14 CoreFoundation                 0x315aad49 CFRunLoopRunInMode + 104
15 GraphicsServices               0x393a82eb GSEventRunModal + 74
16 UIKit                          0x38e662f9 UIApplicationMain + 1120
17                           0x00076f2f main (main.m:16)
18 libdyld.dylib                  0x350bab20 start

Answer 1

It looks like you're registering a reachability observer which is being deallocated but not removing itself as an observer before that happens. So, when the reachability notification is posted later it is sent to a deallocated instance (i.e. random memory location) and you get a crash.

All observers (whether of reachability or any other notification with NSNotificationCenter) should remove themselves as an observer before they are deallocated.