How to check for nil on a Realm Results array value - ios

Question

I'm trying to figure out why I cannot check for nil on the following function call:
var allExercises : Results<Exercises>?
var exerciseIndex : Int = 0
#objc func goToNextExercise(){
if allExercises?[exerciseIndex] != nil {
print("Does not equal nil")
exerciseIndex += 1
} else {
print("Does equal nil")
}
}
When allExercises?[exerciseIndex] does equal nil, the application crashes and I get an "indexPath out of Range" error:
*** Terminating app due to uncaught exception 'RLMException', reason: 'Index 3 is out of bounds (must be less than 3).'
*** First throw call stack:
(
0 CoreFoundation 0x0000000104a7127e __exceptionPreprocess + 350
1 libobjc.A.dylib 0x00000001048deb20 objc_exception_throw + 48
2 SectionRowsTutorial 0x00000001025d7aae _Z20RLMThrowResultsErrorP8NSString + 670
3 SectionRowsTutorial 0x00000001025d8cc6 _ZL25translateRLMResultsErrorsIZ28-[RLMResults objectAtIndex:]E3$_6EDaOT_P8NSString + 118
4 SectionRowsTutorial 0x00000001025d8bf4 -[RLMResults objectAtIndex:] + 100
5 SectionRowsTutorial 0x000000010278c9dc $s10RealmSwift7ResultsVyxSicig + 236
6 SectionRowsTutorial 0x00000001022dc576 $s19SectionRowsTutorial19ThirdViewControllerC16goToNextExerciseyyF + 246
7 SectionRowsTutorial 0x00000001022dc87b $s19SectionRowsTutorial19ThirdViewControllerC16goToNextExerciseyyFTo + 43
8 UIKitCore 0x0000000108571fff -[UIApplication sendAction:to:from:forEvent:] + 83
9 UIKitCore 0x0000000107f4a00e -[UIControl sendAction:to:forEvent:] + 223
10 UIKitCore 0x0000000107f4a358 -[UIControl _sendActionsForEvents:withEvent:] + 398
11 UIKitCore 0x0000000107f492b7 -[UIControl touchesEnded:withEvent:] + 481
12 UIKitCore 0x00000001085acbbf -[UIWindow _sendTouchesForEvent:] + 2604
13 UIKitCore 0x00000001085ae4c6 -[UIWindow sendEvent:] + 4596
14 UIKitCore 0x000000010858953b -[UIApplication sendEvent:] + 356
15 UIKitCore 0x000000010860a71a __dispatchPreprocessedEventFromEventQueue + 6847
16 UIKitCore 0x000000010860d1e0 __handleEventQueueInternal + 5980
17 CoreFoundation 0x00000001049d4471 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
18 CoreFoundation 0x00000001049d439c __CFRunLoopDoSource0 + 76
19 CoreFoundation 0x00000001049d3b74 __CFRunLoopDoSources0 + 180
20 CoreFoundation 0x00000001049ce87f __CFRunLoopRun + 1263
21 CoreFoundation 0x00000001049ce066 CFRunLoopRunSpecific + 438
22 GraphicsServices 0x000000010e756bb0 GSEventRunModal + 65
23 UIKitCore 0x0000000108570d4d UIApplicationMain + 1621
24 SectionRowsTutorial 0x00000001022e759b main + 75
25 libdyld.dylib 0x0000000105ba4c25 start + 1
26 ??? 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

Answer 1

You are checking the value of allExercises, if you pass a greater index than the array size, it's crashing. for check, you should first check if exerciseIndex is less than allExercises count - 1 and then check data
if exerciseIndex <= allExercises.count - 1