Understanding Firebase Crashlytics report for iOS app - ios

Question

I have an iOS app that uses Firebase Crashlytics for reporting crashes. Now I have a report for a crash but my problem is that I could not understand what exactly caused the crash from this report.
Crashlytics report:
Crashed: com.apple.main-thread
0 Nail it 0x104db77a8 CaseDetailsViewController.getbaseData() + 253
(CaseDetailsViewController.swift:253)
1 Nail it 0x104db5168 CaseDetailsViewController.viewDidLoad() + 4335047016 (<compiler-generated>:4335047016)
2 Nail it 0x104db521c #objc CaseDetailsViewController.viewDidLoad() + 4335047196 (<compiler-generated>:4335047196)
3 UIKitCore 0x185d11658 -[UIViewController _sendViewDidLoadWithAppearanceProxyObjectTaggingEnabled] + 100
4 UIKitCore 0x185d160e8 -[UIViewController loadViewIfRequired] + 936
5 UIKitCore 0x185d164f0 -[UIViewController view] + 28
6 UIKit 0x1b913374c -[UIViewControllerAccessibility dismissViewControllerWithTransition:completion:] + 268
7 UIKitCore 0x185d28d6c -[UIViewController _performCoordinatedPresentOrDismiss:animated:] + 508
8 UIKitCore 0x185d2b474 -[UIViewController dismissViewControllerAnimated:completion:] + 132
9 UIKit 0x1b91333c0 -[UIViewControllerAccessibility dismissViewControllerAnimated:completion:] + 120
10 Nail it 0x104db98ec #objc CaseDetailsViewController.backButton(_:) + 4335065324 (<compiler-generated>:4335065324)
11 UIKitCore 0x18635a72c -[UIApplication sendAction:to:from:forEvent:] + 96
12 UIKitCore 0x185a05474 __45-[_UIButtonBarTargetAction _invoke:forEvent:]_block_invoke + 80
13 UIKitCore 0x185a05304 -[_UIButtonBarTargetAction _invoke:forEvent:] + 236
14 UIKitCore 0x18635a72c -[UIApplication sendAction:to:from:forEvent:] + 96
15 UIKitCore 0x185d6aed0 -[UIControl sendAction:to:forEvent:] + 240
16 UIKitCore 0x185d6b228 -[UIControl _sendActionsForEvents:withEvent:] + 396
17 UIKitCore 0x185d6a24c -[UIControl touchesEnded:withEvent:] + 516
18 UIKitCore 0x18639449c -[UIWindow _sendTouchesForEvent:] + 1280
19 UIKitCore 0x186395c64 -[UIWindow sendEvent:] + 3468
20 UIKitCore 0x1863718ec -[UIApplication sendEvent:] + 344
21 UIKit 0x1b90db80c -[UIApplicationAccessibility sendEvent:] + 96
22 UIKitCore 0x1863f2970 __dispatchPreprocessedEventFromEventQueue + 6808
23 UIKitCore 0x1863f54ec __handleEventQueueInternal + 5364
24 UIKitCore 0x1863ed168 __handleHIDEventFetcherDrain + 140
25 CoreFoundation 0x182223ad8 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 24
26 CoreFoundation 0x182223a30 __CFRunLoopDoSource0 + 80
27 CoreFoundation 0x1822231b8 __CFRunLoopDoSources0 + 184
28 CoreFoundation 0x18221e1e8 __CFRunLoopRun + 788
29 CoreFoundation 0x18221dba8 CFRunLoopRunSpecific + 424
30 GraphicsServices 0x18c394344 GSEventRunModal + 160
31 UIKitCore 0x1863593e4 UIApplicationMain + 1932
32 Nail it 0x104d797cc main + 16 (AppDelegate.swift:16)
33 libdyld.dylib 0x1820a58f0 start + 4
Below is the function getBaseData() from CasesDetails View Controller:
func getbaseData(){
let userDefaults = UserDefaults.standard
mobile = userDefaults.value(forKey: "mobile") as! String
altenativeMobile = userDefaults.string(forKey: "altenativeMobile") ?? mobile
privateKey = userDefaults.value(forKey: "privateKey") as! String
////reading JSON
let categoriesJsonString = userDefaults.value(forKey: "categoriesString") as! String
let data = categoriesJsonString.data(using: .utf8)!
if let json = try? JSON(data: data) {
let arrayCats = json["content"][1]["caseMappings"][caseCategoryGlobal].array
if(isNoSubsGlob == 0){
if let arrayCatsCount = arrayCats?.count {
print("The array has been created with \(arrayCatsCount) element")
print("sub1Glob= \(sub1Glob) & sub2Glob= \(sub2Glob)")
for var i in 0..<arrayCatsCount{
let sub1 = json["content"][1]["caseMappings"][caseCategoryGlobal][i]["sub1"].string!
let sub2 = json["content"][1]["caseMappings"][caseCategoryGlobal][i]["sub2"].string ?? ""
if (sub1 == sub1Glob && sub2 == sub2Glob){
departmentId = json["content"][1]["caseMappings"][caseCategoryGlobal][i]["departmentId"].int!
WorkTypeId = json["content"][1]["caseMappings"][caseCategoryGlobal][i]["categoryId"].int!
issueCode = json["content"][1]["caseMappings"][caseCategoryGlobal][i]["id"].int!
}
}
}
}else{
departmentId = json["content"][1]["caseMappings"][caseCategoryGlobal][0]["departmentId"].int!
WorkTypeId = json["content"][1]["caseMappings"][caseCategoryGlobal][0]["categoryId"].int!
issueCode = json["content"][1]["caseMappings"][caseCategoryGlobal][0]["id"].int!
}
}
contactNumberText.text = altenativeMobile
}
and the line 235 is (contactNumberText.text = altenativeMobile) as the last line in the code above

Answer 1

All UI stuff should be performed on main thread, that is what your crash report shows (crash due to main thread.)
So your last line should be :
DispatchQueue.main.async {
self.contactNumberText.text = altenativeMobile
}
Update this line, your crash will fixed.