Understand a crashlog from Fabrics

Question

I have integrated crashlytics into my iOS app. And I got a crash log like this

# Issue #: 1
# Issue ID: 59940bb4be077a4dcc2837ff
# Session ID: 
e68dd53b640d4ac39f21b511a9f78b78_90910b25826211e7a25d56847afe9799_0_v2
# Date: 2017-08-16T06:30:00Z
# OS Version: 10.3.3 (14G60)
# Device: iPhone 6s
# RAM Free: 3.8%
# Disk Free: 15.2%

#0. Crashed: com.apple.main-thread
0  MY APP                         0x100086b50 specialized static Functions.retunDateStringFromDateString(dateString : String, inuputFormat : String, outPutFormat : String) -> String (Functions.swift:123)
1  MY APP                         0x1000ef820 specialized TeamAttendanceViewController.tableView(UITableView, cellForRowAt : IndexPath) -> UITableViewCell (Functions.swift)
2  MY APP                         0x1000eaa78 @objc TeamAttendanceViewController.tableView(UITableView, cellForRowAt : IndexPath) -> UITableViewCell (TeamAttendanceViewController.swift)
3  UIKit                          0x193641d90 -[UITableView _createPreparedCellForGlobalRow:withIndexPath:willDisplay:] + 688
4  UIKit                          0x193641fa8 -[UITableView _createPreparedCellForGlobalRow:willDisplay:] + 80
5  UIKit                          0x19362f6ac -[UITableView _updateVisibleCellsNow:isRecursive:] + 2152
6  UIKit                          0x193646f98 -[UITableView _performWithCachedTraitCollection:] + 120
7  UIKit                          0x1933df49c -[UITableView layoutSubviews] + 176
8  UIKit                          0x1932f9cc0 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1200
9  QuartzCore                     0x1904ea274 -[CALayer layoutSublayers] + 148
10 QuartzCore                     0x1904dede8 
CA::Layer::layout_if_needed(CA::Transaction*) + 292
11 QuartzCore                     0x1904deca8 
CA::Layer::layout_and_display_if_needed(CA::Transaction*) + 32
12 QuartzCore                     0x19045a34c 
CA::Context::commit_transaction(CA::Transaction*) + 252
13 QuartzCore                     0x1904813ac 
CA::Transaction::commit() + 504
14 QuartzCore                     0x190481e78 
CA::Transaction::observer_callback(__CFRunLoopObserver*, unsigned 
long, void*) + 120
15 CoreFoundation                 0x18d1789a8 
__CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 32
16 CoreFoundation                 0x18d176630 __CFRunLoopDoObservers 
+ 372
17 CoreFoundation                 0x18d176a7c __CFRunLoopRun + 956
18 CoreFoundation                 0x18d0a6da4 CFRunLoopRunSpecific + 
424
19 GraphicsServices               0x18eb11074 GSEventRunModal + 100
20 UIKit                          0x193361c9c UIApplicationMain + 208
21 MY APP                         0x10002f710 main 
(AppDelegate.swift:16)
22 libdyld.dylib                  0x18c0b559c start + 4

this is the first time I'm going to read a crash log file. As I understand. There is something wrong with my Functionclass's returnDateString method's 123 line. But how can I understand what is the exact issue in this line? And this is my method in the Function class.

class func retunDateStringFromDateString(dateString : String,inuputFormat: String, outPutFormat : String) -> String{
    if(dateString != ""){
        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = inuputFormat//this your string date format

        let date = dateFormatter.date(from: dateString)


        dateFormatter.dateFormat = outPutFormat///this is what you want to convert format

        let timeStamp = dateFormatter.string(from: date!)


        return timeStamp
    }else{
        return ""
    }

}

And this is my 123 line. let timeStamp = dateFormatter.string(from: date!)

What would be the reason for this? Please help me. Thanks

UPDATE

var inTimeArray = inTime?.components(separatedBy: ".")
print(inTimeArray)

cell.inOneTime.text = Functions.nullToNilForString(value: Functions.retunDateStringFromDateString(dateString: (inTimeArray?[0])! ,inuputFormat: "yyyy-MM-dd'T'HH:mm:ss", outPutFormat:  "HH:mm") as AnyObject?)?.description

Answer 1

Based on the discussion in comments, it seems that the locale settings are different on your user's device than on your test devices and different locales can cause trouble when using explicit date formats.

As I have already stated in comments, do not force unwrap the date value, rather use optional unwrapping and show an error message to the user if dateFormatter.date(from: String) fails.

You should either change your dateFormat to a format that is locale independent, or set dateFormatter.locale = Locale(identifier: "en_US_POSIX") or any other locale that you have tested your explicit date formats with.

As for understanding the crashlog, crash logs only show a stack trace, they cannot tell you the exact cause of the trouble, since in release mode your app is not running in debugger and hence there can be no breakpoints to catch and identify a runtime exception. However, as you did here, you can pinpoint the error to the line causing it in most cases.

Answer 2

The most likely problem here is that you are force unwrapping your optional date parameter. If it can't parse dateString into a date in the first place, date will be nil and force unwrapping will cause a crash.

Try something like this instead:

guard let date = dateFormatter.date(from: dateString) else {
    // handle the error
    return ""
}
//...
return dateFormatter.string(from: date)

See the docs on optionals to get a better understanding https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/TheBasics.html