Be aware of the Date and Time Format in Android.

This blog is about a bug that can crash your app that you may not even consider.

I was developing an application. Everything was working as expected, and I was happy until I made some test releases and encountered crashes in some testing devices.

Hopefully, I already integrated firebase crashlytics. Guess what, the bug was happening in the date parsing section of the code:

fun parseDate(date: Long): String {
    val format = DateFormat.getDateTimeInstance()
    format.timeZone = TimeZone.getDefault()
    return format.format(date * 1000).toString()
}

Ps: date comes from an API, and its format is in the epoch format.

Nothing odd happened until I used this to show users a portion of the date.

Text(
  text = parseDate(someData.aDateTimeValue).getDate()
)

fun String.getDate(): String {
    return this.split(" ").subList(0,3).joinToString(" ")
}

Did you guess the problem?

Let me explain:

The real problem is that some people prefer a 12-hour time format, and some others a 24-hour format on their devices. And by using getDateTimeInstance(), you are converting to the device format. This is what the java doc says:

Gets the date/time formatter with the default formatting style for the default FORMAT locale.

And when you take a sublist of the wrong formatted string, you sometimes encounter the IndexOutOfBoundsException.

How to fix this?

Instead of using DateFormat, use SimpleDateFormat and mention the format to which you want to cast the date. For instance, I changed the parseDate function to the following:

fun parseDate(date: Long): String {
    val format = SimpleDateFormat("MMM dd, YYYY hh:mm:ss a")
    format.timeZone = TimeZone.getDefault()
    return format.format(date * 1000).toString()
}

⚠️ Note: This is a critical bug you may cause in production that causes App Crash. Also, It has a test scenario that one may not consider.

Best of luck with your bug tracking.