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kotlinlong-integernullablemutablelivedata

Why is my MutableLiveData<Long> nullable?

I would like to know why my elapsed variable ends up Long? instead of Long. I defined it as not nullable and none of the operations I execute on it could result in null.

Still get the error for the last line:

Operator call corresponds to a dot-qualified call 'elapsed.div(1000.toLong())' which is not allowed on a nullable receiver 'elapsed'.

var startTime: Long = 0
var _elapsedTime = MutableLiveData<Long>(0)
_elapsedTime.value = System.currentTimeMillis() - startTime
val elapsed = _elapsedTime.value
val testVal = elapsed / 1000.toLong()
Solution

  • It ends up as Long? because the method LiveData.getValue() is marked with @Nullable in Java.

    For the interoperability between Java and Kotlin, in Kotlin that method returns a nullable Long, so Long?.

    https://kotlinlang.org/docs/reference/java-interop.html#nullability-annotations