IssueTracker

Component used: livecycle-livedata-ktx Version used: 2.5.1

Issue 214434197 was reported for distinctUntilChanged() which does not set the initial value of the returned LiveData even if the source one was initialized. This caused unnecessary recompositions if observed with observeAsState().

However, I also noticed that the other two Transformations methods, map and switchMap, suffer from the same symptom which means that they too will likely cause the same unnecessary recompositions.

    @Test
    fun `map() should return livedata with trasformed initial value of source`() {
        // given
        val initialValue = "barboutsala"
        val source = MutableLiveData(initialValue)

        // when
        val mapped = source.map { it }

        // then
        assertEquals(initialValue, source.value)
        assertEquals(initialValue, mapped.value) // <-- this fails
    }

    @Test
    fun `switchMap() should return livedata with same initial value as source`() {
        // given
        val initialValue1 = "barboutsala 1"
        val initialValue2 = "barboutsala 2"
        val original = MutableLiveData(true)
        val source1 = MutableLiveData(initialValue1)
        val source2 = MutableLiveData(initialValue2)

        // when
        val switched = original.switchMap { if (it) source1 else source2 }

        // then
        assertEquals(initialValue1, source1.value)
        assertEquals(initialValue1, switched.value) // <-- this fails

        original.value = false
        assertEquals(initialValue2, source2.value)
        assertEquals(initialValue2, switched.value) // <-- this also fails!
    }