Fade Transition for Android (Kotlin)

FadeTransition.kt

class FadeTransition : Transition {
    companion object {
        private const val PROPNAME_ALPHA = "android:fadeTransition:alpha"
        private val TRANSITION_PROPERTIES = arrayOf(PROPNAME_ALPHA)
    }

    constructor(context: Context, attrs: AttributeSet) : super(context, attrs) {}
    constructor() : super()

    private fun captureValues(transitionValues: TransitionValues) {
        transitionValues.values[PROPNAME_ALPHA] = transitionValues.view.alpha
    }

    override fun captureStartValues(transitionValues: TransitionValues) = captureValues(transitionValues)
    override fun captureEndValues(transitionValues: TransitionValues) = captureValues(transitionValues)
    override fun getTransitionProperties() = TRANSITION_PROPERTIES

    override fun createAnimator(
        sceneRoot: ViewGroup,
        startValues: TransitionValues?,
        endValues: TransitionValues?
    ): Animator? {
        if (startValues == null || endValues == null) {
            return null
        }
        val startAlpha: Float = startValues.values[PROPNAME_ALPHA] as? Float ?: 1F
        val endAlpha: Float = endValues.values[PROPNAME_ALPHA] as? Float ?: 1F

        return ObjectAnimator.ofFloat(endValues.view, View.ALPHA, startAlpha, endAlpha)
    }
}

move_fade.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- New transition resource file, using FadeTransition, as well as defaults from android.R.transition.move -->
<transitionSet xmlns:android="http://schemas.android.com/apk/res/android">
    <changeBounds/>
    <changeTransform/>
    <changeClipBounds/>
    <changeImageTransform/>
    <transition class="full.qualified.name.of.FadeTransition" />
</transitionSet>