getValueAnimator.kt

inline fun getValueAnimator(forward: Boolean = true, duration: Long, interpolator: TimeInterpolator,
                            crossinline updateListener: (progress: Float) -> Unit
): ValueAnimator {
    val a =
            if (forward) ValueAnimator.ofFloat(0f, 1f)
            else ValueAnimator.ofFloat(1f, 0f)
    a.addUpdateListener { updateListener(it.animatedValue as Float) }
    a.duration = duration
    a.interpolator = interpolator
    return a
}