Observable stream of AppBarLayout offsets + scroll direction from https://twitter.com/pandanomic/status/898142281106022400

OffsetsWithDirection.kt

/*
 * Here we want to get the appbar offset changes paired with the direction it's moving and
 * using RxBinding's great `offsetChanges` API to make an rx Observable of this. The first
 * part buffers two while skipping one at a time and emits y delta pairs (cur and prev). Second 
 * part is just a simple map to pair the offset with the resolved scroll direction comparing 
 * to the previous offset. This gives us a nice stream of (offset, direction) emissions.
 *
 * Note that the filter() is important if you manipulate child views of the ABL. If any child
 * view requests layout again, it will trigger an emission from the offset listener with the
 * same value as before, potentially causing measure/layout/draw thrashing if your logic 
 * reacting to the offset changes *is* manipulating those child views (vicious cycle).
 */
RxAppBarLayout.offsetChanges(appBarLayout)
    .buffer(2, 1) // Buffer in pairs to compare the previous, skip 1 at a time
    .filter { it[1] != it[0] }
    .map { Pair(it[1], ScrollDirection.resolve(it[1], it[0])) }  // Map to a direction
    .subscribe { (offset, direction) ->
      // Profit
    }

ScrollDirection.kt

enum class ScrollDirection {
  UP, DOWN;

  companion object {
    fun resolve(current: Int, prev: Int): ScrollDirection {
      return if (current > prev) {
        DOWN
      } else {
        UP
      }
    }
  }
}