https://t.me/drakeets/390

QuickReturnDelegate.kt

import android.support.v7.widget.RecyclerView

/**
 * @author drakeet
 */
class QuickReturnDelegate(private val scrollSlop: Int = 12) : RecyclerView.OnScrollListener() {

  private lateinit var callback: (hide: Boolean) -> Unit

  private var scrollY: Int = 0


  fun attach(recyclerView: RecyclerView, callback: (hide: Boolean) -> Unit) {
    this.callback = callback
    recyclerView.addOnScrollListener(this)
  }


  override fun onScrollStateChanged(recyclerView: RecyclerView?, newState: Int) {
    if (newState == RecyclerView.SCROLL_STATE_IDLE) {
      scrollY = 0
    }
  }


  override fun onScrolled(recyclerView: RecyclerView?, dx: Int, dy: Int) {
    scrollY += dy
    callback(scrollY > scrollSlop)
  }
}