HideBottomViewOnScrollBehavior that ensures BottomView visibility

HideBottomViewOnScrollBehavior.kt

import android.animation.Animator
import android.animation.AnimatorListenerAdapter
import android.animation.TimeInterpolator
import android.content.Context
import android.support.design.animation.AnimationUtils
import android.support.design.widget.CoordinatorLayout
import android.support.design.widget.Snackbar
import android.support.v4.view.ViewCompat
import android.support.v7.widget.RecyclerView
import android.util.AttributeSet
import android.view.Gravity
import android.view.View
import android.view.ViewPropertyAnimator
import android.view.ViewTreeObserver.OnGlobalLayoutListener

/**
 * @see <a href="https://github.com/material-components/material-components-android/blob/master/lib/java/com/google/android/material/behavior/HideBottomViewOnScrollBehavior.java">HideBottomViewOnScrollBehavior.java</a>
 */
class HideBottomViewOnScrollBehavior<V : View>(context: Context, attrs: AttributeSet) :
        CoordinatorLayout.Behavior<V>(context, attrs) {

    private var height: Int = 0
    private var currentState = STATE_SCROLLED_UP
    private var currentAnimator: ViewPropertyAnimator? = null

    override fun layoutDependsOn(parent: CoordinatorLayout, child: V, dependency: View): Boolean {
        if (dependency is Snackbar.SnackbarLayout) {
            updateSnackbar(child, dependency)
        }
        return super.layoutDependsOn(parent, child, dependency)
    }

    private fun updateSnackbar(child: View, snackbarLayout: Snackbar.SnackbarLayout) {
        val params = snackbarLayout.layoutParams as? CoordinatorLayout.LayoutParams
        params?.run {
            anchorId = child.id
            anchorGravity = Gravity.TOP
            gravity = Gravity.TOP
            snackbarLayout.layoutParams = params
        }
    }

    override fun onStopNestedScroll(coordinatorLayout: CoordinatorLayout, child: V, target: View, type: Int) {
        super.onStopNestedScroll(coordinatorLayout, child, target, type)
        assureBottomViewVisibility(target, child)
    }

    override fun onLayoutChild(parent: CoordinatorLayout, child: V, layoutDirection: Int): Boolean {
        height = child.measuredHeight
        return super.onLayoutChild(parent, child, layoutDirection)
    }

    override fun onStartNestedScroll(coordinatorLayout: CoordinatorLayout, child: V, directTargetChild: View,
                                     target: View, axes: Int, type: Int): Boolean =
            axes == ViewCompat.SCROLL_AXIS_VERTICAL

    override fun onNestedScroll(coordinatorLayout: CoordinatorLayout, child: V,
                                target: View, dxConsumed: Int, dyConsumed: Int, dxUnconsumed: Int, dyUnconsumed: Int,
                                @ViewCompat.NestedScrollType type: Int) {
        if (currentState != STATE_SCROLLED_DOWN && dyConsumed > 0) {
            slideDown(child)
        } else if (currentState != STATE_SCROLLED_UP && dyConsumed < 0) {
            slideUp(child)
        }
    }

    private fun slideUp(child: V) {
        if (currentAnimator != null) {
            currentAnimator?.cancel()
            child.clearAnimation()
        }
        currentState = STATE_SCROLLED_UP
        animateChildTo(child, 0, ENTER_ANIMATION_DURATION, AnimationUtils.LINEAR_OUT_SLOW_IN_INTERPOLATOR)
    }

    private fun slideDown(child: V) {
        if (currentAnimator != null) {
            currentAnimator?.cancel()
            child.clearAnimation()
        }
        currentState = STATE_SCROLLED_DOWN
        animateChildTo(child, height, EXIT_ANIMATION_DURATION, AnimationUtils.FAST_OUT_LINEAR_IN_INTERPOLATOR)
    }

    private fun animateChildTo(child: V, targetY: Int, duration: Long, interpolator: TimeInterpolator) {
        currentAnimator = child.animate()
                .translationY(targetY.toFloat())
                .setInterpolator(interpolator)
                .setDuration(duration)
                .setListener(object : AnimatorListenerAdapter() {
                    override fun onAnimationEnd(animation: Animator) {
                        currentAnimator = null
                    }
                })
    }

    /**
     * Edge case when expandable RecyclerView is collapsed and can't be scrolled
     */
    private fun assureBottomViewVisibility(target: View, child: V) {
        val recycler = target as? RecyclerView
        recycler?.viewTreeObserver?.addOnGlobalLayoutListener(object : OnGlobalLayoutListener {
            override fun onGlobalLayout() {
                recycler.viewTreeObserver.removeOnGlobalLayoutListener(this)
                if (!recycler.canScrollVertically(DOWN) && !recycler.canScrollVertically(UP)) {
                    slideUp(child)
                }
            }
        })
    }
}

private const val ENTER_ANIMATION_DURATION = 225L
private const val EXIT_ANIMATION_DURATION = 175L
private const val STATE_SCROLLED_DOWN = 1
private const val STATE_SCROLLED_UP = 2
private const val DOWN = 1
private const val UP = -1