how to show/hide FAB on scroll Recycler view with coordinator parent

Question

I have an activity with coordinator layout.inside activity there is a fragment with Recycler view and float button.how can I show/hide float button when Scroll Recycler view and

Answer 1

Here is working solution:

class HideOnScrollFabBehavior(context: Context?, attrs: AttributeSet?) : FloatingActionButton.Behavior() {

    // changes visibility from GONE to INVISIBLE when fab is hidden because
    // due to CoordinatorLayout.onStartNestedScroll() implementation
    // child view's (here, fab) onStartNestedScroll won't be called anymore
    // because it's visibility is GONE
    private val listener = object : FloatingActionButton.OnVisibilityChangedListener() {
        override fun onHidden(fab: FloatingActionButton?) {
            fab?.visibility = INVISIBLE
        }
    }

    override fun onStartNestedScroll(coordinatorLayout: CoordinatorLayout, child: FloatingActionButton, directTargetChild: View, target: View, axes: Int, type: Int): Boolean {
        return axes == ViewCompat.SCROLL_AXIS_VERTICAL // Ensure we react to vertical scrolling
                || super.onStartNestedScroll(coordinatorLayout, child, directTargetChild, target, axes, type)
    }

    override fun onNestedScroll(coordinatorLayout: CoordinatorLayout, child: FloatingActionButton, target: View, dxConsumed: Int, dyConsumed: Int, dxUnconsumed: Int, dyUnconsumed: Int, type: Int, consumed: IntArray) {
        super.onNestedScroll(coordinatorLayout, child, target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed, type, consumed)
        if (!target.canScrollVertically(1) && dyConsumed > 0 && child.visibility == VISIBLE) {
            // hide the FAB when scroll view reached its bottom
            child.hide(listener)
        } else if (dyConsumed < 0 && child.visibility != VISIBLE) {
            // show the FAB on scroll up
            child.show()
        }
    }

}