https://issuetracker.google.com/issues/148731508

NestedScrollingWebView.kt

import android.content.Context
import android.util.AttributeSet
import android.util.Log
import android.view.MotionEvent
import android.view.View
import android.webkit.WebView
import androidx.customview.widget.ViewDragHelper

class NestedScrollingWebView @JvmOverloads constructor(context: Context,
                                                       attrs: AttributeSet? = null) : WebView(context, attrs) {
    companion object {
        private val TAG = "NestedScrollingWebView"
    }
    private var isBeingDragged = false
    private var activePointerId = ViewDragHelper.INVALID_POINTER
    private var lastMotionX = 0f
    private var lastMotionY = 0f
    private var nestedXOffset = 0f
    private var nestedYOffset = 0f
    // object-local variables for receiving output, hurray for JVM
    private val scrollConsumed = IntArray(2)

    init {
        // ...because why else would you be using this widget?
        isNestedScrollingEnabled = true
    }

    override fun overScrollBy(deltaX: Int, deltaY: Int, scrollX: Int, scrollY: Int,
                              scrollRangeX: Int, scrollRangeY: Int, maxOverScrollX: Int, maxOverScrollY: Int,
                              isTouchEvent: Boolean): Boolean {
//        Log.d("TRACKME", "$deltaX, $deltaY, $scrollX, $scrollY, $scrollRangeX, $scrollRangeY, $maxOverScrollX, $maxOverScrollY, $isTouchEvent")
        return dispatchNestedScroll(0, 0, deltaX, deltaY, null) || super.overScrollBy(
            deltaX, deltaY, scrollX, scrollY, scrollRangeX, scrollRangeY, maxOverScrollX, maxOverScrollY, isTouchEvent)
    }

    override fun onTouchEvent(ev: MotionEvent): Boolean {
        when (ev.actionMasked) {
            MotionEvent.ACTION_DOWN -> {
                parent?.requestDisallowInterceptTouchEvent(true)
                activePointerId = ev.getPointerId(0)
                isBeingDragged = true
                lastMotionX = ev.x
                lastMotionY = ev.y
                nestedXOffset = 0f
                nestedYOffset = 0f
                startNestedScroll(View.SCROLL_AXIS_VERTICAL)
            }
            MotionEvent.ACTION_MOVE -> if (isBeingDragged) {
                val activePointerIndex = ev.findPointerIndex(activePointerId)
                if (activePointerIndex == -1) {
                    Log.e(TAG, "Invalid pointerId=$activePointerId in onInterceptTouchEvent")
                } else {
                    parent?.requestDisallowInterceptTouchEvent(true)
                    val x = ev.getX(activePointerIndex)
                    val y = ev.getY(activePointerIndex)
                    if (dispatchNestedPreScroll((lastMotionX - x).toInt(), (lastMotionY - y).toInt(), scrollConsumed, null)) {
//                        Log.d(TAG, "nested ${scrollConsumed.joinToString()}, $nestedYOffset")
                        nestedXOffset += scrollConsumed[0]
                        nestedYOffset += scrollConsumed[1]
                    }
                    lastMotionX = x
                    lastMotionY = y
                    // dispatchNestedScroll will later be called by overScrollBy, as a result of super.onTouchEvent
                }
            }
            MotionEvent.ACTION_CANCEL, MotionEvent.ACTION_UP -> {
                activePointerId = ViewDragHelper.INVALID_POINTER
                isBeingDragged = false
                stopNestedScroll()
                nestedXOffset = 0f
                nestedYOffset = 0f
            }
        }
        val vtev = MotionEvent.obtain(ev)
        vtev.offsetLocation(nestedXOffset, nestedYOffset)
        super.onTouchEvent(vtev)
        return true
    }
}