老规矩直接上代码， 不分析：
import android.content.Context
import android.util.AttributeSet
import android.view.MotionEvent
import android.view.View
import android.view.ViewConfiguration
import android.view.ViewGroup
import android.widget.FrameLayout
import androidx.recyclerview.widget.RecyclerView
import androidx.viewpager2.widget.ViewPager2
import kotlin.math.abs
import kotlin.math.absoluteValue
import kotlin.math.sign/** Copyright 2019 The Android Open Source Project** Licensed under the Apache License, Version 2.0 (the "License");* you may not use this file except in compliance with the License.* You may obtain a copy of the License at** http://www.apache.org/licenses/LICENSE-2.0** Unless required by applicable law or agreed to in writing, software* distributed under the License is distributed on an "AS IS" BASIS,* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.* See the License for the specific language governing permissions and* limitations under the License.*//*** Layout to wrap a scrollable component inside a ViewPager2. Provided as a solution to the problem* where pages of ViewPager2 have nested scrollable elements that scroll in the same direction as* ViewPager2. The scrollable element needs to be the immediate and only child of this host layout.** This solution has limitations when using multiple levels of nested scrollable elements* (e.g. a horizontal RecyclerView in a vertical RecyclerView in a horizontal ViewPager2).*/
class NestedScrollableHost : FrameLayout {constructor(context: Context) : super(context)constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)private var touchSlop = 0private var initialX = 0fprivate var initialY = 0fprivate val parentViewPager: ViewPager2?get() {var v: View? = parent as? Viewwhile (v != null && v !is ViewPager2) {v = v.parent as? View}return v as? ViewPager2}private val child: View? get() = if (childCount > 0) getChildAt(0) else nullinit {touchSlop = ViewConfiguration.get(context).scaledTouchSlop}private fun canChildScroll(orientation: Int, delta: Float): Boolean {val direction = -delta.sign.toInt()return when (orientation) {0 -> child?.canScrollHorizontally(direction) ?: false1 -> child?.canScrollVertically(direction) ?: falseelse -> throw IllegalArgumentException()}}override fun onInterceptTouchEvent(e: MotionEvent): Boolean {handleInterceptTouchEvent(e)return super.onInterceptTouchEvent(e)}private fun handleInterceptTouchEvent(e: MotionEvent) {val orientation = parentViewPager?.orientation ?: return// Early return if child can't scroll in same direction as parentif (!canChildScroll(orientation, -1f) && !canChildScroll(orientation, 1f)) {return}if (e.action == MotionEvent.ACTION_DOWN) {initialX = e.xinitialY = e.yparent?.requestDisallowInterceptTouchEvent(true)} else if (e.action == MotionEvent.ACTION_MOVE) {val dx = e.x - initialXval dy = e.y - initialYval isVpHorizontal = orientation == RecyclerView.HORIZONTAL// assuming ViewPager2 touch-slop is 2x touch-slop of childval scaledDx = dx.absoluteValue * if (isVpHorizontal) .5f else 1fval scaledDy = dy.absoluteValue * if (isVpHorizontal) 1f else .5fif (scaledDx > touchSlop || scaledDy > touchSlop) {if (isVpHorizontal == (scaledDy > scaledDx)) {// Gesture is perpendicular, allow all parents to interceptparent?.requestDisallowInterceptTouchEvent(false)} else {// Gesture is parallel, query child if movement in that direction is possibleif (canChildScroll(orientation, if (isVpHorizontal) dx else dy)) {// Child can scroll, disallow all parents to interceptparent?.requestDisallowInterceptTouchEvent(true)} else {// Child cannot scroll, allow all parents to interceptparent?.requestDisallowInterceptTouchEvent(false)}}}}}}/** Copyright 2019 The Android Open Source Project** Licensed under the Apache License, Version 2.0 (the "License");* you may not use this file except in compliance with the License.* You may obtain a copy of the License at** http://www.apache.org/licenses/LICENSE-2.0** Unless required by applicable law or agreed to in writing, software* distributed under the License is distributed on an "AS IS" BASIS,* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.* See the License for the specific language governing permissions and* limitations under the License.*/package androidx.viewpager2.integration.testappimport android.content.Context
import android.util.AttributeSet
import android.view.MotionEvent
import android.view.View
import android.view.ViewConfiguration
import android.widget.FrameLayout
import androidx.viewpager2.widget.ViewPager2
import androidx.viewpager2.widget.ViewPager2.ORIENTATION_HORIZONTAL
import kotlin.math.absoluteValue
import kotlin.math.sign/*** Layout to wrap a scrollable component inside a ViewPager2. Provided as a solution to the problem* where pages of ViewPager2 have nested scrollable elements that scroll in the same direction as* ViewPager2. The scrollable element needs to be the immediate and only child of this host layout.** This solution has limitations when using multiple levels of nested scrollable elements* (e.g. a horizontal RecyclerView in a vertical RecyclerView in a horizontal ViewPager2).*/
class NestedScrollableHost : FrameLayout {constructor(context: Context) : super(context)constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)private var touchSlop = 0private var initialX = 0fprivate var initialY = 0fprivate val parentViewPager: ViewPager2?get() {var v: View? = parent as? Viewwhile (v != null && v !is ViewPager2) {v = v.parent as? View}return v as? ViewPager2}private val child: View? get() = if (childCount > 0) getChildAt(0) else nullinit {touchSlop = ViewConfiguration.get(context).scaledTouchSlop}private fun canChildScroll(orientation: Int, delta: Float): Boolean {val direction = -delta.sign.toInt()return when (orientation) {0 -> child?.canScrollHorizontally(direction) ?: false1 -> child?.canScrollVertically(direction) ?: falseelse -> throw IllegalArgumentException()}}override fun onInterceptTouchEvent(e: MotionEvent): Boolean {handleInterceptTouchEvent(e)return super.onInterceptTouchEvent(e)}private fun handleInterceptTouchEvent(e: MotionEvent) {val orientation = parentViewPager?.orientation ?: return// Early return if child can't scroll in same direction as parentif (!canChildScroll(orientation, -1f) && !canChildScroll(orientation, 1f)) {return}if (e.action == MotionEvent.ACTION_DOWN) {initialX = e.xinitialY = e.yparent.requestDisallowInterceptTouchEvent(true)} else if (e.action == MotionEvent.ACTION_MOVE) {val dx = e.x - initialXval dy = e.y - initialYval isVpHorizontal = orientation == ORIENTATION_HORIZONTAL// assuming ViewPager2 touch-slop is 2x touch-slop of childval scaledDx = dx.absoluteValue * if (isVpHorizontal) .5f else 1fval scaledDy = dy.absoluteValue * if (isVpHorizontal) 1f else .5fif (scaledDx > touchSlop || scaledDy > touchSlop) {if (isVpHorizontal == (scaledDy > scaledDx)) {// Gesture is perpendicular, allow all parents to interceptparent.requestDisallowInterceptTouchEvent(false)} else {// Gesture is parallel, query child if movement in that direction is possibleif (canChildScroll(orientation, if (isVpHorizontal) dx else dy)) {// Child can scroll, disallow all parents to interceptparent.requestDisallowInterceptTouchEvent(true)} else {// Child cannot scroll, allow all parents to interceptparent.requestDisallowInterceptTouchEvent(false)}}}}}
}
