处理Viewpager2嵌套滑动问题

使用NestedScrollableHost 将子view中需要滑动的recyclerview等滑动view 套一层
/*

• 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.testapp

import 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 = 0
  private var initialX = 0f
  private var initialY = 0f
  private val parentViewPager: ViewPager2?
  get() {
  var v: View? = parent as? View
  while (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 null

  init {
  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) ?: false
  1 -> child?.canScrollVertically(direction) ?: false
  else -> 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 parent
   if (!canChildScroll(orientation, -1f) && !canChildScroll(orientation, 1f)) {
       return
   }
  
   if (e.action == MotionEvent.ACTION_DOWN) {
       initialX = e.x
       initialY = e.y
       parent.requestDisallowInterceptTouchEvent(true)
   } else if (e.action == MotionEvent.ACTION_MOVE) {
       val dx = e.x - initialX
       val dy = e.y - initialY
       val isVpHorizontal = orientation == ORIENTATION_HORIZONTAL
  
       // assuming ViewPager2 touch-slop is 2x touch-slop of child
       val scaledDx = dx.absoluteValue * if (isVpHorizontal) .5f else 1f
       val scaledDy = dy.absoluteValue * if (isVpHorizontal) 1f else .5f
  
       if (scaledDx > touchSlop || scaledDy > touchSlop) {
           if (isVpHorizontal == (scaledDy > scaledDx)) {
               // Gesture is perpendicular, allow all parents to intercept
               parent.requestDisallowInterceptTouchEvent(false)
           } else {
               // Gesture is parallel, query child if movement in that direction is possible
               if (canChildScroll(orientation, if (isVpHorizontal) dx else dy)) {
                   // Child can scroll, disallow all parents to intercept
                   parent.requestDisallowInterceptTouchEvent(true)
               } else {
                   // Child cannot scroll, allow all parents to intercept
                   parent.requestDisallowInterceptTouchEvent(false)
               }
           }
       }
   }
  

  }
  }