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Fix parallel scroll with a NestedScrollView inside a ViewPager2
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| /* | |
| * 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 { | |
| return handleInterceptTouchEvent(e) || super.onInterceptTouchEvent(e) | |
| } | |
| /** | |
| * @return The child does not need to scroll. | |
| */ | |
| private fun handleInterceptTouchEvent(e: MotionEvent): Boolean { | |
| val orientation = parentViewPager?.orientation ?: return false | |
| // Early return if child can't scroll in same direction as parent | |
| if (!canChildScroll(orientation, -1f) && !canChildScroll(orientation, 1f)) { | |
| return false | |
| } | |
| 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 | |
| if (dx.absoluteValue > touchSlop || dy.absoluteValue > touchSlop) { | |
| if (isVpHorizontal == (dy.absoluteValue > dx.absoluteValue)) { | |
| // Gesture is perpendicular, allow all parents to intercept | |
| parent.requestDisallowInterceptTouchEvent(false) | |
| // If you are the following case: | |
| // ViewPager2(V) -> NestedScrollView(V) -> RecyclerView(H) | |
| // return false instead so that the innermost RV(H) can scroll normally. | |
| // It is not tested for other use case. | |
| return true | |
| } 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) | |
| return true | |
| } | |
| } | |
| } | |
| } | |
| return false | |
| } | |
| } |
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