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Used OnTouchListener for nested scrolling in ViewPager2 #112

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Used OnTouchListener for nested scrolling in ViewPager2 #112

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72 changes: 30 additions & 42 deletions ViewPager2/app/src/main/java/androidx/viewpager2/integration/testapp/NestedScrollableHost.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -16,77 +16,62 @@

package androidx.viewpager2.integration.testapp

import android.annotation.SuppressLint
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 android.view.*
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
* Class to scroll 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.
* ViewPager2.
*
* 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 class NestedScrollableHost(context: Context) : View.OnTouchListener {

private var touchSlop = 0
private var touchSlop = ViewConfiguration.get(context).scaledTouchSlop
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
private val View.parentViewPager: ViewPager2?
get() = generateSequence(this as? ViewParent, ViewParent::getParent)
.filterIsInstance<ViewPager2>()
.firstOrNull()

init {
touchSlop = ViewConfiguration.get(context).scaledTouchSlop
}

private fun canChildScroll(orientation: Int, delta: Float): Boolean {
private fun View.canScroll(orientation: Int, delta: Float): Boolean {
val direction = -delta.sign.toInt()
return when (orientation) {
0 -> child?.canScrollHorizontally(direction) ?: false
1 -> child?.canScrollVertically(direction) ?: false
ViewPager2.ORIENTATION_HORIZONTAL -> canScrollHorizontally(direction)
ViewPager2.ORIENTATION_VERTICAL -> canScrollVertically(direction)
else -> throw IllegalArgumentException()
}
}

override fun onInterceptTouchEvent(e: MotionEvent): Boolean {
handleInterceptTouchEvent(e)
return super.onInterceptTouchEvent(e)
@SuppressLint("ClickableViewAccessibility")
override fun onTouch(view: View, e: MotionEvent): Boolean {
handleInterceptTouchEvent(view, e)
return false
}

private fun handleInterceptTouchEvent(e: MotionEvent) {
val orientation = parentViewPager?.orientation ?: return
private fun handleInterceptTouchEvent(view: View, e: MotionEvent) {
val orientation = view.parentViewPager?.orientation ?: return

// Early return if child can't scroll in same direction as parent
if (!canChildScroll(orientation, -1f) && !canChildScroll(orientation, 1f)) {
if (!view.canScroll(orientation, -1f) && !view.canScroll(orientation, 1f)) {
return
}

if (e.action == MotionEvent.ACTION_DOWN) {
initialX = e.x
initialY = e.y
parent.requestDisallowInterceptTouchEvent(true)
view.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
val isVpHorizontal = orientation == ViewPager2.ORIENTATION_HORIZONTAL

// assuming ViewPager2 touch-slop is 2x touch-slop of child
val scaledDx = dx.absoluteValue * if (isVpHorizontal) .5f else 1f
Expand All @@ -95,18 +80,21 @@ class NestedScrollableHost : FrameLayout {
if (scaledDx > touchSlop || scaledDy > touchSlop) {
if (isVpHorizontal == (scaledDy > scaledDx)) {
// Gesture is perpendicular, allow all parents to intercept
parent.requestDisallowInterceptTouchEvent(false)
view.parent.requestDisallowInterceptTouchEvent(false)
} else {
// Gesture is parallel, query child if movement in that direction is possible
if (canChildScroll(orientation, if (isVpHorizontal) dx else dy)) {
if (view.canScroll(orientation, if (isVpHorizontal) dx else dy)) {
// Child can scroll, disallow all parents to intercept
parent.requestDisallowInterceptTouchEvent(true)
view.parent.requestDisallowInterceptTouchEvent(true)
} else {
// Child cannot scroll, allow all parents to intercept
parent.requestDisallowInterceptTouchEvent(false)
view.parent.requestDisallowInterceptTouchEvent(false)
}
}
}
}
}
}
}

fun ViewGroup.allowSameDirectionScrollingInViewPager2() =
setOnTouchListener(NestedScrollableHost(context))
1 change: 1 addition & 0 deletions .../src/main/java/androidx/viewpager2/integration/testapp/ParallelNestedScrollingActivity.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,7 @@ class ParallelNestedScrollingActivity : Activity() {
private fun RecyclerView.setUpRecyclerView(orientation: Int) {
layoutManager = LinearLayoutManager(context, orientation, false)
adapter = RvAdapter(orientation)
allowSameDirectionScrollingInViewPager2()
}

class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
Expand Down
27 changes: 9 additions & 18 deletions ViewPager2/app/src/main/res/layout/item_nested_recyclerviews.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -40,16 +40,12 @@
android:text="@string/first_rv"
android:textStyle="bold" />

<androidx.viewpager2.integration.testapp.NestedScrollableHost
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/first_rv"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="8dp">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/first_rv"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#FFFFFF" />
</androidx.viewpager2.integration.testapp.NestedScrollableHost>
android:layout_marginTop="8dp"
android:background="#FFFFFF" />

<TextView
android:layout_width="match_parent"
Expand All @@ -60,18 +56,13 @@
android:text="@string/second_rv"
android:textStyle="bold" />

<androidx.viewpager2.integration.testapp.NestedScrollableHost
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/second_rv"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_height="match_parent"
android:layout_marginLeft="20dp"
android:layout_marginRight="20dp"
android:layout_marginTop="8dp"
android:layout_weight="1">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/second_rv"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#FFFFFF" />
</androidx.viewpager2.integration.testapp.NestedScrollableHost>
android:layout_marginRight="20dp"
android:background="#FFFFFF" />

</LinearLayout>