最近新業(yè)務(wù)要求集币，在ViewPager2 的item中考阱，再放一個(gè)ViewPager2用來展示Banner效果。發(fā)現(xiàn)兩個(gè)嵌套之后鞠苟，內(nèi)部的ViewPager2無法滑動(dòng)羔砾，首先考慮的就是滑動(dòng)沖突，打算重寫ViewPager2偶妖，修改onInterceptTouchEvent方法。卻發(fā)現(xiàn)ViewPager2是final修飾政溃，無法繼承重寫趾访。只能考慮別的方法。
后來董虱，在ViewPager2官方文檔中找到這么不起眼的一小段
大致意思就是：ViewPager2 嵌套在相同方向的滾動(dòng)View中是不能滾動(dòng)的扼鞋，如果需要滾動(dòng)ViewPager2申鱼，就需要調(diào)用requestDisallowInterceptTouchEvent，才可以接受到滑動(dòng)事件云头。
而且Google還給出了方案：views-widgets-samples/NestedScrollableHost.kt at master · android/views-widgets-samples · GitHub
我把代碼也貼出來捐友，簡單看下原理
/**
* 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)
}
}
}
}
}
}
用法也很簡單，用NestedScrollableHost把內(nèi)部ViewPager2包裹起來就可以啦溃槐。
我們主動(dòng)包裹住內(nèi)部ViewPager2后匣砖，就代表著需要處理事件了，所以在onInterceptTouchEvent函數(shù)中昏滴，如果接受到了DOWN事件猴鲫，就需要調(diào)用requestDisallowInterceptTouchEvent通知外層的ViewPager2不要攔截事件，讓我們的Host來處理滑動(dòng)事件谣殊。
等到MOVE事件進(jìn)來后拂共，判斷一下能不能順著手勢滑動(dòng)內(nèi)部的ViewPager2？
不能就不給內(nèi)部ViewPager2后續(xù)事件了（主動(dòng)通知外部ViewPager2攔截事件）姻几。
Host的作用就相當(dāng)于是一個(gè)開關(guān)在兩個(gè)ViewPager2之間宜狐。當(dāng)內(nèi)部的還可以滑動(dòng)，就允許事件傳遞下去蛇捌，當(dāng)內(nèi)部無法在手勢方向滑動(dòng)抚恒，就通知外部View進(jìn)行事件攔截。
完美解決了ViewPager2的嵌套問題豁陆。
按照這一思想柑爸，對(duì)于好多滑動(dòng)沖突的問題，都可以不用繼承盒音，直接寫一個(gè)Host來解決嵌套問題
