解决ViewPager2嵌套RecyclerView滑动冲突的问题

时间:2021-7-21 作者:qvyue

BUG分析

ViewPager2本事是由RecyclerView实现的,当垂直滑动的RecyclerView嵌套垂直滑动的RecyclerView时这本身就有冲突.

当然同向滑动的RecyclerView的嵌套都会有此问题

解决问题

知道了问题,其实就有了很多解决方式,我们解决滑动冲突的方式无非就是两种

  • 1.外部拦截法
  • 2.内部拦截法

但是这里我们是ViewPager2嵌套滑动,如果你查看源码你会发现:

public final class ViewPager2 extends ViewGroup {
      ````
}

看出问题了吗?,ViewPager2是用final修饰的而final修饰的就是告诉我们ViewPager2不能被继承
不知道Google出于什么考虑这样设定,这导致我们前面所说的外部拦截法失去了作用
对于ViewPager2来说我们只有一条路了内部拦截法

为了方便所以的滑动冲突,我们给内层的RecyclerView嵌套一层布局,通过通用布局来解决滑动冲突,这个布局是包裹内层滑动布局的

代码如下:

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)
                    }
                }
            }
        }
    }
}

ok. 试试你的问题解决没有

参考: ViewPager2文档

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