android - 具有不同项目高度和 WRAP_CONTENT 的 ViewPager2

Question

有几篇文章介绍了如何让 ViewPager 处理以扩展 ViewPager 为中心的不同高度项目。自己修改其onMeasure支持这一点。
但是，鉴于 ViewPager2 被标记为最终类，扩展它不是我们可以做的事情。
有谁知道是否有办法解决这个问题？

例如。假设我有两种观点:
View 1 = 200dp
View 2 = 300dp
当 ViewPager2 (layout_height="wrap_content") 加载时——查看 View1，它的高度将为 200dp。
但是当我滚动到 View2 时，高度仍然是 200dp； View2 的最后 100dp 被截断。

Answer 1

解决办法是注册一个PageChangeCallback并调整 LayoutParams的ViewPager2在要求 child 重新测量自己之后。

pager.registerOnPageChangeCallback(object : ViewPager2.OnPageChangeCallback() {
    override fun onPageSelected(position: Int) {
        super.onPageSelected(position)
        val view = // ... get the view
        view.post {
            val wMeasureSpec = MeasureSpec.makeMeasureSpec(view.width, MeasureSpec.EXACTLY)
            val hMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED)
            view.measure(wMeasureSpec, hMeasureSpec)

            if (pager.layoutParams.height != view.measuredHeight) {
                // ParentViewGroup is, for example, LinearLayout
                // ... or whatever the parent of the ViewPager2 is
                pager.layoutParams = (pager.layoutParams as ParentViewGroup.LayoutParams)
                    .also { lp -> lp.height = view.measuredHeight }
            }
        }
    }
})

或者，如果您的 View 的高度可能由于例如异步数据加载，然后使用全局布局监听器代替:

pager.registerOnPageChangeCallback(object : ViewPager2.OnPageChangeCallback() {
    private val listener = ViewTreeObserver.OnGlobalLayoutListener {
        val view = // ... get the view
        updatePagerHeightForChild(view)
    }

    override fun onPageSelected(position: Int) {
        super.onPageSelected(position)
        val view = // ... get the view
        // ... IMPORTANT: remove the global layout listener from other views
        otherViews.forEach { it.viewTreeObserver.removeOnGlobalLayoutListener(layoutListener) }
        view.viewTreeObserver.addOnGlobalLayoutListener(layoutListener)
    }

    private fun updatePagerHeightForChild(view: View) {
        view.post {
            val wMeasureSpec = MeasureSpec.makeMeasureSpec(view.width, MeasureSpec.EXACTLY)
            val hMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED)
            view.measure(wMeasureSpec, hMeasureSpec)

            if (pager.layoutParams.height != view.measuredHeight) {
                // ParentViewGroup is, for example, LinearLayout
                // ... or whatever the parent of the ViewPager2 is
                pager.layoutParams = (pager.layoutParams as ParentViewGroup.LayoutParams)
                    .also { lp -> lp.height = view.measuredHeight }
            }
        }
    }
}

请参阅此处的讨论:
https://issuetracker.google.com/u/0/issues/143095219