在不改变滚动位置的情况下动态更新 Recyclerview 项目的布局

Question

场景： 我有一个卡片列表，基本上是一个 RecyclerView，Recycler 视图中只有两个项目。我也在扩展 RecyclerView.LayoutManager() 并覆盖 LayoutManager 类的 onLayoutChildren() 方法。 最初第二张卡片在底部，当我向上滑动时，第二张卡片滚动到顶部，就在第一张卡片下方一点点。

单击第二张卡片（列表中的第二项）中的“生成条形码”按钮时，我隐藏该按钮并显示替换该按钮的条形码图像。更新卡片布局时，会自动调用 onLayoutChildren() 方法。此方法被覆盖以在回收器视图启动时在特定位置显示卡片。这会导致布局管理器重绘子视图。因此，第二张卡片正在滚动回初始位置。

预期行为：当我们尝试更新第二张卡片布局时，第二张卡片不应向下滚动。

StackCardLayoutManager.kt

class StackCardLayoutManager(
    private val maxItemCount: Int
) : RecyclerView.LayoutManager() {
private val addedChildren: List<View>
    get() = (0 until childCount).map { getChildAt(it) ?: throw NullPointerException() }
private var firstTime: Boolean = true

init {
    Log.d(TAG_K, "StackCardLayoutManager.init()")
}

override fun generateDefaultLayoutParams(): RecyclerView.LayoutParams =
        RecyclerView.LayoutParams(RecyclerView.LayoutParams.WRAP_CONTENT, RecyclerView.LayoutParams.MATCH_PARENT)

override fun isAutoMeasureEnabled(): Boolean = true

override fun onLayoutChildren(
        recycler: RecyclerView.Recycler,
        state: RecyclerView.State
) {
    Log.d(TAG_K, "StackCardLayoutManager.onLayoutChildren(itemcount : ${state.itemCount}) addedChildren Size : ${addedChildren.size} firstTime : $firstTime")
    firstTime = false
    if (state.itemCount == 0) {
        return
    }

    if (state.itemCount > maxItemCount) {
        throw RuntimeException("Can not set more Item than $maxItemCount")
    }
    detachAndScrapAttachedViews(recycler)

    for (i in 0 until state.itemCount) {
        Log.d(TAG_K, "StackCardLayoutManager.onLayoutChildren($i) - layoutDecorated")
        val view = recycler.getViewForPosition(i)
        measureChild(view, 0, 0)
        addView(view)
        val layoutParams = view.layoutParams as RecyclerView.LayoutParams
        val left = layoutParams.marginStart
        Log.d(TAG_K, "StackCardLayoutManager.onLayoutChildren() left  : $left")
        val top = (view.measuredHeight * i * 1.15).toInt()
        Log.d(TAG_K, "StackCardLayoutManager.onLayoutChildren() top  : $top")
        val right = view.measuredWidth + layoutParams.marginEnd
        Log.d(TAG_K, "StackCardLayoutManager.onLayoutChildren() right  : $right")
        val bottom = top + view.measuredHeight
        Log.d(TAG_K, "StackCardLayoutManager.onLayoutChildren() bottom  : $bottom")
        layoutDecorated(view, left, top, right, bottom)
        view.setTag(InitializedPosition.TOP.key, top)
    }
}

override fun canScrollVertically(): Boolean = true

override fun scrollVerticallyBy(
        dy: Int,
        recycler: RecyclerView.Recycler,
        state: RecyclerView.State
): Int = dy.also { deltaY ->
    Log.d("stackcardlayout", "scrollVerticallyBy: $deltaY")
    if (childCount == 0) {
        Log.d("stackcardlayout", "scrollVerticallyBy: child count is 0")
        return@also
    }
    var deltaY1 = 0
    addedChildren.forEachIndexed { index, view ->
        val initializedTop = view.getTag(InitializedPosition.TOP.key) as Int
        val layoutParams = view.layoutParams as RecyclerView.LayoutParams
        val left = layoutParams.marginStart

        if(deltaY < 0){
            deltaY1 = -500
        }else {
            deltaY1 = 500
        }

        val top = min(max((view.top - deltaY1), index * dpToPx(70)), initializedTop)
        val right = view.measuredWidth + layoutParams.marginEnd
        val bottom = top + view.measuredHeight
        layoutDecorated(view, left, top, right, bottom)
    }
}

private enum class InitializedPosition(val key: Int) {
    TOP(R.integer.top)
}
}

我尝试在这个解决方案周围搜索并在Stackoverflow 上发现了类似的问题，但是该解决方案对 androidx Recyclerview 无效，但仅对 android v7 Recycyler 视图支持库有效。

Answer 1

我看到了答案。建议您按照eatRequestLayout() 方法来实现你的自定义视图requestLayout方法。

// RecyclerView requestlayout
@Override
    public void requestLayout() {
        if (!mEatRequestLayout) {
            super.requestLayout();
        } else {
            mLayoutRequestEaten = true;
        }
    }
//RecyclerView.eatRequestLayout
void eatRequestLayout() {
        if (!mEatRequestLayout) {
            mEatRequestLayout = true;
            mLayoutRequestEaten = false;
        }
    }

由于文档中提到的requestLayout，视图根据它重新绘制

当某些事情发生变化而导致该视图的布局无效时调用它。这将安排视图树的布局传递。

在您的自定义视图requestLayout中，您可以根据自己的情况，设置不同的标志来防止重绘。