android - 选中时如何将项目设置为 Recycler View 的中心

Question

我正在使用 RecyclerView 水平显示项目。我想像这样将所选项目设置为 View 的中心

.

我是这样做的:

LinearLayoutManager layoutManager
                = new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);
        recyclerView.setLayoutManager(layoutManager);

Answer 1

要从 RecyclerView 获取屏幕中间的项目，您可以将 OnScrollListener 附加到 RecyclerView，在监听器中您应该获取当前项目的位置，然后您应该检查给定项目的区域是否在屏幕中间。

Kotlin 代码示例:

// Attach OnScrollListener to your RecyclerView
addOnScrollListener(object : RecyclerView.OnScrollListener() {
    override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
        recyclerView.post {
            selectMiddleItem()
        }
    }
})

// implementation of method that is called from OnScrollListener
private fun selectMiddleItem() {
    val firstVisibleIndex = layoutManager.findFirstVisibleItemPosition()
    val lastVisibleIndex = layoutManager.findLastVisibleItemPosition()
    val visibleIndexes = listOf(firstVisibleIndex..lastVisibleIndex).flatten()

    for (i in visibleIndexes) {
        val vh = findViewHolderForLayoutPosition(i)
        if (vh?.itemView == null) {
            continue
        }
        val location = IntArray(2)
        vh.itemView.getLocationOnScreen(location)
        val x = location[0]
        val halfWidth = vh.itemView.width * .5
        val rightSide = x + halfWidth
        val leftSide = x - halfWidth
        val isInMiddle = screenWidth * .5 in leftSide..rightSide
        if (isInMiddle) {
            // "i" is your middle index and implement selecting it as you want 
            // optionsAdapter.selectItemAtIndex(i)
            return
        }
    }
}

结果你应该得到这样的东西: