如何在选择时将项目设置为Recycler视图的中心

Question

我用a RecyclerView来水平显示项目.我想将所选项目设置为视图的中心,如下所示

.

这就是我这样做的方式:

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

Answer 1

这是用于在滚动时或单击某个项目时在中心对齐项目。

您需要将 SnapHelper 添加到 RecyclerView。方法如下：

final RecyclerView recyclerViewObject = view.findViewById(R.id.recyclerViewObjectId);

final LinearSnapHelper snapHelper = new LinearSnapHelper();
snapHelper.attachToRecyclerView(recyclerViewObject);

recyclerViewObject.setOnFlingListener(snapHelper);

那么你只需调用此代码

recyclerViewObject.addOnItemTouchListener(
            new RecyclerItemClickListener(getContext(), recyclerViewObject ,new RecyclerItemClickListener.OnItemClickListener() {
                @Override public void onItemClick(View view, int position) {
                    recyclerViewObject.smoothScrollToPosition(position);
                }

                @Override public void onLongItemClick(View view, int position) {
                }
            })
    );

Answer 2

要从RecyclerView获取屏幕上的中间项目，可以将OnScrollListener附加到RecyclerView上，在侦听器内部，您应该获取当前项目的位置，然后检查给定项目的区域是否在屏幕中间。

Kotlin中的代码示例：

// 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，您应该得到如下内容：

Answer 3

您可以使用最少的代码行实现相同的输出。其中，view是所选适配器项目的视图，StaticData.SCREEN_WIDTH是设备宽度。

    View view = rvCategory.getChildAt(pos);
    if (view == null)
        return;
    int scrollX = (view.getLeft() - (StaticData.SCREEN_WIDTH / 2)) + (view.getWidth() / 2);
    rvCategory.smoothScrollBy(scrollX, 0);

Answer 4

请尝试以下解决方案：

LinearLayoutManager layoutManager = ((LinearLayoutManager)recyclerView.getLayoutManager());
int totalVisibleItems = layoutManager.findLastVisibleItemPosition() - layoutManager.findFirstVisibleItemPosition()    
int centeredItemPosition = totalVisibleItems / 2;
    recyclerView.smoothScrollToPosition(position);
    recyclerView.setScrollY(centeredItemPosition );

希望这可以帮助。