RecyclerView滑动距离计算

最近在写关于RecyclerView滑动到最底部时，给出一个判断，是否到达最底部。但不知道为什么，总是得不到ScrollY，一直为0。没办法，只能去网上找一些相关资料。
非常感谢知乎用户－张宇 给的想法。原理很简单，主要就是获取item的高度，和item的总数，然后去计算总的长度。


废话不多说，代码贴上：

    /**
     * 还能向下滑动多少
     */
    private int getDistance(){
        LinearLayoutManager layoutManager = (LinearLayoutManager) mRecyclerView.getLayoutManager();
        View firstVisibItem = mRecyclerView.getChildAt(0);
        int firstItemPosition = layoutManager.findFirstVisibleItemPosition();
        int itemCount = layoutManager.getItemCount();
        int recycleViewHeight = mRecyclerView.getHeight();
        int itemHeight = firstVisibItem.getHeight();
        int firstItemBottom = layoutManager.getDecoratedBottom(firstVisibItem);
        return (itemCount - firstItemPosition - 1)* itemHeight - recycleViewHeight+firstItemBottom;
    }

当前的getDistance()就是剩余的距离。

    /**
     * 已滑动的距离
     */
    private int getDistance(){
        LinearLayoutManager layoutManager = (LinearLayoutManager) mRecyclerView.getLayoutManager();
        View firstVisibItem = mRecyclerView.getChildAt(0);
        int firstItemPosition = layoutManager.findFirstVisibleItemPosition();
        int itemCount = layoutManager.getItemCount();
        int recycleViewHeight = mRecyclerView.getHeight();
        int itemHeight = firstVisibItem.getHeight();
        int firstItemBottom = layoutManager.getDecoratedBottom(firstVisibItem);
        return (firstItemPosition + 1)*itemHeight - firstItemBottom;
    }

计算RecyclerView已经滑动的距离。

    /**
     * 获取RecyclerView滚动距离
     */
    private int getDistance(){
        LinearLayoutManager layoutManager = (LinearLayoutManager) mRecyclerView.getLayoutManager();
        View firstVisibItem = mRecyclerView.getChildAt(0);
        int firstItemPosition = layoutManager.findFirstVisibleItemPosition();
        int itemCount = layoutManager.getItemCount();
        int recycleViewHeight = mRecyclerView.getHeight();
        int itemHeight = firstVisibItem.getHeight();
        int firstItemBottom = layoutManager.getDecoratedBottom(firstVisibItem);
        return (itemCount - firstItemPosition - 1)* itemHeight - recycleViewHeight;
    }