RecyclerView 监听滑动条滚动事件触发load more

//倒数第几个开始加载
    private int mCountDown = 1;
    //上一次加载点 所在recyclerview 中的位置
    private int mExLoadPos = -1;

    private OnLoadMore mOnLoadMore;


    private LinearLayoutManager mLinearLayoutManager;

    public EndlessRecyclerOnScrollListener(LinearLayoutManager linearLayoutManager, OnLoadMore onLoadMore) {
        this.mLinearLayoutManager = linearLayoutManager;
        mOnLoadMore = onLoadMore;
    }

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);

        int loadPos = recyclerView.getAdapter().getItemCount() - mCountDown;
        //最后一个可见视图在 recyclerview  中的位置
        int lvvPos = mLinearLayoutManager.findLastVisibleItemPosition();
//        System.out.println("last:" + mExLoadPos + " loadpos:" + loadPos + " lvvPos:" + lvvPos + " dy:" + dy);
        //当指定 加载点视图 小于等于最后可见视图，且 向下滑动； 加载机会
        if (dy > 0 && loadPos <= lvvPos) {
            doLoadMore(loadPos);
        }

    }

    private synchronized void doLoadMore(int loadPos) {
        if (mExLoadPos != loadPos) {
            //如果上一次加载点 和本次加载点不同，则可以加载,含括 lastloadpos > loadpos && lastloadpos < loadpos
//            System.out.println("start load more");
            mExLoadPos = loadPos;
            mOnLoadMore.onLoadMore();
        }
    }

    public interface OnLoadMore {
        void onLoadMore();
    }

    public int getmCountDown() {
        return mCountDown;
    }

    public void setmCountDown(int mCountDown) {
        this.mCountDown = mCountDown;
    }