RecyclerView检测滑动到顶部或底部的代码示例

在使用RecyclerView时，经常需要检测用户是否滑动到顶部或底部

  private void addOnScrollListener() {
        //为RecyclerView添加OnScrollListener，监控滑动事件
        mPhotoRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            private int lastVisibleItemPosition;
            private int firstVisibleItemPosition;

            //滑动结束时，将回调onScrolled接口
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy){
                super.onScrolled(recyclerView, dx, dy);

                RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();

                if (layoutManager instanceof GridLayoutManager) {
                    //得到当前界面，最后一个子视图对应的position
                    lastVisibleItemPosition = ((GridLayoutManager) layoutManager)
                            .findLastVisibleItemPosition();

                    //得到当前界面，第一个子视图的position
                    firstVisibleItemPosition = ((GridLayoutManager) layoutManager)
                            .findFirstVisibleItemPosition();

                    ................
                }
            }

            //当滑动状态发生改变时，回调该接口
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);

                RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();

                //得到当前界面可见数据的大小
                int visibleItemCount = layoutManager.getChildCount();

                //得到RecyclerView对应所有数据的大小
                int totalItemCount = layoutManager.getItemCount();

                //判断条件可按实际需要调整
                if (newState == RecyclerView.SCROLL_STATE_IDLE && visibleItemCount > 0) {

                    //最后视图对应的position等于总数-1时，说明上一次滑动结束时，触底了
                    if (lastVisibleItemPosition == totalItemCount - 1){
                        //按需进行业务
                        startURLLoader();

                    //第一个视图的position等于0，说明上一次滑动结束时，触顶了
                    } else if (firstVisibleItemPosition == 0) {
                        Toast.makeText(getActivity(),
                                "Already to the top",
                                Toast.LENGTH_SHORT)
                                .show();
                    }
                }
            }
        });
   }