RecyclerView SnapHelper 无法显示第一个/最后一个项目

我有一个RecyclerView它附加到一个LinearSnapHelper捕捉到中心项目。当我滚动到第一个或最后一个项目时，这些项目不再完全可见。此问题如下图所示。怎么解决呢？

一个迟到的答案只是用Java代码编写的：

Create CustomSnapHelper class:

 public class CustomSnapHelper extends LinearSnapHelper {
        @Override
        public View findSnapView(RecyclerView.LayoutManager layoutManager) {
            if(layoutManager instanceof LinearLayoutManager){
                LinearLayoutManager linearLayoutManager = (LinearLayoutManager) layoutManager;
                if(needToDoSnap(linearLayoutManager)==false){
                    return null;
                }
            }
            return super.findSnapView(layoutManager);
        }
        public boolean needToDoSnap(LinearLayoutManager linearLayoutManager){
            return linearLayoutManager.findFirstCompletelyVisibleItemPosition()!=0&&linearLayoutManager.findLastCompletelyVisibleItemPosition()!=linearLayoutManager.getItemCount()-1;
        }
    }

附加一个对象CustomSnapHelper到回收者视图：

CustomSnapHelper mSnapHelper = new CustomSnapHelper();
mSnapHelper.attachToRecyclerView(mRecyclerView);