RecyclerView 添加Header

效果图：

原理：将Header当成普通的item添加上去

onAttachtoRecyclerView方法：判断position位置的item是不是Header,如果是Header则返回gridManager.getSpanCount()（表示当前item占据spanCount个单元格），否则占据1个单元格。@Override    public void onAttachedToRecyclerView(RecyclerView recyclerView) {        super.onAttachedToRecyclerView(recyclerView);       RecyclerView.LayoutManager manager = recyclerView.getLayoutManager();        if (manager instanceof GridLayoutManager) {           final GridLayoutManager gridManager = ((GridLayoutManager) manager);            gridManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {                @Override                public int getSpanSize(int position) {                 return getItemViewType(position) == TYPE_HEADER                            ? gridManager.getSpanCount() : 1;                }            });        }    }//position==0，返回Header    @Override    public int getItemViewType(int position) {        if (position == 0) return TYPE_HEADER;        else {        ......           }    }//根据viewType 确定返回Header或是普通item    @Override    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {        View view;        if (viewType == TYPE_HEADER) {            view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_header_homepage, parent, false);            return new HeaderViewHolder(view);        }        if (viewType == VIEW_TYPE_ONE) {            view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_onepic_homepage, parent, false);            return new HomePageOnePicViewHolder(view);        } else {            view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_threepic_homepage, parent, false);            return new HomePageThreePicViewHolder(view);        }    }    @Override    public void onBindViewHolder(final ViewHolder holder, int position) {        if (holder.getItemViewType() == TYPE_HEADER) {            final HeaderViewHolder headerViewHolder = (HeaderViewHolder) holder;            ......            return;        }        final int pos = getRealPosition(holder);        final UserHomePageBean userHomePageItem = userHomePageBeanList.get(pos);        if (holder.getItemViewType() == VIEW_TYPE_THREE) {            HomePageThreePicViewHolder homePageThreePicViewHolder = (HomePageThreePicViewHolder) holder;            ......            }        }  //因为item的总数量是根据beanList判断的，添加了Header但是并没有在beanList中增加（因为数据结构不一致），所以添加了Header后itemCount应该加1          @Override    public int getItemCount() {        return mHeaderView == false ? userHomePageBeanList.size() : userHomePageBeanList.size() + 1;    }//得到真正的position,因为在onBindView里要根据position来获得对应位置的beanList的数据,添加了Header之后，元素个数增加了1个，所以用原来的position得到的bean并不是对应位置的bean，而是正确的bean的后一个。所以如果添加了Header，实际position应该是原来的减1。    public int getRealPosition(ViewHolder holder) {        int position = holder.getLayoutPosition();        return mHeaderView == false ? position : position - 1;    }