添加Footer的流程

1.getItemViewType—2.onCreateViewHolder—3.onBindViewHolder—4.getItemCount
对于是否加载footer的标志，应该在recyclerview滑动的时候来判断，所以传一个adapter。

public abstract class BaseListActivity<T> extends BaseActivity implements PullRecycler.onRecyclerRefreshListener {
    protected PullRecycler recycler;
    protected BaseListAdapter adapter;
    protected ArrayList<T> mDataList;


    @Override
    protected void setUpContentView() {
        setContentView(R.layout.activity_sample_list, R.string.sample_list_title);
    }


    @Override
    protected void setUpView() {
        recycler = (PullRecycler) findViewById(R.id.pullToRefreshRecycler);
    }

    @Override
    protected void setUpData() {
        adapter = new BaseListAdapter();
        recycler.setOnRefreshListener(this);
        recycler.setLayoutManager(getLayoutManager());
        recycler.addItemDecoration(getItemDecoration());
        recycler.setAdapter(adapter);

    }


    protected RecyclerView.ItemDecoration getItemDecoration() {
        return new DividerItemDecoration(getApplicationContext(), R.drawable.list_divider);
    }


    protected ILayoutManager getLayoutManager() {
        return new MyLinearLayoutManager(getApplicationContext());
    }


    class BaseListAdapter extends RecyclerView.Adapter<BaseViewHolder> {

        private static final int VIE_TYPE_LOAD_MORE_FOOTER = 100;
        private boolean isShowLoadMoreFooter;

        @Override
        public BaseViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            if (viewType == VIE_TYPE_LOAD_MORE_FOOTER) {
                return getLoadMoreFooter(parent);//加载不同布局
            }

            return getViewHolder(parent, viewType);
        }

        private BaseViewHolder getLoadMoreFooter(ViewGroup parent) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.widget_pull_to_refresh_footer, parent, false);
            return new LoadMoreFooterViewHolder(view);
        }

        @Override
        public void onBindViewHolder(BaseViewHolder holder, int position) {
//先判断是不是瀑布流，让footer独自占一行setFullSpan(true);
            if (isShowLoadMoreFooter && position == getItemCount() - 1) {
                if (holder.itemView.getLayoutParams() instanceof StaggeredGridLayoutManager.LayoutParams) {
                    StaggeredGridLayoutManager.LayoutParams params = (StaggeredGridLayoutManager.LayoutParams) holder.itemView.getLayoutParams();
                    params.setFullSpan(true);
                }


            }
            holder.onBindViewHolder(position);
        }

        @Override
        public int getItemCount() {
            return mDataList != null ? mDataList.size() + (isShowLoadMoreFooter ? 1 : 0) : 0;
        }


        @Override
        public int getItemViewType(int position) {
            if (isShowLoadMoreFooter && position == getItemCount() - 1) {
                return VIE_TYPE_LOAD_MORE_FOOTER;
            }
            return getItemType(position);
        }


        public void showLoadMoreFooter(boolean isShow) {
            this.isShowLoadMoreFooter = isShow;
            if (isShow) {
                notifyItemInserted(getItemCount());
            } else {
                notifyItemRemoved(getItemCount());
            }
        }

        public boolean isFooterView(int position) {
            return isShowLoadMoreFooter && position == getItemCount() - 1;
        }

        private class LoadMoreFooterViewHolder extends BaseViewHolder {
            public LoadMoreFooterViewHolder(View view) {
                super(view);
            }

            @Override
            public void onBindViewHolder(int position) {

            }
        }
    }

    protected int getItemType(int position) {
        return 0;
    }

    protected abstract BaseViewHolder getViewHolder(ViewGroup parent, int viewType);

}

对于GridLayoutManager中footer的处理

 FooterSpanSizeLookup lookup = new FooterSpanSizeLookup(adapter, getSpanCount());//getCount先取到设置的值
        setSpanSizeLookup(lookup);


public class FooterSpanSizeLookup extends GridLayoutManager.SpanSizeLookup {
    private BaseListActivity.BaseListAdapter adapter;
    private int spanCount;

    public FooterSpanSizeLookup(BaseListActivity.BaseListAdapter adapter, int spanCount) {
        this.adapter = adapter;
        this.spanCount = spanCount;
    }
//如果是footer，假设getCount是3，那么一个footer占3个位置，所以独自显示一行
//如果不是footer，默认是1
    @Override
    public int getSpanSize(int position) {
        if (adapter.isFooterView(position)) {
            return spanCount;
        }
        return 1;
    }
}

public class MyStaggeredGridLayoutManager extends StaggeredGridLayoutManager implements ILayoutManager {
    public MyStaggeredGridLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    public MyStaggeredGridLayoutManager(int spanCount, int orientation) {
        super(spanCount, orientation);
    }

    //判断最后一个
    //还要判断是否独占一行
    @Override
    public int findLastVisiblePosition() {
        int[] positions = null;
        positions = findLastVisibleItemPositions(positions);
        return positions[0];
    }

    @Override
    public RecyclerView.LayoutManager getLayoutManager() {
        return this;
    }

    @Override
    public void setUpAdapter(BaseListActivity.BaseListAdapter adapter) {

    }


}