如果要实现以下效果，你首先会想到怎么做呢？

GridLayoutManager gridLayoutManager = new GridLayoutManager(this, 3);
gridLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
            @Override
            public int getSpanSize(int position) {
                if(customAdapter.getItemCount() - 1 == position){
                    return 2;
                }else{
                    return 1;
                }
            }
});
mRecyclerview.setLayoutManager(gridLayoutManager);

• GridLayoutManager传入spanCount为3
• 最后一个Item占据两个span，其他占据一个span