2个RecyclerView 左右布局联动

为啥要联动？快速定位方便选择，常见有新闻啊，外卖菜单啊。

效果图片

右边的数据源格式

[
  {
   name:'分类1'
   isType: true
  },
  {
   name:'商品1'
   isType: false
  },
  {
   name:'商品2'
   isType: false
  },
  {
   name:'商品3'
   isType: false
  },
  {
   name:'分类2'
   isType: true
  },
  {
   name:'商品4'
   isType: false
  },
  {
   name:'商品5'
   isType: false
  },
...
]

左边RecyclerView 点击的监听

        categoryAdapter.setListener(new HomeCategoryAdapter.OnItemClickListener() {
            @Override
            public void clicked(LzFoodType foodType, int position) {
                categoryAdapter.setSelectedPos(position);
                clickMenu = true;

                int p = 0;
                for (int i=0; i < foodAdapter.list.size(); i++) {
                    LzFood fo = foodAdapter.list.get(i);
                    if (fo.getName().equals(foodType.getName())) {
                        p = i;
                        break;
                    }
                }

                int first = layoutManagerFood.findFirstVisibleItemPosition();
                int last = layoutManagerFood.findLastVisibleItemPosition();

                if (p <= first) {
                    recyclerList.smoothScrollToPosition(p);
                    Log.d("lxf", ">>>>> 1 <<<<<<<");

                } else if (p <= last) {
                    int top = recyclerList.getChildAt(p - first).getTop();
                    recyclerList.smoothScrollBy(0, top);
                    Log.d("lxf", ">>>>> 2 <<<<<<<");

                } else {
                    recyclerList.scrollToPosition(p);
                    new Handler().postDelayed(new Runnable() {
                        @Override
                        public void run() {
                           int first2 = layoutManagerFood.findFirstVisibleItemPosition();
                           int last2 = layoutManagerFood.findLastVisibleItemPosition();
                           if (recyclerList.getChildAt(last2-first2) != null) {
                               int top = recyclerList.getChildAt(last2 - first2).getTop();
                               recyclerList.smoothScrollBy(0, top);
                           }
                        }
                    }, 50);

                    Log.d("lxf", ">>>>> 3 <<<<<<<");
                }

            }
        });

右边列表 滚动监听

        recyclerList.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);

                if (newState == RecyclerView.SCROLL_STATE_DRAGGING) {
                    clickMenu = false;
                }
            }

            @Override
            public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);

                if (!clickMenu) {
                    int first = layoutManagerFood.findFirstVisibleItemPosition();
                    changeMenuSelected(first);
                }
            }
        });

右边列表滚动时，对左边修改

通过右边列表显示的第一个可见item，来改变左边菜单
使用倒序遍历，总能找一个 isType 为 true 的 model

    private void changeMenuSelected(int first){
        int now = first;
        LzFood food = null;
        for (int i=first; i>=0; i--) {
            LzFood f = foodAdapter.list.get(i);
            if (f.isType){
                now = i;
                food = f;
                break;
            }
        }
        if (food == null) return;
        for (int i=0; i<categoryAdapter.list.size(); i++) {
            LzFoodType ft = categoryAdapter.list.get(i);
            if (ft.getName().equals(food.getName())){
                now = i;
                break;
            }
        }

       //notifyDataSetChanged() 在set中
        categoryAdapter.setSelectedPos(now);
        recyclerMenu.smoothScrollToPosition(now);
    }
    

联动标记

标记是用户手动滚动列表，还是点击左边菜单滚动右边

  private boolean clickMenu = false;

关于如何设置组头悬浮

由于未使用 ItemDecoration，所以可以使用 组头 的布局相对 recyclerView进行布局，然后修改内容即可。。。。