Android多头部粘性RecyclerView实现求助：头部无法粘滞

首先，咱们先梳理下你当前实现里的两个核心问题：

一、修复头部识别逻辑的错误 #

你现在的isPositionHeader方法只把position == 0的item当成头部，但你的数据源里每个分组都有自己的头部（通过isHeader=true标记），这就导致后面的头部都被当成普通item处理了。

把Adapter里的头部判断逻辑改成根据ItemObject的属性来判断：

private boolean isPositionHeader(int position) {
    // 替换原来的position==0，用数据里的isHeader标记判断
    return itemObjects.get(position).isHeader();
}

同时注意你getDataSource里的小错误：你把list1加了两次，改成只加一次就行：

private List <ItemObject> getDataSource(){
    List<ItemObject> list1 = new ArrayList <ItemObject>();
    list1.add(new ItemObject("First Header",true));
    list1.add(new ItemObject("This is the item content in the first position"));
    list1.add(new ItemObject("This is the item content in the second position"));

    List <ItemObject> list2 = new ArrayList <ItemObject>();
    list2.add(new ItemObject("Second Header",true));
    list2.add(new ItemObject("This is the item content in the first position"));
    list2.add(new ItemObject("This is the item content in the second position"));

    List <ItemObject> list3 = new ArrayList <ItemObject>();
    list3.add(new ItemObject("Third Header",true));
    list3.add(new ItemObject("This is the item content in the first position"));
    list3.add(new ItemObject("This is the item content in the second position"));

    List <ItemObject> finalList = new ArrayList <ItemObject>();
    finalList.addAll(list1);
    finalList.addAll(list2);
    finalList.addAll(list3);
    return finalList;
}

二、实现粘性头部功能 #

原生的LinearLayoutManager本身不支持粘性头部，咱们可以通过自定义RecyclerView.ItemDecoration来实现——这个方案比自定义LayoutManager简单很多，适合新手。

1. 自定义StickyHeaderDecoration类 #

public class StickyHeaderDecoration extends RecyclerView.ItemDecoration {
    private RecyclerViewAdapter adapter;

    public StickyHeaderDecoration(RecyclerViewAdapter adapter) {
        this.adapter = adapter;
    }

    @Override
    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDrawOver(c, parent, state);

        // 获取当前可见的第一个item位置
        int firstVisiblePos = ((LinearLayoutManager) parent.getLayoutManager()).findFirstVisibleItemPosition();
        if (firstVisiblePos == RecyclerView.NO_POSITION) return;

        // 找到当前需要悬浮的头部位置：如果当前可见item不是头部，就找它前面最近的头部
        int headerPos = firstVisiblePos;
        if (!adapter.isPositionHeader(firstVisiblePos)) {
            headerPos = findPrevHeaderPos(firstVisiblePos);
            if (headerPos == RecyclerView.NO_POSITION) return;
        }

        // 创建并绑定头部View
        RecyclerView.ViewHolder headerHolder = adapter.createViewHolder(parent, RecyclerViewAdapter.TYPE_HEADER);
        adapter.onBindViewHolder(headerHolder, headerPos);
        View headerView = headerHolder.itemView;

        // 测量并布局头部View
        int widthSpec = View.MeasureSpec.makeMeasureSpec(parent.getWidth(), View.MeasureSpec.EXACTLY);
        int heightSpec = View.MeasureSpec.makeMeasureSpec(View.MeasureSpec.UNSPECIFIED, View.MeasureSpec.UNSPECIFIED);
        headerView.measure(widthSpec, heightSpec);
        headerView.layout(0, 0, headerView.getMeasuredWidth(), headerView.getMeasuredHeight());

        // 计算头部绘制的Y坐标：处理下一个头部上来时的推挤效果
        int drawTop = parent.getPaddingTop();
        int nextHeaderPos = findNextHeaderPos(headerPos);
        if (nextHeaderPos != RecyclerView.NO_POSITION) {
            View nextHeaderView = parent.findViewHolderForAdapterPosition(nextHeaderPos).itemView;
            int offset = nextHeaderView.getTop() - headerView.getMeasuredHeight() - parent.getPaddingTop();
            if (offset < 0) {
                drawTop += offset;
            }
        }

        // 绘制悬浮头部
        c.save();
        c.translate(parent.getPaddingLeft(), drawTop);
        headerView.draw(c);
        c.restore();
    }

    // 找当前位置之前最近的头部
    private int findPrevHeaderPos(int currentPos) {
        for (int i = currentPos - 1; i >= 0; i--) {
            if (adapter.isPositionHeader(i)) return i;
        }
        return RecyclerView.NO_POSITION;
    }

    // 找当前头部之后的下一个头部
    private int findNextHeaderPos(int currentHeaderPos) {
        for (int i = currentHeaderPos + 1; i < adapter.getItemCount(); i++) {
            if (adapter.isPositionHeader(i)) return i;
        }
        return RecyclerView.NO_POSITION;
    }
}

2. 在MainActivity中添加Decoration #

修改你的RecyclerView初始化代码，加上这个粘性头部装饰：

recyclerView = findViewById(R.id.recyclerView);
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(MainActivity.this);
recyclerView.setLayoutManager(linearLayoutManager);
recyclerView.setHasFixedSize(true);
RecyclerViewAdapter adapter = new RecyclerViewAdapter(this , getDataSource());
// 新增：添加粘性头部Decoration
recyclerView.addItemDecoration(new StickyHeaderDecoration(adapter));
recyclerView.setAdapter(adapter);

最后说下你的初始实现思路 #

你的Adapter基础框架是对的（区分了头部和普通item），但核心问题有两个：一是头部识别逻辑错误，二是没意识到原生LayoutManager不支持粘性头部。现在修改后就能实现你要的多头部粘性效果了。

内容的提问来源于stack exchange，提问作者user11523459