如何使用recyclerview:1.2.0-alpha02实现RecyclerView滚动位置自动保存与恢复

第一步：升级RecyclerView依赖 #

直接使用最新稳定版即可，无需使用老旧的alpha测试版，在模块级build.gradle的dependencies块中添加：

implementation "androidx.recyclerview:recyclerview:1.3.2"

该版本默认启用滚动位置自动恢复能力，支持StaggeredGridLayoutManager等官方布局管理器。

第二步：核心前提条件 #

你需要先确认布局文件中的RecyclerView已设置唯一的android:id，View的状态保存依赖id实现，无id的控件无法自动保存状态。

第三步：修复现有代码逻辑问题 #

3.1 修改PostAdapter_Home.java #

• 移除mUploads的static修饰符，避免多实例数据共享异常
• 开启稳定ID，重写getItemId方法，用每个Upload的唯一key作为item标识
  修改后代码如下：

public class PostAdapter_Home extends RecyclerView.Adapter<PostAdapter_Home.PostViewHolder> {
    // 移除static修饰
    private List<Upload> mUploads;
    private Context mcontext;

    public PostAdapter_Home(Context context, List<Upload> uploads) {
        mUploads = uploads;
        mcontext = context;
        // 开启稳定ID
        setHasStableIds(true);
    }

    // 新增重写getItemId方法
    @Override
    public long getItemId(int position) {
        // 用每个Upload的唯一key生成id，保证唯一性
        return mUploads.get(position).getmKey().hashCode();
    }

    @NonNull
    @Override
    public PostViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(mcontext).inflate(R.layout.ex_home, parent, false);
        return new PostViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull PostViewHolder holder, int position) {
        Shimmer shimmer = new Shimmer.ColorHighlightBuilder()
                .setBaseColor(Color.parseColor("#F3F3F3"))
                .setBaseAlpha(1)
                .setHighlightColor(Color.parseColor("#E7E7E7"))
                .setHighlightAlpha(1)
                .setDropoff(50)
                .build();
        ShimmerDrawable shimmerDrawable = new ShimmerDrawable();
        shimmerDrawable.setShimmer(shimmer);
        Upload uploadCurrent = mUploads.get(position);
        Glide.with(mcontext)
                .load(uploadCurrent.getmImageUrl())
                .diskCacheStrategy(DiskCacheStrategy.AUTOMATIC)
                .placeholder(shimmerDrawable)
                .centerCrop()
                .fitCenter()
                .into(holder.imageView);
    }

    @Override
    public int getItemCount() {
        return mUploads.size();
    }

    public static class PostViewHolder extends RecyclerView.ViewHolder {
        private final ShapeableImageView imageView;
        public PostViewHolder(@NonNull View itemView) {
            super(itemView);
            imageView = itemView.findViewById(R.id.imagePostHome);
        }
    }
}

3.2 修改Home_Fragment.java #

• 调整初始化顺序：先初始化数据列表、Adapter、RecyclerView配置，再加载数据
• 移除手动调用scrollToPosition的代码，交由系统自动恢复
• 优化数据加载逻辑，避免数据更新重置滚动状态
  修改后核心代码如下：

private final String KEY_RECYCLER_STATE = "recycler_state";
public List<Upload> mUploads;
PostAdapter_Home postsAdapter;
ShimmerFrameLayout shimmerFrameLayout;
private RecyclerView postRecyclerView;
private int pastVisibleItems, visibleItemCount, totalItemCount;

@SuppressLint("SourceLockedOrientationActivity")
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_home, container, false);
    requireActivity().setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
    MaterialToolbar materialToolbar = view.findViewById(R.id.toolbar);
    materialToolbar.setOnMenuItemClickListener(toolbarItemClickListener);
    postRecyclerView = view.findViewById(R.id.recyclerViewHome);
    shimmerFrameLayout = view.findViewById(R.id.shimmerEffect);

    StaggeredGridLayoutManager staggeredGridLayoutManager = new StaggeredGridLayoutManager(1, StaggeredGridLayoutManager.VERTICAL);
    postRecyclerView.setLayoutManager(staggeredGridLayoutManager);

    // 先初始化数据列表和Adapter
    mUploads = new ArrayList<>();
    postsAdapter = new PostAdapter_Home(getContext(), mUploads);
    postRecyclerView.setAdapter(postsAdapter);

    // 再启动数据加载
    shimmerFrameLayout.startShimmer();
    getData();

    return view;
}

private void getData() {
    databaseReference.addValueEventListener(new ValueEventListener() {
        @SuppressLint("NotifyDataSetChanged")
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            List<Upload> newUploads = new ArrayList<>();
            if (snapshot.exists()) {
                for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
                    Upload upload = dataSnapshot.getValue(Upload.class);
                    assert upload != null;
                    upload.setmKey(dataSnapshot.getKey());
                    newUploads.add(upload);
                }
            }
            mUploads.clear();
            mUploads.addAll(newUploads);
            postsAdapter.notifyDataSetChanged();

            shimmerFrameLayout.stopShimmer();
            shimmerFrameLayout.setVisibility(View.GONE);
            postRecyclerView.setVisibility(View.VISIBLE);
        }

        @Override
        public void onCancelled(@NonNull DatabaseError error) {
            // 处理异常逻辑
        }
    });
}

可选优化（推荐） #

如果想进一步提升性能、避免全局刷新带来的闪烁问题，可以用DiffUtil替代notifyDataSetChanged做局部更新，滚动位置恢复的稳定性会更高。

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