android - 如何在 fragment 中保存和恢复recyclerview的位置

Question

这个问题在这里已经有了答案:





How to save RecyclerView's scroll position using RecyclerView.State?

(19 个回答)


6 个月前关闭。




你好我想在从一个 fragment 导航到另一个 fragment 时保存回收器 View 的位置，然后在返回到 fragment 时恢复滚动位置
笔记

I didn't try any method till now because I don't know where exactly Ihave to implement it in my Home_Fragmen.java or in PostAdapter_Home.java

现在，我如何在我的代码中实现这一点？
首页_Fragment.java

 public class Home_Fragment extends Fragment {
    private final DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("uploads");
    public List<Upload> mUploads;
    PostAdapter_Home postsAdapter;
    RecyclerView postRecyclerView;
    ShimmerFrameLayout shimmerFrameLayout;

    @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);
        postRecyclerView = view.findViewById(R.id.recyclerViewHome);
        shimmerFrameLayout = view.findViewById(R.id.shimmerEffect);
        SnapHelper snapHelper = new PagerSnapHelper();
        snapHelper.attachToRecyclerView(postRecyclerView);
        postRecyclerView.setLayoutManager(
                new StaggeredGridLayoutManager(1, StaggeredGridLayoutManager.VERTICAL)
        );

        getData();
        shimmerFrameLayout.startShimmer();
        mUploads = new ArrayList<>();
        postsAdapter = new PostAdapter_Home(getContext(), mUploads);
        postRecyclerView.setAdapter(postsAdapter);
        return view;
    }

    private void getData() {
        databaseReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                if (snapshot.exists()) {

                    postRecyclerView.setVisibility(View.VISIBLE);
                    shimmerFrameLayout.stopShimmer();
                    shimmerFrameLayout.setVisibility(View.GONE);
                    mUploads.clear();
                    for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
                        Upload upload = dataSnapshot.getValue(Upload.class);
                        assert upload != null;
                        upload.setmKey(dataSnapshot.getKey());
                        mUploads.add(upload);


                    }

                }

                //notify the adapter
                postsAdapter.notifyDataSetChanged();
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {
            }
        });
    }
}

PostAdapter_Home.java

public class PostAdapter_Home extends RecyclerView.Adapter<PostAdapter_Home.PostViewHolder> {
    public static List<Upload> mUploads;
    public Context mcontext;
    //    ShimmerFrameLayout shimmerFrameLayout;


    public PostAdapter_Home(Context context, List<Upload> uploads) {
        mUploads = uploads;
        mcontext = context;
    }


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

    }

    @Override
    public void onBindViewHolder(@NonNull PostViewHolder holder, int position) {
        Upload uploadCurrent = mUploads.get(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);
        Glide.with(mcontext)
                .load(uploadCurrent.getmImageUrl())
                .diskCacheStrategy(DiskCacheStrategy.DATA)
                .placeholder(shimmerDrawable)
                .into(holder.imageView);


    }

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

    public static class PostViewHolder extends RecyclerView.ViewHolder {
        ShapeableImageView imageView;

        public PostViewHolder(@NonNull View itemView) {
            super(itemView);
            imageView = itemView.findViewById(R.id.imagePostHome);
        }


        public void setOnItemClickListener(PostAdapter.OnItemClickListener listener) {

        }
    }
}

Answer 1

一种简单的解决方案是使用静态变量。

将以下作为属性添加到您的类:public static int saved_position = 0 (0 值必须是您的 recyclerView 位置的默认值)。

每当 recyclerView 值更改时，添加 Home_Fragment.saved_position = ... , 以保存变量中的实际位置。这行代码可以毫无问题地在任何文件上运行，因为静态变量是公共(public)的。

创建fragment时，将recyclerView位置设置为Home_Fragment.saved_position中保存的位置，这就是为什么您必须将默认值设置为初始值的原因。

如果由于某种原因recyclerView中的元素数量发生了变化，记得改变Home_Fragment.saved_position的值。到默认值。