如何将分页请求发送到firebase以实现无限滚动的recyclerview

Question

我正在尝试在我的应用程序中包含我想要的分页，例如在我的 Firebase 中，我有 500 个要在回收站视图中显示的图像我想要的是在回收站视图中加载前 10 或 15 个图像在开始时，当用户到达最后一项（图像）的末尾时，它会加载接下来的 10 张图像（就像 Instagram 或 facebook 一样）

注意：- 如果有人想要更多参考我的代码，请告诉我我会 更新我的问题

这是我的代码

Home_Fragment.java

private boolean loading = true;
    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);
//        this is for one item per scroll
//        SnapHelper snapHelper = new PagerSnapHelper();
//        snapHelper.attachToRecyclerView(verticalRecyclerView);
        postRecyclerView.setAdapter(postsAdapter);
//        listState = savedInstanceState.getParcelable("ListState");

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


        postRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {

                visibleItemCount = staggeredGridLayoutManager.getChildCount();
                totalItemCount = staggeredGridLayoutManager.getItemCount();
                int[] firstVisibleItems = null;
                firstVisibleItems = staggeredGridLayoutManager.findFirstVisibleItemPositions(firstVisibleItems);
                if (firstVisibleItems != null && firstVisibleItems.length > 0) {
                    pastVisibleItems = firstVisibleItems[0];
                }

                if (loading) {
                    if ((visibleItemCount + pastVisibleItems) >= totalItemCount) {
                        loading = false;
                        getData();
                        Log.d("tag", "LOAD NEXT ITEM");
                    }
                }
            }
        });
//        setupFirebaseAuth();
        shimmerFrameLayout.startShimmer();
        mUploads = new ArrayList<>();
        postsAdapter = new PostAdapter_Home(getContext(), mUploads);
        postRecyclerView.setAdapter(postsAdapter);
        postRecyclerView.scrollToPosition(Home_Fragment.saved_position);
        return view;
    }


    private void getData() {
        databaseReference.addValueEventListener(new ValueEventListener() {
            @SuppressLint("NotifyDataSetChanged")
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                if (snapshot.exists()) {
                    shimmerFrameLayout.stopShimmer();
                    shimmerFrameLayout.setVisibility(View.GONE);
                    postRecyclerView.setVisibility(View.VISIBLE);
                    mUploads.clear();
                    for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
                        Upload upload = dataSnapshot.getValue(Upload.class);
                        assert upload != null;
                        upload.setmKey(dataSnapshot.getKey());
                        mUploads.add(upload);


                    }

                }
                postsAdapter.setUploads(mUploads);

                //notify the adapter
                postsAdapter.notifyDataSetChanged();
                loading = true;
            }

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

PostAdapter_Home.java // 适配器类

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

    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.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);

//        holder.imageView.setOnClickListener(view -> changeScaleType(holder, position));

    }


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

    public void setUploads(List<Upload> uploads){
        mUploads=uploads;
    }
    public static class PostViewHolder extends RecyclerView.ViewHolder {

        private final ShapeableImageView imageView;

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

        }


    }
}

更新 // 根据评论部分的要求添加了 Upload.java 文件代码

上传.java

package com.example.myappnotfinal.AdaptersAndMore;

import com.google.firebase.database.Exclude;

public class Upload {
    private String mImageUrl;
    private String mKey;
    private String mUserName;
    private String mComment;

    public Upload() {

    }

    public Upload(String imageUrl) {
        mImageUrl = imageUrl;
    }

    public String getmUserName() {
        return mUserName;
    }

    public void setmUserName(String mUserName) {
        this.mUserName = mUserName;
    }

    public String getmComment() {
        return mComment;
    }

    public void setmComment(String mComment) {
        this.mComment = mComment;
    }

    public String getmImageUrl() {
        return mImageUrl;
    }

    public void setmImageUrl(String mImageUrl) {
        this.mImageUrl = mImageUrl;
    }

    @Exclude
    public String getmKey() {
        return mKey;
    }

    @Exclude
    public void setmKey(String Key) {
        this.mKey = Key;
    }
}

Answer 1

首先，您应该将获取数据的逻辑与 UI 分开。然后你的滚动控制器（RecyclerView）应该控制应该调用哪些图像来下载（所以当它加载时它应该要求第一批图像，当滚动发生时 - 要求另一批，等等）。下载和缓存图片并不是一件容易的事，这就是为什么我们在 Android 世界中有Glide 和Coil。

作为旁注，请查看https://developer.android.com/topic/libraries/architecture/paging/v3-paged-data 和https://developer.android.com/topic/libraries/architecture/paging。

请检查您要添加到 mUploads 列表中的内容，因为每次添加项目时，您都会预先清除列表 mUploads.clear();，这可能不是您想要的。

一些注意事项：

• 不要让它静态public static List<Upload> mUploads;
• 不需要存储mcontext，上下文已经存在
• 从不必要的东西中剔除问题（例如，删除微光，修复问题，修复后添加微光）

Answer 2

这里需要setLimit进行分页处理。

这里是示例：

private void getUsers(String nodeId) {
Query query;

if (nodeId == null)
    query = FirebaseDatabase.getInstance().getReference()
            .child(Consts.FIREBASE_DATABASE_LOCATION_USERS)
            .orderByKey()
            .limitToFirst(mPostsPerPage);
else
    query = FirebaseDatabase.getInstance().getReference()
            .child(Consts.FIREBASE_DATABASE_LOCATION_USERS)
            .orderByKey()
            .startAt(nodeId)
            .limitToFirst(mPostsPerPage);

query.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        UserModel user;
        List<UserModel> userModels = new ArrayList<>();
        for (DataSnapshot userSnapshot : dataSnapshot.getChildren()) {
            userModels.add(userSnapshot.getValue(UserModel.class));
        }

        mAdapter.addAll(userModels);
        mIsLoading = false;
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        mIsLoading = false;
    }
  });
}

所以这里你需要每次发送最后一个节点 id 来获取新列表。得到响应后，只需将您的数据添加到ArrayList 或您使用的任何逻辑。然后像这样更新 RecyclerView：

 blogRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState) {
            super.onScrollStateChanged(recyclerView, newState);
            if (newState == AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL) {
                isScrolling = true;
            }
        }

        @Override
        public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            currentItems = manager.getChildCount();
            totalItems = manager.getItemCount();
            scrollOutItems = manager.findFirstVisibleItemPosition();

            if (isScrolling && (currentItems + scrollOutItems == totalItems) && nextPage != null) {
                isScrolling = false;
                progressBar.setVisibility(View.VISIBLE);
                 getUsers(mlastNodeId);//here your last id will be
            }
        }
    });
}