将来自多个 firebase 目录的所有帖子显示到 recyclerView

Question

我正在研究关于课堂公告的论文，但我陷入了其中。

在我的数据库中，我决定将 post 个不同的用户归入几个类别。

Categories

Categories displaying posts

所以我已经成功地显示了一个类别（Class 公告）下的所有 post。

Classroom Announcements

private RecyclerView postList;

private DatabaseReference database;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    addPost = findViewById(R.id.btnAddPost);

    database = FirebaseDatabase.getInstance().getReference().child("St Isidore of Seville")
            .child("Posts").child("Classroom Announcements");

    postList = findViewById(R.id.postList);

    postList.setLayoutManager(new LinearLayoutManager(this));

}

 @Override
protected void onStart() {
    super.onStart();

    FirebaseRecyclerOptions<Post> options= new FirebaseRecyclerOptions.Builder<Post>()
            .setQuery(database, Post.class).build();

    firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<Post, PostViewHolder>(options) {
        @Override
        public PostViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.post_row, parent, false);

            return new PostViewHolder(view);
        }

        @Override
        protected void onBindViewHolder(@NonNull PostViewHolder holder, int position, @NonNull Post model) {
            holder.setTitle(model.getTitle());
            holder.setMessage(model.getMessage());
            holder.setDateCreated(model.getDateCreated());
        }
    };

    postList.setAdapter(firebaseRecyclerAdapter);

    firebaseRecyclerAdapter.startListening();
}

问题是只有 "Classroom Announcements" 下的公告是唯一可以显示的 post。如何显示所有公告，例如 "Bills"、"Homeworks"、"Others" 等...

我可以使用类似

的东西吗

database = FirebaseDatabase.getInstance().getReference().child("St Isidore of Seville")
            .child("Posts");

或者尽快将数据库中的每个类别都放入一个 FirebaseRecyclerAdapter 中，以便我可以使用它们的日期在顶部显示最近的 post？

Answer 1

您需要使用getChildren()两次，所以请使用以下代码：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference postsRef = rootRef.child("St Isidore of Seville").child("Posts");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            for(DataSnapshot child : ds.getChildren()) {
                Post model = child.getValue(Post.class);
                Log.d("TAG", model.getTitle() + " / " + model.getMessage() + " / " + model.getDateCreated());
            }
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        Log.d("TAG", databaseError.getMessage()); //Don't ignore potential errors!
    }
};
postsRef.addListenerForSingleValueEvent(eventListener);

将来自多个 firebase 目录的所有帖子显示到 recyclerView

Display all posts from multiple firebase directories into recyclerView

android

firebase

firebase-realtime-database

firebaseui