如何使用随机键从 Firebase 数据库中检索子项到 Android 的回收站视图中？

Question

我实际上是 Android 编程新手，但我想使用随机键从 Firebase 数据库中检索一个子项（评论）到 RecyclerView。我已经编写了一些代码，但是当我启动应用程序时，孩子（评论）没有显示它也没有给我任何错误。请帮忙，提前谢谢。

我的 Java 代码：

private String commentsID = "";
private ImageView imageView, share, commentimage, profileimage, newslikeimage, send;
private TextView heading, description, newsdate, newstime, newscounter, sharecounter, newcommentcounter, profilename;
private String commentsend, commentcurrentusers, newcommentcurrentusers;
private EditText writecomment;
private DatabaseReference commentRef;
private RecyclerView.LayoutManager layoutManager;
private RecyclerView recyclerView;

private String saveCurrentDate, saveCurrentTime, commentRandomKey;

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

    commentRef = FirebaseDatabase.getInstance().getReference().child("Comments");
    
    recyclerView = findViewById(R.id.commentrecycler);
    recyclerView.setHasFixedSize(true);
    layoutManager = new LinearLayoutManager(this);
    recyclerView.setLayoutManager(layoutManager);
    recyclerView.setLayoutManager(layoutManager);

    commentsID = getIntent().getStringExtra("comments");

    imageView = findViewById(R.id. newsimage);
    heading = findViewById(R.id. newsname);
    description = findViewById(R.id. newsdescription);
    newsdate = findViewById(R.id. newdate);
    newstime = findViewById(R.id. newtime);
    newscounter = findViewById(R.id. newcounter);
    sharecounter = findViewById(R.id. sharecounter);
    commentimage = findViewById(R.id. commentimage);
    newcommentcounter = findViewById(R.id. newcommentcounter);

    newslikeimage = findViewById(R.id. newslike);
    share = findViewById(R.id. share);
    profileimage = findViewById(R.id. profileimage);
    profilename = findViewById(R.id. profilename);
    send = findViewById(R.id. send);
    writecomment = findViewById(R.id. sendcomment);
}

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

    FirebaseUser currentuser = FirebaseAuth.getInstance().getCurrentUser();
    newcommentcurrentusers = currentuser.getUid();

    getCommentsDetails(commentsID);


    send.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v)
        {
            commentsend = writecomment.getText().toString();

            if (TextUtils.isEmpty(commentsend))
            {
                Toast.makeText(CommentActivity.this, "Please type your comment", Toast.LENGTH_SHORT).show();
            }
            else
            {
                sendingCommentsToFirebase();
            }

        }
    });

    FirebaseRecyclerOptions<Comment> options =
            new FirebaseRecyclerOptions.Builder<Comment>()
                    .setQuery(commentRef, Comment.class)
                    .build();

    FirebaseRecyclerAdapter<Comment, CommentsViewHolder> adapter =
            new FirebaseRecyclerAdapter<Comment, CommentsViewHolder>(options) {
                @Override
                protected void onBindViewHolder(@NonNull CommentsViewHolder holder, int position, @NonNull Comment model) {

                    holder.comment.setText(model.getComments());
                }

                @NonNull
                @Override
                public CommentsViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
                    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.comment_item_layout, parent, false);
                    CommentsViewHolder holder = new CommentsViewHolder(view);
                    return holder;
                }
            };
    recyclerView.setAdapter(adapter);
    adapter.startListening();
}

private void sendingCommentsToFirebase()
{
    FirebaseUser currentuser = FirebaseAuth.getInstance().getCurrentUser();
    commentcurrentusers = currentuser.getUid();

    Calendar calendar = Calendar.getInstance();

    SimpleDateFormat currentDate = new SimpleDateFormat("MMM dd, yyyy");
    saveCurrentDate = currentDate.format(calendar.getTime());

    SimpleDateFormat currentTime = new SimpleDateFormat("HH:mm:ss a");
    saveCurrentTime = currentTime.format(calendar.getTime());

    commentRandomKey = saveCurrentDate + saveCurrentTime;

    HashMap<String, Object> commentMap = new HashMap<>();
    commentMap.put("comments", commentsend);
    commentMap.put("userID", commentcurrentusers);
    commentMap.put("newspid", commentRandomKey);

    commentRef.child(commentsID).push().setValue(commentMap).addOnCompleteListener(new OnCompleteListener<Void>() {
        @Override
        public void onComplete(@NonNull  Task<Void> task)
        {
            if (task.isSuccessful())
            {
                Toast.makeText(CommentActivity.this, "Comments added", Toast.LENGTH_SHORT).show();

            }
        }
    });
}

private void getCommentsDetails(String commentsID) {
    DatabaseReference newsRef = FirebaseDatabase.getInstance().getReference().child("News");

    newsRef.child(commentsID).addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            if (snapshot.exists()) {
                News news = snapshot.getValue(News.class);

                heading.setText(news.getHeading());
                description.setText(news.getDecription());
                profilename.setText(news.getUsername());
                newsdate.setText(news.getDate());
                newstime.setText(news.getTime());
                newscounter.setText(news.getLikes());
                sharecounter.setText(news.getShare());
                newcommentcounter.setText(news.getComment());

                Picasso.get().load(news.getProfileimage()).into(profileimage);
                Picasso.get().load(news.getImage()).into(imageView);
            }
        }

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

        }
    });

这是我的视图持有者

public class CommentActivity extends AppCompatActivity
{
    private String commentsID = "";
    private ImageView imageView, share, commentimage, profileimage, newslikeimage, send;
    private TextView heading, description, newsdate, newstime, newscounter, sharecounter, newcommentcounter, profilename;
    private String commentsend, commentcurrentusers, newcommentcurrentusers;
    private EditText writecomment;
    private DatabaseReference commentRef;
    private RecyclerView.LayoutManager layoutManager;
    private RecyclerView recyclerView;

    private String saveCurrentDate, saveCurrentTime, commentRandomKey;

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

        commentRef = FirebaseDatabase.getInstance().getReference().child("Comments");
        
        recyclerView = findViewById(R.id.commentrecycler);
        recyclerView.setHasFixedSize(true);
        layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setLayoutManager(layoutManager);

        commentsID = getIntent().getStringExtra("comments");

        imageView = findViewById(R.id. newsimage);
        heading = findViewById(R.id. newsname);
        description = findViewById(R.id. newsdescription);
        newsdate = findViewById(R.id. newdate);
        newstime = findViewById(R.id. newtime);
        newscounter = findViewById(R.id. newcounter);
        sharecounter = findViewById(R.id. sharecounter);
        commentimage = findViewById(R.id. commentimage);
        newcommentcounter = findViewById(R.id. newcommentcounter);

        newslikeimage = findViewById(R.id. newslike);
        share = findViewById(R.id. share);
        profileimage = findViewById(R.id. profileimage);
        profilename = findViewById(R.id. profilename);
        send = findViewById(R.id. send);
        writecomment = findViewById(R.id. sendcomment);
    }

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

        FirebaseUser currentuser = FirebaseAuth.getInstance().getCurrentUser();
        newcommentcurrentusers = currentuser.getUid();

        getCommentsDetails(commentsID);

        send.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {
                commentsend = writecomment.getText().toString();

                if (TextUtils.isEmpty(commentsend))
                {
                    Toast.makeText(CommentActivity.this, "Please type your comment", Toast.LENGTH_SHORT).show();
                }
                else
                {
                    sendingCommentsToFirebase();
                }

            }
        });

        FirebaseRecyclerOptions<Comment> options =
                new FirebaseRecyclerOptions.Builder<Comment>()
                        .setQuery(commentRef, Comment.class)
                        .build();

        FirebaseRecyclerAdapter<Comment, CommentsViewHolder> adapter =
                new FirebaseRecyclerAdapter<Comment, CommentsViewHolder>(options) {
                    @Override
                    protected void onBindViewHolder(@NonNull CommentsViewHolder holder, int position, @NonNull Comment model) {

                        holder.comment.setText(model.getComments());
                    }

                    @NonNull
                    @Override
                    public CommentsViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
                        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.comment_item_layout, parent, false);
                        CommentsViewHolder holder = new CommentsViewHolder(view);
                        return holder;
                    }
                };
        recyclerView.setAdapter(adapter);
        adapter.startListening();
    }

    private void sendingCommentsToFirebase()
    {
        FirebaseUser currentuser = FirebaseAuth.getInstance().getCurrentUser();
        commentcurrentusers = currentuser.getUid();

        Calendar calendar = Calendar.getInstance();

        SimpleDateFormat currentDate = new SimpleDateFormat("MMM dd, yyyy");
        saveCurrentDate = currentDate.format(calendar.getTime());

        SimpleDateFormat currentTime = new SimpleDateFormat("HH:mm:ss a");
        saveCurrentTime = currentTime.format(calendar.getTime());

        commentRandomKey = saveCurrentDate + saveCurrentTime;

        HashMap<String, Object> commentMap = new HashMap<>();
        commentMap.put("comments", commentsend);
        commentMap.put("userID", commentcurrentusers);
        commentMap.put("newspid", commentRandomKey);

        commentRef.child(commentsID).push().setValue(commentMap).addOnCompleteListener(new OnCompleteListener<Void>() {
            @Override
            public void onComplete(@NonNull  Task<Void> task)
            {
                if (task.isSuccessful())
                {
                    Toast.makeText(CommentActivity.this, "Comments added", Toast.LENGTH_SHORT).show();

                }

            }
        });

    }

    private void getCommentsDetails(String commentsID) {
        DatabaseReference newsRef = FirebaseDatabase.getInstance().getReference().child("News");

        newsRef.child(commentsID).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                if (snapshot.exists()) {
                    News news = snapshot.getValue(News.class);

                    heading.setText(news.getHeading());
                    description.setText(news.getDecription());
                    profilename.setText(news.getUsername());
                    newsdate.setText(news.getDate());
                    newstime.setText(news.getTime());
                    newscounter.setText(news.getLikes());
                    sharecounter.setText(news.getShare());
                    newcommentcounter.setText(news.getComment());

                    Picasso.get().load(news.getProfileimage()).into(profileimage);
                    Picasso.get().load(news.getImage()).into(imageView);
                }
            }

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

            }
        });
    }
}

这是我的班级：

public class Comment
{
    private String comments, newspid, userID;

    private Comment()
    {

    }

    public Comment(String comments, String newspid, String userID) {
        this.comments = comments;
        this.newspid = newspid;
        this.userID = userID;
    }

    public String getComments() {
        return comments;
    }

    public void setComments(String comments) {
        this.comments = comments;
    }

    public String getNewspid() {
        return newspid;
    }

    public void setNewspid(String newspid) {
        this.newspid = newspid;
    }

    public String getUserID() {
        return userID;
    }

    public void setUserID(String userID) {
        this.userID = userID;
    }
}

Answer 1

由于以下参考，您很可能在 RecyclerView 中没有得到任何东西：

commentRef = FirebaseDatabase.getInstance().getReference().child("Comments");

在您的“评论”节点下，没有“评论”类型的对象，只有字符串键（2021 年 9 月 3 日...）。为了能够读取您感兴趣的对象，您应该在数据库中删除该额外级别，因为我看到您已经将“日期”存储到 newspid 属性中，因此不需要它。所以你的架构应该是这样的：

Firebase-root
  |
  --- Comments
        |
        --- $commentId
               |
               --- comments: "This is my comment"
               |
               --- newspid: "Sept 06..."
               |
               --- userID: "D31D..."

而且您的代码可以保持不变。

Answer 2

Alex 在他的回答中提出了问题的要点：FirebaseUI 中的适配器只能显示数据库中节点的平面列表，而您有两个嵌套级别。

您可以按照 Alex 的建议进行操作，并将所有 cmets 存储在一个平面列表中，或者您可以从当前数据结构中显示某一天的 cmets：

commentRef = FirebaseDatabase.getInstance().getReference()
                             .child("Comments").child("Sep 03, 202100:21:52 AM");