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？
Posted
技术标签:
【中文标题】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？【英文标题】：How to retrieve child from Firebase Database with a randomkey into recycler view in Android? 【发布时间】：2021-11-03 11:29:42 【问题描述】：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;
【问题讨论】：
如果您遇到问题，最好在发布问题时创建MCVE。您为此问题发布了近 400（四百）行行代码。人们需要解析和尝试在线调试的内容很多。请编辑您的问题并隔离问题，这样可以增加获得帮助的机会。 好的，谢谢您的建议 请修剪您的代码，以便更容易找到您的问题。请按照以下指南创建minimal reproducible example。 【参考方案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。
【讨论】：
嘿约翰。我可以帮助您了解其他信息吗？如果您认为我的回答对您有所帮助，请考虑通过单击左侧投票箭头下方的复选标记（✔️）来接受它。应将颜色更改为绿色。我真的很感激。谢谢！【参考方案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");
【讨论】：
非常感谢您的回答，我会这样做的。以上是关于如何使用随机键从 Firebase 数据库中检索子项到 Android 的回收站视图中？的主要内容，如果未能解决你的问题，请参考以下文章
如何在不从参考节点获取所有数据的情况下获取 Firebase 数据库中的随机键？