java - Android 自定义 ListView 仅显示 Firebase 数据库中的一项

Question

这是一个 Firebase 聊天应用程序，聊天窗口或 ListView 是一个 Activity 的 fragment 这就是 Firebase JSON 树的样子，

我制作了三个类 FirebaseHelper、ChatListAdapter 和 ChatListManager

FirebaseHelper.java

public class FirebaseHelper {
    DatabaseReference db;
    Boolean saved;
    ArrayList<ChatListManager> chatListArr = new ArrayList<>();


    public FirebaseHelper(DatabaseReference db) {
        this.db = db;
    }

    public boolean sendChat(String uname, String message) {
        if (chatListArr == null) {
            saved = false;
        } else {
            try {
                Map<String, Object> keyMap = new HashMap<String, Object>();
                String tempKey = db.push().getKey();
                db.updateChildren(keyMap);
                DatabaseReference chat;
                chat = db.child(tempKey);
                Map<String, String> chats = new HashMap<String, String>();
                chats.put("user", uname);
                chats.put("message", message);
                chat.setValue(chats);
                saved = true;

            } catch (DatabaseException e) {
                e.printStackTrace();
                saved = false;
            }
        }
        return saved;
    }

    public void receiveChat(DataSnapshot dataSnapshot) {


        Iterator i = dataSnapshot.getChildren().iterator();
        ChatListManager chatList = new ChatListManager();
        while (i.hasNext()) {


            chatList.setChatMessage((String) ((DataSnapshot) i.next()).getValue());
            chatList.setChatUsername((String) ((DataSnapshot) i.next()).getValue());

            chatListArr.clear();
            chatListArr.add(chatList);

        }
    }
        public ArrayList<ChatListManager> retrieve ()
        {
            db.addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                    receiveChat(dataSnapshot);
                }

                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String s) {
                    receiveChat(dataSnapshot);
                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {
                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String s) {
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                }
            });
            return chatListArr;
        }
    }

ChatListAdapeter.java

public class ChatListAdapter extends BaseAdapter {

    Context context;
    ArrayList<ChatListManager> chatListArr;

    public ChatListAdapter(Context c,ArrayList<ChatListManager> chatListArray) {
        this.context = c;
        this.chatListArr = chatListArray;
    }

    @Override
    public int getCount() {
        return chatListArr.size();
    }

    @Override
    public Object getItem(int position) {
        return chatListArr.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if(convertView==null)
        {
            convertView= LayoutInflater.from(context).inflate(R.layout.layout_chat_listview_row,parent,false);

        }
        TextView uname= (TextView) convertView.findViewById(R.id.chatMessageUser);
        TextView message= (TextView) convertView.findViewById(R.id.chatMessageText);
        final ChatListManager s= (ChatListManager) this.getItem(position);
        uname.setText(s.getChatUsername());
        message.setText(s.getChatMessage());
        return convertView;
    }
}

ChatListManager.java

public class ChatListManager  {
    private String chatUsername;
    private String chatMessage;

    public ChatListManager() {

    }

    public ChatListManager(String chatUsername, String chatMessage){
        this.setChatUsername(chatUsername);
        this.setChatMessage(chatMessage);

    }
    public String getChatUsername() {

        return chatUsername;
    }

    public void setChatUsername(String chatUsername) {
        this.chatUsername = chatUsername;
    }

    public String getChatMessage() {
        return chatMessage;
    }

    public void setChatMessage(String chatMessage) {
        this.chatMessage = chatMessage;
    }
}

ChatFragment.java

public class ChatFragment extends Fragment implements View.OnClickListener {


    private EditText chatMessageBox;
    private Button chatSendButton;
    private DatabaseReference db;
    private ListView chatList;
    private FirebaseHelper firebaseHelper;
    private ChatListAdapter chatListAdapter;
    private ChatListManager chatListManager;

    public ChatFragment() {

    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        View chatView = inflater.inflate(R.layout.fragment_chatroom, container, false);


        chatMessageBox = (EditText) chatView.findViewById(R.id.chatMessageBox);
        chatSendButton = (Button) chatView.findViewById(R.id.chatSendButton);
        chatSendButton.setOnClickListener(this);

        db = FirebaseDatabase.getInstance().getReference().child("chat_room");
        firebaseHelper = new FirebaseHelper(db);
        chatListAdapter = new ChatListAdapter(getActivity().getApplicationContext(), firebaseHelper.retrieve());

        chatList = (ListView) chatView.findViewById(R.id.chatList);
        chatList.setAdapter(chatListAdapter);





        return chatView;
    }

    @Override
    public void onClick(View v) {
        if (v == chatSendButton) {

            String uname = SharedPrefManager.getInstance(getActivity().getApplicationContext()).getDetails("u_name");
            String message = chatMessageBox.getText().toString();
            chatListManager = new ChatListManager(uname,message);

            firebaseHelper.sendChat(chatListManager.getChatUsername(), chatListManager.getChatMessage());
            chatListAdapter.notifyDataSetChanged();

        }
    }
}

我的问题是，在 ListView 中，它不会从 firebase Db 加载聊天消息，而是显示我发送的消息。就像我附加的 AVD 输出文件一样

我是一名学生，我引用了一些 youtube 视频和 StackOverflow 问题来编写这些代码。

Answer 1

public void receiveChat(DataSnapshot dataSnapshot) {


        Iterator i = dataSnapshot.getChildren().iterator();
        ChatListManager chatList = new ChatListManager();
        while (i.hasNext()) {


            chatList.setChatMessage((String) ((DataSnapshot) i.next()).getValue());
            chatList.setChatUsername((String) ((DataSnapshot) i.next()).getValue());

            chatListArr.clear();
            chatListArr.add(chatList);

        }

应该是，

public void receiveChat(DataSnapshot dataSnapshot) {

        Iterator i = dataSnapshot.getChildren().iterator();
        while (i.hasNext()) {

            String message = (String) ((DataSnapshot) i.next()).getValue();
            String uname = (String) ((DataSnapshot) i.next()).getValue();
            ChatListManager chatList = new ChatListManager(uname,message);

            chatListArr.add(chatList);
        }
    }

经过几个小时的代码我终于找到了 self !!