Firebase中的Listview在listview中两次显示相同的消息

Question

我有一个应用程序，它涉及消息传递，它发送和显示非常好，但是它在 listView 中两次显示相同的消息，我真的不明白，我见过其他类似的问题，但是它们都是量身定制的对于那个特定的问题，这是我的代码：

聊天活动（每当发送消息时都会调用它）：

private void append_chat_conversation(DataSnapshot dataSnapshot) {
        for (DataSnapshot ds : dataSnapshot.getChildren()) {
            Log.e("Chat details: ", String.valueOf(ds));
            chat_username = dataSnapshot.child("username").getValue(String.class);
            chat_msg = dataSnapshot.child("message").getValue(String.class);

            Chat chat = new Chat(chat_username, chat_msg);
            chatList.add(chat);
            Log.e("Chat username: ", "" + chat_username);
            Log.e("Chat message: ", "" + chat_msg);
        }
        adapter.notifyDataSetChanged();
    }

我的聊天列表适配器：

public class chatListAdapter extends ArrayAdapter<Chat> {

    private Context mContext;
    int mResource;
    TextView usernameTV, messageTV;

    public chatListAdapter(Context context, int resource, ArrayList<Chat> objects) {
        super(context, resource, objects);
        mContext = context;
        mResource = resource;

    }

    @NonNull
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        String username = getItem(position).getUsername();
        String message = getItem(position).getMessage();

        Chat chat = new Chat(username, message);

        LayoutInflater inflater = LayoutInflater.from(mContext);
        convertView = inflater.inflate(mResource, parent, false);


        usernameTV = convertView.findViewById(R.id.username_chat);
        messageTV = convertView.findViewById(R.id.message_chat);

        usernameTV.setText(username);
        messageTV.setText(message);

        return convertView;
    }
}

聊天模型：

public class Chat {
    private String username, message;

    public Chat(String username, String message) {
        this.username = username;
        this.message = message;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

提前感谢您的帮助！

插件：

我的事件监听器：

chatURLRoot.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                chatList.clear();
                append_chat_conversation(dataSnapshot);
            }

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

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {

            }

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

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

    }

然后，每当发送消息时，它都会调用此方法：

public String chat_msg, chat_username;

    private void append_chat_conversation(DataSnapshot dataSnapshot) {
        for (DataSnapshot ds : dataSnapshot.getChildren()) {
            Log.e("Chat details: ", String.valueOf(ds));
            chat_username = dataSnapshot.child("username").getValue(String.class);
            chat_msg = dataSnapshot.child("message").getValue(String.class);

            Chat chat = new Chat(chat_username, chat_msg);
            chatList.add(chat);
            Log.e("Chat username: ", "" + chat_username);
            Log.e("Chat message: ", "" + chat_msg);
        }
        adapter.notifyDataSetChanged();
    }

Answer 1

在添加新的DataSnapshot 之前，您必须清除您的列表，如下所示

private void append_chat_conversation(DataSnapshot dataSnapshot) {
        chatList.clear();
        for (DataSnapshot ds : dataSnapshot.getChildren()) {
            Log.e("Chat details: ", String.valueOf(ds));
            chat_username = dataSnapshot.child("username").getValue(String.class);
            chat_msg = dataSnapshot.child("message").getValue(String.class);

            Chat chat = new Chat(chat_username, chat_msg);
            chatList.add(chat);
            Log.e("Chat username: ", "" + chat_username);
            Log.e("Chat message: ", "" + chat_msg);
        }
        adapter.notifyDataSetChanged();
    }