如何显示回收站查看最近的聊天消息？

Question

我很新到Android / Java开发。我的工作，涉及到一个聊天活动项目。

我希望活动以自动滚动到聊天屏幕的底部（最近的聊天消息）。

我试着用吐司显示为getItem计数 - 我可以确认我可以正确地拿起我Recyclerview项目INT位置。不过，我奋力用ScrollToPosition或SmoothScroltoPosition得到我想要的结果。

任何想法，我怎么能自动滚动到我最近的聊天项目？

这里是我下面的聊天活动：

公共类ChatActivity扩展AppCompatActivity {

private RecyclerView mRecyclerView;
private RecyclerView.Adapter mChatAdapter;
private RecyclerView.LayoutManager mChatLayoutManager;
private  String currentUserID, matchId, chatId;

private EditText mSendEditText;
private Button mSend;

DatabaseReference mDatabaseChat;
DatabaseReference mDatabaseChatDB;


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

    matchId = getIntent().getExtras().getString("matchid");
    currentUserID = FirebaseAuth.getInstance().getCurrentUser().getUid();

    mDatabaseChat = FirebaseDatabase.getInstance().getReference().child("User").child(currentUserID).child("connections").child("matches").child(matchId).child("ChatId");
    mDatabaseChatDB = FirebaseDatabase.getInstance().getReference().child("Chat");

    getChatID();

    mSend = (Button) findViewById(R.id.send);
    mSendEditText = (EditText) findViewById(R.id.message);


    mSend.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            sendMessage();
        }

        private void sendMessage() {
            String sendMessageText = mSendEditText.getText().toString();
            if (!sendMessageText.isEmpty()){
                DatabaseReference newMessageDb = mDatabaseChatDB.push();

                Map newMessage = new HashMap<>();
                newMessage.put("createdByUser",currentUserID);
                newMessage.put("text", sendMessageText);

                newMessageDb.setValue(newMessage);
            }
            mSendEditText.setText(null);
        }
    });

    mRecyclerView = (RecyclerView) findViewById(R.id.chatview);
    mRecyclerView.setNestedScrollingEnabled(false);
    mRecyclerView.setHasFixedSize(false);
    mChatLayoutManager = new LinearLayoutManager(ChatActivity.this);
    mRecyclerView.setLayoutManager(mChatLayoutManager);
    mChatAdapter = new ChatAdapter(getDataSetChat(),ChatActivity.this);
    mRecyclerView.setAdapter(mChatAdapter);

}

private void getChatID(){
    mDatabaseChat.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            if (dataSnapshot.exists()) {
                chatId = dataSnapshot.getValue().toString();
                mDatabaseChatDB = mDatabaseChatDB.child(chatId);
                getChatMessages();
            }
        }

        private void getChatMessages() {
            mDatabaseChatDB.addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                    if (dataSnapshot.exists()){
                        String message = null;
                        String currentuser = null;

                        if (dataSnapshot.child("text").getValue() != null ){
                            message = dataSnapshot.child("text").getValue().toString();
                        }

                        if (dataSnapshot.child("createdByUser").getValue() != null ){
                            currentuser = dataSnapshot.child("createdByUser").getValue().toString();
                        }
                        if(message!= null && currentuser !=null){
                            Boolean currentUserBoolean = false;
                            if(currentuser.equals(currentUserID)){
                                currentUserBoolean = true;
                            }
                            ChatObject newMessage = new ChatObject(message,currentUserBoolean);
                            resultsChat.add(newMessage);
                            mChatAdapter.notifyDataSetChanged();
                        }
                    }
                }

                @Override
                public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

                }

                @Override
                public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {

                }

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

                }

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

                }
            });
        }

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

        }
    });
}
private ArrayList<ChatObject> resultsChat = new ArrayList<ChatObject>();
private List<ChatObject> getDataSetChat() {
    return resultsChat;
}

}

Answer 1

你好@Asif斌Zahit用于获取顶部的最近消息，你必须做出这样的代码下面的一些变化

在数组列表resultsChat.add（NewMessage作为）加入最新消息，你必须在数组列表中降序排序，然后调用notifyDataSetChanged后后

如果您设置适配器，然后才在列表中已经记录，你必须排序列表的下方，该组适配器回收后视图描述

Collections.sort(getDataSetChat())
mChatAdapter = new ChatAdapter(getDataSetChat(),ChatActivity.this);
mRecyclerView.setAdapter(mChatAdapter);

当添加新的消息列表

resultsChat.add(newMessage);
Collections.sort(resultsChat);
mChatAdapter.notifyDataSetChanged();

它将随时添加您的最新消息，在recyclerview名列榜首