android studio实现简单的QQ应用并写出代码

由于涉及到很多复杂的功能，这里只提供一个简单的实现思路，代码可能不完整，仅供参考。

1. 布局文件activity_qq.xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

  <androidx.recyclerview.widget.RecyclerView
      android:id="@+id/recycler_view"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:layout_above="@+id/input_layout"
      android:padding="16dp" />

  <LinearLayout
      android:id="@+id/input_layout"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_alignParentBottom="true"
      android:orientation="horizontal"
      android:padding="8dp">

    <EditText
        android:id="@+id/input_edit_text"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:hint="请输入消息" />

    <Button
        android:id="@+id/send_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="发送" />
  </LinearLayout>

</RelativeLayout>

2. 聊天消息类Message.java：

public class Message {
    private String sender; // 发送者
    private String receiver; // 接收者
    private String content; // 内容
    private Date time; // 时间

    public Message(String sender, String receiver, String content, Date time) {
        this.sender = sender;
        this.receiver = receiver;
        this.content = content;
        this.time = time;
    }

    public String getSender() {
        return sender;
    }

    public void setSender(String sender) {
        this.sender = sender;
    }

    public String getReceiver() {
        return receiver;
    }

    public void setReceiver(String receiver) {
        this.receiver = receiver;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

    public Date getTime() {
        return time;
    }

    public void setTime(Date time) {
        this.time = time;
    }
}

3. RecyclerView的Adapter类MessageAdapter.java：

public class MessageAdapter extends RecyclerView.Adapter<MessageAdapter.ViewHolder> {
    private List<Message> mMessageList;

    static class ViewHolder extends RecyclerView.ViewHolder {
        TextView senderTextView;
        TextView timeTextView;
        TextView contentTextView;

        public ViewHolder(View view) {
            super(view);
            senderTextView = view.findViewById(R.id.sender_text_view);
            timeTextView = view.findViewById(R.id.time_text_view);
            contentTextView = view.findViewById(R.id.content_text_view);
        }
    }

    public MessageAdapter(List<Message> messageList) {
        mMessageList = messageList;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.item_message, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Message message = mMessageList.get(position);
        holder.senderTextView.setText(message.getSender());
        holder.timeTextView.setText(message.getTime().toString());
        holder.contentTextView.setText(message.getContent());
    }

    @Override
    public int getItemCount() {
        return mMessageList.size();
    }
}

4. RecyclerView的item布局文件item_message.xml：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

  <TextView
      android:id="@+id/sender_text_view"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:textStyle="bold" />

  <TextView
      android:id="@+id/time_text_view"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:textSize="12sp" />

  <TextView
      android:id="@+id/content_text_view"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content" />

</LinearLayout>

5. MainActivity.java：

public class MainActivity extends AppCompatActivity {
    private List<Message> mMessageList = new ArrayList<>();
    private EditText mInputEditText;
    private MessageAdapter mAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        RecyclerView recyclerView = findViewById(R.id.recycler_view);
        mInputEditText = findViewById(R.id.input_edit_text);
        Button sendButton = findViewById(R.id.send_button);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);
        mAdapter = new MessageAdapter(mMessageList);
        recyclerView.setAdapter(mAdapter);
        sendButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String content = mInputEditText.getText().toString();
                if (!TextUtils.isEmpty(content)) {
                    Message message = new Message("me", "other", content, new Date());
                    mMessageList.add(message);
                    mAdapter.notifyItemInserted(mMessageList.size() - 1);
                    recyclerView.scrollToPosition(mMessageList.size() - 1);
                    mInputEditText.setText("");
                }
            }
        });
    }
}

这样就实现了一个简单的聊天界面，可以输入消息并发送到RecyclerView中显示。但是缺少一些重要的功能，比如消息推送、接收消息、显示未读消息数等等。如果要实现一个完整的QQ应用，需要更加复杂的代码和逻辑。