改良《第一行代码》第二版第三章制作聊天界面并保存聊天数据，做法如下：在主界面发放置一个RecycleView用于显示聊天信息内容，又放置一个EditText用于输入消息，还放置一个Button用于发送消息。使用SharedPreferences保存发送的消息数据，下次再打开该界面时，已发送的消息仍保存在界面上

好的，下面是改良版的代码实现：

1. 在布局文件中添加RecycleView、EditText和Button控件

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/chat_recycler_view"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1"/>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:padding="8dp">

    <EditText
        android:id="@+id/chat_input_edit_text"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:hint="@string/chat_input_hint"/>

    <Button
        android:id="@+id/chat_send_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/chat_send_button_text"/>
</LinearLayout>

2. 创建一个ChatAdapter类用于显示聊天信息

public class ChatAdapter extends RecyclerView.Adapter<ChatAdapter.ViewHolder> {
    private List<String> mChatList;

    static class ViewHolder extends RecyclerView.ViewHolder {
        TextView chatText;

        public ViewHolder(View view) {
            super(view);
            chatText = view.findViewById(R.id.chat_text);
        }
    }

    public ChatAdapter(List<String> chatList) {
        mChatList = chatList;
    }

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

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        String chat = mChatList.get(position);
        holder.chatText.setText(chat);
    }

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

3. 在MainActivity中初始化RecycleView、EditText和Button控件，以及从SharedPreferences中读取已发送的消息数据

public class MainActivity extends AppCompatActivity {
    private List<String> mChatList = new ArrayList<>();
    private ChatAdapter mAdapter;
    private SharedPreferences mSharedPreferences;
    private EditText mInputEditText;
    private RecyclerView mRecyclerView;

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

        mSharedPreferences = getSharedPreferences("chat_data", MODE_PRIVATE);
        Set<String> chatSet = mSharedPreferences.getStringSet("chat_list", new HashSet<String>());
        mChatList.addAll(chatSet);

        mAdapter = new ChatAdapter(mChatList);
        mRecyclerView = findViewById(R.id.chat_recycler_view);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(MainActivity.this));
        mRecyclerView.setAdapter(mAdapter);

        mInputEditText = findViewById(R.id.chat_input_edit_text);
        Button sendButton = findViewById(R.id.chat_send_button);
        sendButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String inputText = mInputEditText.getText().toString();
                if (!TextUtils.isEmpty(inputText)) {
                    mChatList.add(inputText);
                    mAdapter.notifyItemInserted(mChatList.size() - 1);
                    mRecyclerView.scrollToPosition(mChatList.size() - 1);

                    SharedPreferences.Editor editor = mSharedPreferences.edit();
                    editor.putStringSet("chat_list", new HashSet<>(mChatList));
                    editor.apply();

                    mInputEditText.setText("");
                }
            }
        });
    }
}

4. 创建一个chat_item.xml布局文件用于显示聊天信息

<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/chat_text"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="16dp"
    android:textSize="16sp"/>

这样，就完成了在主界面制作聊天界面并保存聊天数据的改良版实现。