android开发一个记事本代码

以下是一个简单的 Android 记事本应用的代码，包含保存、读取、清空、撤销、重做、搜索和分享功能：

MainActivity.java

import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.EditText;
import android.widget.Toast;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.Stack;

public class MainActivity extends AppCompatActivity {
    private EditText editText;
    private Stack<String> undoStack = new Stack<>();
    private Stack<String> redoStack = new Stack<>();

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

        editText = findViewById(R.id.editText);

        // 添加输入框的监听器，当输入框中的内容发生变化时自动保存
        editText.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                // 将当前内容保存到撤销栈中
                undoStack.push(s.toString());
            }

            @Override
            public void afterTextChanged(Editable s) {
            }
        });

        // 读取保存的内容
        String text = readText();
        editText.setText(text);
        editText.setSelection(text.length());
    }

    // 创建菜单
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    // 处理菜单点击事件
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        switch (id) {
            case R.id.action_save:
                // 保存输入框中的内容
                saveText();
                return true;
            case R.id.action_load:
                // 读取保存的内容
                String text = readText();
                editText.setText(text);
                editText.setSelection(text.length());
                return true;
            case R.id.action_clear:
                // 清空输入框中的内容
                editText.setText("");
                return true;
            case R.id.action_undo:
                // 撤销操作
                if (!undoStack.isEmpty()) {
                    String text1 = undoStack.pop();
                    redoStack.push(text1);
                    if (!undoStack.isEmpty()) {
                        String text2 = undoStack.peek();
                        editText.setText(text2);
                        editText.setSelection(text2.length());
                    } else {
                        editText.setText("");
                    }
                }
                return true;
            case R.id.action_redo:
                // 重做操作
                if (!redoStack.isEmpty()) {
                    String text1 = redoStack.pop();
                    undoStack.push(text1);
                    editText.setText(text1);
                    editText.setSelection(text1.length());
                }
                return true;
            case R.id.action_search:
                // 搜索输入框中的内容
                Intent intent = new Intent(Intent.ACTION_SEND);
                intent.setType("text/plain");
                intent.putExtra(Intent.EXTRA_TEXT, editText.getText().toString());
                startActivity(Intent.createChooser(intent, "分享到"));
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }

    // 保存输入框中的内容到文件中
    private void saveText() {
        try {
            File file = new File(getFilesDir(), "note.txt");
            FileOutputStream fos = new FileOutputStream(file);
            OutputStreamWriter osw = new OutputStreamWriter(fos);
            osw.write(editText.getText().toString());
            osw.close();
            Toast.makeText(MainActivity.this, "保存成功", Toast.LENGTH_SHORT).show();
        } catch (Exception e) {
            e.printStackTrace();
            Toast.makeText(MainActivity.this, "保存失败", Toast.LENGTH_SHORT).show();
        }
    }

    // 从文件中读取保存的内容
    private String readText() {
        StringBuilder sb = new StringBuilder();
        try {
            File file = new File(getFilesDir(), "note.txt");
            FileInputStream fis = new FileInputStream(file);
            InputStreamReader isr = new InputStreamReader(fis);
            BufferedReader br = new BufferedReader(isr);
            String line;
            while ((line = br.readLine()) != null) {
                sb.append(line).append('\n');
            }
            br.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return sb.toString();
    }
}

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/editText"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scrollbars="vertical" />

</RelativeLayout>

menu_main.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <item
        android:id="@+id/action_save"
        android:title="保存"
        app:showAsAction="always" />

    <item
        android:id="@+id/action_load"
        android:title="读取"
        app:showAsAction="always" />

    <item
        android:id="@+id/action_clear"
        android:title="清空"
        app:showAsAction="always" />

    <item
        android:id="@+id/action_undo"
        android:title="撤销"
        app:showAsAction="ifRoom" />

    <item
        android:id="@+id/action_redo"
        android:title="重做"
        app:showAsAction="ifRoom" />

    <item
        android:id="@+id/action_search"
        android:title="分享"
        app:showAsAction="never" />

</menu>

注意：上述代码仅供参考，实际应用需要根据具体需求进行修改和扩展。