android studio记事本app完整代码

以下是一个简单的 Android Studio 记事本应用的完整代码。这个应用包括基本的文本编辑功能，例如创建、打开、保存和编辑文本文件。

MainActivity.java

import android.content.Context;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
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.IOException;
import java.io.InputStreamReader;

public class MainActivity extends AppCompatActivity {

    private EditText mEditText;

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

        mEditText = (EditText) findViewById(R.id.edit_text);
    }

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

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        switch (id) {
            case R.id.action_new:
                newFile();
                break;
            case R.id.action_open:
                openFile();
                break;
            case R.id.action_save:
                saveFile();
                break;
        }

        return super.onOptionsItemSelected(item);
    }

    private void newFile() {
        mEditText.setText("");
        Toast.makeText(this, "New file created", Toast.LENGTH_SHORT).show();
    }

    private void openFile() {
        File file = getFileStreamPath("note.txt");
        if (file.exists()) {
            try {
                FileInputStream fis = openFileInput("note.txt");
                InputStreamReader isr = new InputStreamReader(fis);
                BufferedReader br = new BufferedReader(isr);

                StringBuilder sb = new StringBuilder();
                String line;

                while ((line = br.readLine()) != null) {
                    sb.append(line);
                    sb.append("\n");
                }

                mEditText.setText(sb.toString());

                br.close();
                isr.close();
                fis.close();

                Toast.makeText(this, "File opened", Toast.LENGTH_SHORT).show();
            } catch (IOException e) {
                e.printStackTrace();
            }
        } else {
            Toast.makeText(this, "File does not exist", Toast.LENGTH_SHORT).show();
        }
    }

    private void saveFile() {
        String text = mEditText.getText().toString();

        try {
            FileOutputStream fos = openFileOutput("note.txt", Context.MODE_PRIVATE);
            fos.write(text.getBytes());
            fos.close();

            Toast.makeText(this, "File saved", Toast.LENGTH_SHORT).show();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/edit_text"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="top|left"
        android:inputType="textMultiLine"
        android:scrollbars="vertical" />

</RelativeLayout>

menu_main.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/action_new"
        android:title="New"
        android:icon="@android:drawable/ic_menu_add"
        android:showAsAction="ifRoom" />
    <item
        android:id="@+id/action_open"
        android:title="Open"
        android:icon="@android:drawable/ic_menu_gallery"
        android:showAsAction="ifRoom" />
    <item
        android:id="@+id/action_save"
        android:title="Save"
        android:icon="@android:drawable/ic_menu_save"
        android:showAsAction="ifRoom" />
</menu>