基于Android实现SQLiteOpenHelper的继承类MyHelper，创建数据表user，字段包括自增id、username、password等三个字段，并插入三条记录. 在MainActivity类中实现对数据库增删改查操作，并在用查询或者命令行的方法观察数据库的变化。

好的，我会尽力回答你的问题。以下是基于Android实现SQLiteOpenHelper的继承类MyHelper，创建数据表user，字段包括自增id、username、password等三个字段，并插入三条记录的代码：

public class MyHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "my_database";
    private static final int DATABASE_VERSION = 1;

    private static final String TABLE_NAME = "user";
    private static final String COLUMN_ID = "id";
    private static final String COLUMN_USERNAME = "username";
    private static final String COLUMN_PASSWORD = "password";

    private static final String SQL_CREATE_TABLE =
            "CREATE TABLE " + TABLE_NAME + " (" +
                    COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
                    COLUMN_USERNAME + " TEXT," +
                    COLUMN_PASSWORD + " TEXT)";

    public MyHelper(Context context){
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(SQL_CREATE_TABLE);
        ContentValues values = new ContentValues();
        values.put(COLUMN_USERNAME, "user1");
        values.put(COLUMN_PASSWORD, "password1");
        db.insert(TABLE_NAME, null, values);
        values.clear();
        values.put(COLUMN_USERNAME, "user2");
        values.put(COLUMN_PASSWORD, "password2");
        db.insert(TABLE_NAME, null, values);
        values.clear();
        values.put(COLUMN_USERNAME, "user3");
        values.put(COLUMN_PASSWORD, "password3");
        db.insert(TABLE_NAME, null, values);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

在MainActivity类中实现对数据库增删改查操作，可以在onCreate方法中获取数据库实例并进行操作，如下所示：

public class MainActivity extends AppCompatActivity {

    private MyHelper dbHelper;

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

        dbHelper = new MyHelper(this);
        SQLiteDatabase db = dbHelper.getWritableDatabase();

        // 增加数据
        ContentValues values = new ContentValues();
        values.put(MyHelper.COLUMN_USERNAME, "user4");
        values.put(MyHelper.COLUMN_PASSWORD, "password4");
        db.insert(MyHelper.TABLE_NAME, null, values);

        // 删除数据
        String selection = MyHelper.COLUMN_USERNAME + "=?";
        String[] selectionArgs = {"user1"};
        db.delete(MyHelper.TABLE_NAME, selection, selectionArgs);

        // 更新数据
        values.clear();
        values.put(MyHelper.COLUMN_PASSWORD, "new_password");
        String whereClause = MyHelper.COLUMN_USERNAME + "=?";
        String[] whereArgs = {"user2"};
        db.update(MyHelper.TABLE_NAME, values, whereClause, whereArgs);

        // 查询数据
        String[] projection = {
                MyHelper.COLUMN_ID,
                MyHelper.COLUMN_USERNAME,
                MyHelper.COLUMN_PASSWORD
        };
        Cursor cursor = db.query(MyHelper.TABLE_NAME, projection, null, null, null, null, null);
        while (cursor.moveToNext()) {
            int id = cursor.getInt(cursor.getColumnIndex(MyHelper.COLUMN_ID));
            String username = cursor.getString(cursor.getColumnIndex(MyHelper.COLUMN_USERNAME));
            String password = cursor.getString(cursor.getColumnIndex(MyHelper.COLUMN_PASSWORD));
            Log.d("MainActivity", "id:" + id + ", username:" + username + ", password:" + password);
        }
        cursor.close();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        dbHelper.close();
    }
}

其中，增加数据使用db.insert方法，删除数据使用db.delete方法，更新数据使用db.update方法，查询数据使用db.query方法。最后在onDestroy方法中关闭数据库。你可以通过命令行或者Android Studio的Database Inspector来观察数据库的变化。