在android studio中使用SQLite显示上次登录的用户数据

// 数据库助手类
public class DBHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "user.db";
    private static final int DATABASE_VERSION = 1;
    private static final String TABLE_NAME = "user";
    private static final String COLUMN_USERNAME = "username";
    private static final String COLUMN_PASSWORD = "password";

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

    @Override
    public void onCreate(SQLiteDatabase db) {
        String createTableQuery = "CREATE TABLE " + TABLE_NAME + " (" +
                COLUMN_USERNAME + " TEXT PRIMARY KEY, " +
                COLUMN_PASSWORD + " TEXT)";
        db.execSQL(createTableQuery);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // 数据库升级操作
    }
}

// 用户数据模型类
public class User {
    private String username;
    private String password;

    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }

    // getter和setter方法
}

// 登录功能实现
public class LoginActivity extends AppCompatActivity {
    private EditText usernameEditText;
    private EditText passwordEditText;
    private DBHelper dbHelper;

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

        usernameEditText = findViewById(R.id.usernameEditText);
        passwordEditText = findViewById(R.id.passwordEditText);
        dbHelper = new DBHelper(this);
    }

    public void login(View view) {
        String username = usernameEditText.getText().toString();
        String password = passwordEditText.getText().toString();

        SQLiteDatabase db = dbHelper.getWritableDatabase();
        String query = "SELECT * FROM " + DBHelper.TABLE_NAME +
                " WHERE " + DBHelper.COLUMN_USERNAME + " = ? AND " +
                DBHelper.COLUMN_PASSWORD + " = ?";
        Cursor cursor = db.rawQuery(query, new String[]{username, password});

        if (cursor.moveToFirst()) {
            // 登录成功，保存用户信息到SharedPreferences或其他持久化方式中
            String savedUsername = cursor.getString(cursor.getColumnIndex(DBHelper.COLUMN_USERNAME));
            String savedPassword = cursor.getString(cursor.getColumnIndex(DBHelper.COLUMN_PASSWORD));
            User user = new User(savedUsername, savedPassword);
            // 保存用户信息
        } else {
            // 登录失败
        }

        cursor.close();
        dbHelper.close();
    }
}

// 显示上次登录用户数据
public class MainActivity extends AppCompatActivity {
    private TextView usernameTextView;
    private DBHelper dbHelper;

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

        usernameTextView = findViewById(R.id.usernameTextView);
        dbHelper = new DBHelper(this);

        // 查询上次登录的用户数据
        SQLiteDatabase db = dbHelper.getReadableDatabase();
        String query = "SELECT * FROM " + DBHelper.TABLE_NAME;
        Cursor cursor = db.rawQuery(query, null);

        if (cursor.moveToLast()) {
            String username = cursor.getString(cursor.getColumnIndex(DBHelper.COLUMN_USERNAME));
            usernameTextView.setText(username);
        }

        cursor.close();
        dbHelper.close();
    }
}