android 利用数据库写一个登陆注册

好的，下面是一个简单的 Android 登录注册示例程序，使用 SQLite 数据库存储用户信息。

1. 创建一个名为 `User` 的 Java 类，表示一个用户对象，包含用户名和密码属性：

public class User {
    private String username;
    private String password;

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

    public String getUsername() {
        return username;
    }

    public String getPassword() {
        return password;
    }
}

2. 在 `MainActivity` 中创建数据库和表：

public class MainActivity extends AppCompatActivity {
    private static final String DB_NAME = "users.db";
    private static final int DB_VERSION = 1;
    private static final String TABLE_NAME = "users";
    private static final String COLUMN_USERNAME = "username";
    private static final String COLUMN_PASSWORD = "password";

    private SQLiteDatabase database;

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

        // 创建数据库和表
        database = openOrCreateDatabase(DB_NAME, MODE_PRIVATE, null);
        database.execSQL(
                "CREATE TABLE IF NOT EXISTS " + TABLE_NAME +
                        " (" + COLUMN_USERNAME + " TEXT PRIMARY KEY, " +
                        COLUMN_PASSWORD + " TEXT)"
        );
    }
}

3. 实现注册功能，在注册界面中输入用户名和密码，点击按钮添加到数据库中：

public class RegisterActivity extends AppCompatActivity {
    private EditText usernameEditText;
    private EditText passwordEditText;
    private Button registerButton;

    private SQLiteDatabase database;

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

        // 打开数据库
        database = openOrCreateDatabase(MainActivity.DB_NAME, MODE_PRIVATE, null);

        usernameEditText = findViewById(R.id.usernameEditText);
        passwordEditText = findViewById(R.id.passwordEditText);
        registerButton = findViewById(R.id.registerButton);
        registerButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // 获取用户名和密码
                String username = usernameEditText.getText().toString();
                String password = passwordEditText.getText().toString();

                // 将用户添加到数据库
                ContentValues values = new ContentValues();
                values.put(MainActivity.COLUMN_USERNAME, username);
                values.put(MainActivity.COLUMN_PASSWORD, password);
                database.insert(MainActivity.TABLE_NAME, null, values);

                // 注册成功，返回登录界面
                Toast.makeText(RegisterActivity.this, "注册成功", Toast.LENGTH_SHORT).show();
                finish();
            }
        });
    }
}

4. 实现登录功能，在登录界面中输入用户名和密码，点击按钮从数据库中查找用户信息：

public class LoginActivity extends AppCompatActivity {
    private EditText usernameEditText;
    private EditText passwordEditText;
    private Button loginButton;
    private TextView registerTextView;

    private SQLiteDatabase database;

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

        // 打开数据库
        database = openOrCreateDatabase(MainActivity.DB_NAME, MODE_PRIVATE, null);

        usernameEditText = findViewById(R.id.usernameEditText);
        passwordEditText = findViewById(R.id.passwordEditText);
        loginButton = findViewById(R.id.loginButton);
        loginButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // 获取用户名和密码
                String username = usernameEditText.getText().toString();
                String password = passwordEditText.getText().toString();

                // 在数据库中查找用户
                Cursor cursor = database.query(
                        MainActivity.TABLE_NAME,
                        null,
                        MainActivity.COLUMN_USERNAME + " = ? AND " + MainActivity.COLUMN_PASSWORD + " = ?",
                        new String[]{username, password},
                        null,
                        null,
                        null
                );
                if (cursor.moveToFirst()) {
                    // 登录成功，跳转到主界面
                    Toast.makeText(LoginActivity.this, "登录成功", Toast.LENGTH_SHORT).show();
                    Intent intent = new Intent(LoginActivity.this, MainActivity.class);
                    startActivity(intent);
                    finish();
                } else {
                    // 登录失败，提示用户
                    Toast.makeText(LoginActivity.this, "用户名或密码错误", Toast.LENGTH_SHORT).show();
                }
            }
        });

        registerTextView = findViewById(R.id.registerTextView);
        registerTextView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // 跳转到注册界面
                Intent intent = new Intent(LoginActivity.this, RegisterActivity.class);
                startActivity(intent);
            }
        });
    }
}

以上就是一个简单的 Android 登录注册示例程序，使用 SQLite 数据库存储用户信息。