传统：

class RouterManager {
  // 单例模式
  static final RouterManager _instance = RouterManager._internal();

  factory RouterManager() {
    return _instance;
  }

  RouterManager._internal();
}

传递参数进行初始化时：

class RouterManager {
  // 私有静态实例，确保单例
  static RouterManager? _instance;

  // goRouter 是 final 变量，确保它只被初始化一次
  final GoRouter goRouter;

  // 私有构造函数
  RouterManager._internal(this.goRouter);

  // 工厂方法，返回 RouterManager 实例
  factory RouterManager({String initialLocation = '/'}) {
    _instance ??= RouterManager._internal(buildRouter(initialLocation));
    return _instance!;
  }

  static GoRouter buildRouter(String initialLocation) {
    return GoRouter(
      initialLocation: initialLocation,
      routes: [
        GoRoute(path: '/', builder: (context, state) => const SplashPage()),
        GoRoute(path: '/home', builder: (context, state) => const HomePage()),
        GoRoute(
          path: '/detail/:id',
          builder: (context, state) {
            final id = state.pathParameters['id']!;
            return DetailPage(id: id);
          },
        ),
      ],
      errorBuilder:
          (context, state) => Scaffold(body: Center(child: Text('Error: ${state.error}'))),
    );
  }
}