flutter命名路由传参奇怪的经历

main.dart文件内容：

import 'package:flutter/material.dart';
import 'pages/tabspages/tabs.dart';
import 'routers/Routes.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
   @override
  Widget build(BuildContext context) {
    return MaterialApp(
        home: Tabs(), initialRoute: "/", onGenerateRoute: onGenerateRoute);
  }
}

Routes.dart：

import 'package:flutter/material.dart';
import '../pages/tabspages/tabs.dart';
import '../pages/tabspages/FormPage.dart';
import '../pages/tabspages/SearchPage.dart';

final routes = {
  '/': (context) => Tabs(),
  '/form': (context) => FormPage(),
  '/search': (context, {arguments}) => SearchPage(arguments: arguments),
};

//固定写法
var onGenerateRoute = (RouteSettings settings) {
  // 统一处理
  final String name = settings.name;
  final Function pageContentBuilder = routes[name];
  if (pageContentBuilder != null) {
    if (settings.arguments != null) {
      final Route route = MaterialPageRoute(
          builder: (context) =>
              pageContentBuilder(context, arguments: settings.arguments));
      return route;
    } else {
      final Route route =
          MaterialPageRoute(builder: (context) => pageContentBuilder(context));
      return route;
    }
  }
};

setting.dart:

import 'package:flutter/material.dart';
class SettingPage extends StatelessWidget {
  const SettingPage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        children: [
          RaisedButton(
            onPressed: () {
              Navigator.pushNamed(context, "/search", arguments: {"id": 1234});
            },
            child: Text("点我跳转到搜索页面"),
          )
        ],
      ),
    );
  }
}

SearchPage.dart:

import 'package:flutter/material.dart';

class SearchPage extends StatelessWidget {
  final arguments;

  SearchPage({this.arguments});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("搜索页面"),
      ),
      body: Text("搜索页面内容区域${arguments != null ? arguments['id'] : '0'}"),
    );
  }
}

Routes.dart文件的onGenerateRoute回调放在main.dart里面路由跳转不了（玄学）