Flutter:scrollController.isAttachedisalwaysfalse

当调用scrollController.isAttached时，它在第一帧之前是始终false的。解决方法是在第一帧之后检查isAttached属性，代码示例如下：

import 'package:flutter/material.dart';

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  late final ScrollController _scrollController;
  bool _isControllerAttached = false;

  @override
  void initState() {
    super.initState();
    _scrollController = ScrollController();
    WidgetsBinding.instance?.addPostFrameCallback((timeStamp) {
      setState(() {
        _isControllerAttached = _scrollController.hasClients;
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ListView.builder(
        controller: _scrollController,
        itemBuilder: (context, index) => ListTile(
          title: Text('Item $index'),
        ),
        itemCount: 100,
      ),
      bottomNavigationBar: _isControllerAttached
          ? const BottomNavigationBar(items: <BottomNavigationBarItem>[])
          : null,
    );
  }
}