dart
import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('学生信息分页加载'),
        ),
        body: StudentList(),
      ),
    );
  }
}

class StudentList extends StatefulWidget {
  @override
  _StudentListState createState() => _StudentListState();
}

class _StudentListState extends State<StudentList> {
  int _page = 1; // 当前页码
  final int _pageSize = 20; // 每页数据量

  // 模拟从 API 获取学生数据
  Future<List<String>> _fetchStudents() async {
    await Future.delayed(const Duration(seconds: 2)); // 模拟网络延迟
    final start = (_page - 1) * _pageSize;
    final end = start + _pageSize;
    final students = List.generate(100, (index) => '学生 ${index + 1}');
    final result = students.sublist(start, end > students.length ? students.length : end);
    _page++; // 增加页码
    return result;
  }

  @override
  Widget build(BuildContext context) {
    return LoadMore(
      loadData: _fetchStudents,
      builder: (data, controller) {
        return ListView.builder(
          controller: controller, // 绑定 ScrollController
          itemCount: data.length,
          itemBuilder: (context, index) {
            return ListTile(
              title: Text(data[index]),
            );
          },
        );
      },
      loadingWidget: const Padding(
        padding: EdgeInsets.all(16.0),
        child: CircularProgressIndicator(),
      ),
      noMoreDataWidget: const Padding(
        padding: EdgeInsets.all(16.0),
        child: Text('没有更多学生信息了'),
      ),
    );
  }
}


class LoadMore extends StatefulWidget {
  final Future<List<String>> Function() loadData; // 加载数据的回调
  final Widget Function(List<String> data, ScrollController controller) builder; // 构建列表的 Widget
  final Widget? loadingWidget; // 加载中的 Widget
  final Widget? noMoreDataWidget; // 没有更多数据时的 Widget

  const LoadMore({
    Key? key,
    required this.loadData,
    required this.builder,
    this.loadingWidget,
    this.noMoreDataWidget,
  }) : super(key: key);

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

class _LoadMoreState extends State<LoadMore> {
  final List<String> _data = []; // 存储加载的数据
  bool _isLoading = false; // 是否正在加载
  bool _hasMore = true; // 是否还有更多数据
  final ScrollController _scrollController = ScrollController(); // 滚动控制器
  bool _showScrollButton = false; // 是否显示滚动按钮
  bool _isScrollingManually = false; // 是否正在手动滚动

  @override
  void initState() {
    super.initState();
    _loadData(); // 初始化时加载数据
    _scrollController.addListener(_onScroll); // 监听滚动事件
  }

  @override
  void dispose() {
    _scrollController.removeListener(_onScroll);
    _scrollController.dispose();
    super.dispose();
  }

  void _onScroll() {
    // 监听滚动位置，动态显示或隐藏按钮
    if (_scrollController.position.pixels == _scrollController.position.maxScrollExtent) {
      setState(() {
        _showScrollButton = false; // 滚动到底部时隐藏按钮
      });
    } else {
      setState(() {
        _showScrollButton = true; // 滚动时显示按钮
      });
    }

    // 如果不是手动滚动，且滚动到底部，则触发加载更多数据
    if (!_isScrollingManually &&
        _scrollController.position.pixels == _scrollController.position.maxScrollExtent) {
      _loadData();
    }
  }

  Future<void> _loadData() async {
    if (_isLoading || !_hasMore) return;

    setState(() {
      _isLoading = true;
    });

    // 调用外部传入的加载数据方法
    final newData = await widget.loadData();

    setState(() {
      _data.addAll(newData);
      _isLoading = false;
      _hasMore = newData.isNotEmpty; // 如果没有新数据，说明没有更多数据了
    });
  }

  void _scrollToBottom() {
    // 标记为手动滚动
    _isScrollingManually = true;

    // 滚动到列表底部
    _scrollController.animateTo(
      _scrollController.position.maxScrollExtent,
      duration: const Duration(milliseconds: 300),
      curve: Curves.easeOut,
    ).then((_) {
      // 滚动完成后，取消手动滚动标记
      _isScrollingManually = false;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Stack(
      children: [
        NotificationListener<ScrollNotification>(
          onNotification: (notification) {
            // 监听滚动事件
            if (notification is ScrollEndNotification &&
                notification.metrics.pixels == notification.metrics.maxScrollExtent) {
              if (!_isScrollingManually) {
                _loadData(); // 滚动到底部时加载更多数据
              }
            }
            return true;
          },
          child: Column(
            children: [
              Expanded(
                child: widget.builder(_data, _scrollController), // 构建列表
              ),
              if (_isLoading)
                widget.loadingWidget ??
                    const Padding(
                      padding: EdgeInsets.all(16.0),
                      child: CircularProgressIndicator(),
                    ),
              if (!_hasMore && _data.isNotEmpty)
                widget.noMoreDataWidget ??
                    const Padding(
                      padding: EdgeInsets.all(16.0),
                      child: Text('没有更多数据了'),
                    ),
            ],
          ),
        ),
        if (_showScrollButton)
          Positioned(
            bottom: 20,
            right: 20,
            child: FloatingActionButton(
              onPressed: _scrollToBottom,
              child: const Icon(Icons.arrow_downward),
            ),
          ),
      ],
    );
  }
}