ScrollMetrics (Notification)

main.dart

import 'package:flutter/material.dart';

void main() => runApp(const ScrollMetricsDemo());

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

  @override
  State<ScrollMetricsDemo> createState() => ScrollMetricsDemoState();
}

class ScrollMetricsDemoState extends State<ScrollMetricsDemo> {
  int itemCount = 9;
  final ScrollController scrollController =
      ScrollController(keepScrollOffset: false);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('ScrollMetrics Demo'),
        ),
        floatingActionButton:
            Row(mainAxisAlignment: MainAxisAlignment.end, children: [
          FloatingActionButton(
            child: const Icon(Icons.add),
            onPressed: () => setState(() {
              itemCount += 1;
            }),
          ),
          const SizedBox(width: 20.0),
          FloatingActionButton(
            child: const Icon(Icons.remove),
            onPressed: () => setState(() {
              itemCount -= 1;
            }),
          ),
        ]),
        body: NotificationListener<ScrollMetricsNotification>(
          onNotification: (ScrollMetricsNotification notification) {
//             ScaffoldMessenger.of(notification.context).showSnackBar(
//               const SnackBar(
//                 content: Text('Scroll metrics changed!'),
//               ),
//             );

            print('Scroll metrics changed! itemCount = $itemCount ');

            return false;
          },
          child: Scrollbar(
            isAlwaysShown: true,
            child: ListView.builder(
              shrinkWrap: true,
              itemCount: itemCount,
              // 由外层 SingleChildScrollView 来控制滚动
              physics: const NeverScrollableScrollPhysics(),
              itemBuilder: (context, index) {
                return ListTile(
                  title: Text('Tile ${index+1}'),
                );
              },
            ),
          ),
        ),
      ),
    );
  }
}