Flutter 滚动监听 Demo

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

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


class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
          primarySwatch: Colors.blue, splashColor: Colors.transparent),
      home: HYHomePage(),
    );
  }
}

class HYHomePage extends StatefulWidget {
  @override
  _HYHomePageState createState() => _HYHomePageState();
}

class _HYHomePageState extends State<HYHomePage> {
  ScrollController _controller = ScrollController(initialScrollOffset: 300);
  bool _isShowFloatingBtn = false;

  @override
  void initState() {
    super.initState();
    _controller.addListener(() {
//      print("监听到滚动....: ${_controller.offset}");
      setState(() {
        _isShowFloatingBtn = _controller.offset >= 1000;
      });
    });

//    runCalc();
  }

  void runCalc() async {
    var result = await compute(calc, 100);
    print("---------: $result");
  }

  int calc(int count) {
    int total = 0;
    for (int i = 0; i < count; i++) {
      total += 0;
    }
    return total;
  }

  @override
  Widget build(BuildContext context) {
    /**
     * 两种方式可以监听:
     *  controller:
     *    1.可以设置默认值offset
     *    2.监听滚动, 也可以监听滚动的位置
     *  NotificationListener
     *    1.开始滚动和结束滚动
     */
    return Scaffold(
      appBar: AppBar(
        title: Text("列表测试"),
      ),
      body: NotificationListener(
        onNotification: (ScrollNotification notification) {
          if (notification is ScrollStartNotification) {
            print("开始滚动");
          } else if (notification is ScrollUpdateNotification) {
            print("正在滚动...,总滚动距离:${notification.metrics.maxScrollExtent} 当前滚动的位置: ${notification.metrics.pixels}");
          } else if (notification is ScrollEndNotification) {
            print("结束滚动");
          }
          return true;
        },
        child: ListView.builder(
            controller: _controller,
            itemCount: 100,
            itemBuilder: (BuildContext ctx, int index) {
              return ListTile(
                leading: Icon(Icons.people),
                title: Text("联系人$index"),
              );
            }
        ),
      ),
      floatingActionButton: _isShowFloatingBtn? FloatingActionButton(
        child: Icon(Icons.arrow_upward),
        onPressed: () {
          _controller.animateTo(0, duration: Duration(seconds: 1), curve: Curves.easeIn);
        },
      ): null,
    );
  }

  @override
  void dispose() {
    super.dispose();
    _controller.dispose();
  }
}