Flutter Demo, ScrollController Example: addListener and animateTo

main.dart

import 'package:flutter/material.dart';

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

class ScrollControllerTest extends StatefulWidget {
  final String title;
  const ScrollControllerTest({super.key, required this.title});

  @override
  State<ScrollControllerTest> createState() => _ScrollControllerTestState();
}

class _ScrollControllerTestState extends State<ScrollControllerTest> {
  ScrollController controller = ScrollController();
  bool showtoTopBtn = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(widget.title)),
      body: Scrollbar(
          controller: controller,
          child: ListView.builder(
              itemCount: 100,
              itemExtent: 50.0,
              controller: controller,
              itemBuilder: ((context, index) => ListTile(
                    title: Text("$index"),
                  )))),
      floatingActionButton: !showtoTopBtn
          ? null
          : FloatingActionButton(
              onPressed: (() {
                controller.animateTo(.0,
                    duration: const Duration(seconds: 2), curve: Curves.ease);
              }),
              child: const Icon(Icons.arrow_upward),
            ),
    );
  }

  @override
  void initState() {
    super.initState();
    controller.addListener(() {
      print(controller.offset);
      if (controller.offset < 1000 && showtoTopBtn) {
        setState(() {
          showtoTopBtn = false;
        });
      } else if (controller.offset >= 1000 && !showtoTopBtn) {
        setState(() {
          showtoTopBtn = true;
        });
      }
    });
  }

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const ScrollControllerTest(
          title: 'ScrollController Example: addListener and animateTo'),
    );
  }
}