Gmail scroll button animation

main.dart

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


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


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

  @override
  State<GmailComposeButton> createState() => _GmailComposeButtonState();
}

class _GmailComposeButtonState extends State<GmailComposeButton> {
  // ScrollState scrollState = ScrollState.none;
  bool isButtonExpanded = true;

  final ScrollController _scrollController = ScrollController();

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
          appBar: AppBar(title: const Text("Gmail compose button")),
          body: NotificationListener<ScrollNotification>(
            onNotification: (ScrollNotification scrollInfo) {
              if (_scrollController.position.userScrollDirection ==
                  ScrollDirection.reverse) {
                if (isButtonExpanded == true) {
                  setState(() {
                    isButtonExpanded = false;
                  });
                }
              } else if (_scrollController.position.userScrollDirection ==
                  ScrollDirection.forward) {
                if (isButtonExpanded == false) {
                  setState(() {
                    isButtonExpanded = true;
                  });
                }
              } else if (_scrollController.position.userScrollDirection ==
                  ScrollDirection.idle) {}
              return true;
            },
            child: ListView.builder(
              controller: _scrollController,
              itemCount: 25,
              itemBuilder: (BuildContext content, int index) {
                return const ListTile(
                  leading: Icon(Icons.face),
                  title: Text(
                    "Your privacy is more important than ever",
                    maxLines: 1,
                  ),
                  subtitle: Text(
                    "With more and more of your personal information online — from banking and medical details to your physical location — it's more important than ever to protect yourself. (Don't believe us? Check out this episode of John Oliver's Last Week Tonight on data brokers.)",
                    maxLines: 1,
                  ),
                );
              },
            ),
          ),
          floatingActionButton: Container(
            padding: const EdgeInsets.symmetric(vertical: 13, horizontal: 15),
            decoration: const BoxDecoration(
              color: Colors.blueAccent,
              borderRadius: BorderRadius.all(
                Radius.circular(20),
              ),
            ),
            child: Row(
              mainAxisSize: MainAxisSize.min,
              crossAxisAlignment: CrossAxisAlignment.center,
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                const Icon(
                  Icons.edit,
                  color: Colors.white,
                ),
                AnimatedContainer(
                  padding: const EdgeInsets.only(left: 8),
                  duration: const Duration(milliseconds: 300),
                  width: isButtonExpanded ? 80 : 0,
                  child: const Text(
                    "Compose",
                    overflow: TextOverflow.clip,
                    maxLines: 1,
                    style: TextStyle(color: Colors.white),
                  ),
                ),
              ],
            ),
          ),
       ),
    );
  }
}