Create a menu relative to a widget that shows and hides smoothly

menu_on_hover.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MaterialApp(home: Sample()));
}

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

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

class _SampleState extends State<Sample> {
  bool keepMenuVisible = false;
  GlobalKey buttonKey = GlobalKey();
  late OverlayEntry _overlayEntry;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance!.addPostFrameCallback((timeStamp) {
      _overlayEntry = _createOverlayEntry();
    });
  }

  OverlayEntry _createOverlayEntry() {
    final renderBox = buttonKey.currentContext!.findRenderObject() as RenderBox;
    var size = renderBox.size;
    var offset = renderBox.localToGlobal(Offset.zero);

    return OverlayEntry(
      builder: (_) => Positioned(
        left: offset.dx,
        top: offset.dy + size.height + 5.0,
        width: 200,
        child: MouseRegion(
          onEnter: (_) {
            keepMenuVisible = true;
          },
          onHover: (_) {
            keepMenuVisible = true;
          },
          onExit: (_) async {
            keepMenuVisible = false;
            clear();
          },
          child: Material(
            elevation: 4.0,
            child: ListView(
              padding: EdgeInsets.zero,
              shrinkWrap: true,
              children: <Widget>[
                ListTile(
                  onTap: () => print('tap action 1'),
                  title: Text('Action 1'),
                ),
                ListTile(
                  onTap: () => print('tap action 2'),
                  title: Text('Action 2'),
                )
              ],
            ),
          ),
        ),
      ),
    );
  }

  Future<void> clear() async {
    if (!keepMenuVisible) {
      await Future.delayed(Duration(milliseconds: 200));
      if (!keepMenuVisible) {
        _overlayEntry.remove();
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Stack(
          children: [
            MouseRegion(
              onEnter: (_) {
                Overlay.of(context)!.insert(_overlayEntry);
              },
              onExit: (_) => clear(),
              child: FloatingActionButton(
                key: buttonKey,
                onPressed: () {},
              ),
            ),
          ],
        ),
      ),
    );
  }
}