import 'package:flutter_web/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,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  Widget build(BuildContext context) {
    // This works fine if it is set to the default value of 48
    final double itemHeight = 20;

    List<PopupMenuItem<int>> dropDownItems = List<PopupMenuItem<int>>();
    for(int i = 0; i < 10; ++i) {
      dropDownItems.add(PopupMenuItem<int>(
        height:itemHeight,
        value:0, 
        child:SizedBox(
          child:Text(i.toString()), 
          height:itemHeight)
      ),);
    }

    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            GestureDetector(
              child:Text('Click me'),
              onTapDown:(TapDownDetails tapDownDetails) async {
                await showMenu<int>(
                  context: context,
                  initialValue: 0,
                  position: RelativeRect.fromLTRB(
                    tapDownDetails.globalPosition.dx, 
                    tapDownDetails.globalPosition.dy, 
                    tapDownDetails.globalPosition.dx + 100, 
                    tapDownDetails.globalPosition.dx + 100),
                  items: dropDownItems,
                );
              },
            ),
          ],
        ),
      ),
    );
  }
}