dropdown_menu_scroll_position.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MaterialApp(
    home: Scaffold(
      appBar: AppBar(
        title: Text('DropdownButton'),
      ),
      body: Padding(
        padding: EdgeInsets.all(16.0),
        child: TestStatefulWidget(),
      ),
    ),
  ));
}

class TestStatefulWidget extends StatefulWidget {

  @override
  State<StatefulWidget> createState() => TestStatefulWidgetState();
}

class TestStatefulWidgetState extends State<TestStatefulWidget> {
  static const List<double> differentHeights = const [100, 200, 300, 400];
  double height = differentHeights[0];

  @override
  Widget build(BuildContext context) {
    return Column(
      crossAxisAlignment: CrossAxisAlignment.center,
      mainAxisAlignment: MainAxisAlignment.start,
      children: [
        Center(
          child: DropdownButton(
            value: height,
            itemHeight: null,
            onChanged: (newHeight) {
              setState(() {
                height = newHeight;
              });
            },
            items: differentHeights.map((height) {
              return DropdownMenuItem(
                value: height,
                child: Padding(
                  padding: const EdgeInsets.all(8.0),
                  child: Container(
                    color: Colors.blue,
                    height: height,
                    width: 100,
                    child: Center(child: Text('height: $height')),
                  ),
                ),
              );
            }).toList(),
          ),
        ),
      ],
    );
  }
}