In Flutter show a Drop Down for Android and a Picker for iOS

nativepicker.dart

import 'dart:io';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:my_unify_mobile/custom/native_widgets.dart';

class ExamplePickerPage extends StatefulWidget {
  @override
  ExamplePickerPageState createState() => ExamplePickerPageState();
}

class ExamplePickerPageState extends State<ExamplePickerPage> {
  double _kPickerSheetHeight = 216.0;
  double _kPickerItemHeight = 32.0;

  int _index = 0;
  List<String> _items = ['Test', 'Example', 'Demo'];
  String selection = "";

  bool _isDarkTheme = false;
  double _fontSize = 14.0;

  Widget _buildNativePicker() {
    final FixedExtentScrollController scrollController =
        new FixedExtentScrollController(initialItem: _index);
    return Platform.isIOS
        ? new Container(
            height: _kPickerSheetHeight,
            color: CupertinoColors.white,
            child: new DefaultTextStyle(
              style: const TextStyle(
                color: CupertinoColors.black,
                fontSize: 22.0,
              ),
              child: new GestureDetector(
                // Blocks taps from propagating to the modal sheet and popping.
                onTap: () {},
                child: new SafeArea(
                  child: new CupertinoPicker(
                    scrollController: scrollController,
                    itemExtent: _kPickerItemHeight,
                    backgroundColor: CupertinoColors.white,
                    onSelectedItemChanged: (int index) {
                      setState(() {
                        _index = index;
                        selection = _items[_index];
                      });
                    },
                    children:
                        new List<Widget>.generate(_items.length, (int index) {
                      return new Center(
                          child: new Text(
                        _items[index],
                        style:
                            TextStyle(fontSize: _fontSize, color: Colors.black),
                      ));
                    }),
                  ),
                ),
              ),
            ),
          )
        :  DropdownButton<String>(
                  value: selection,
                  items: _items
                      .map(
                        (String item) => DropdownMenuItem<String>(
                            value: item,
                            child: SizedBox(
                                width: 200.0,
                                child: Text(
                                  item,
                                  style: TextStyle(
                                      fontSize: _fontSize,
                                      color: _isDarkTheme
                                          ? Colors.white
                                          : Colors.black),
                                ))),
                      )
                      .toList(),
                  onChanged: (s) {
                    setState(() {
                      selection = s;
                    });
                  });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: ListTile(
      leading: Icon(Icons.info),
      title: const Text('Select a Result'),
      subtitle: Platform.isIOS
          ? Text(
              selection,
              style: TextStyle(
                  fontSize: _fontSize,
                  color: _isDarkTheme ? Colors.white : Colors.black),
            )
          : _buildNativePicker(),
      trailing: _items.length == 1 ? NativeLoadingIndicator() : Text(''),
      onTap: !Platform.isIOS
          ? null
          : () async {
              await showModalBottomSheet<void>(
                context: context,
                builder: (BuildContext context) {
                  return _buildNativePicker();
                },
              );
            },
    ));
  }
}