Drop down menu Flutter

import 'package:flutter/material.dart';
import 'package:tt/time_and_date_picker.dart';

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

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

class _DropDownBtnState extends State<DropDownBtn> {
  String dropdownValue = 'One';
  List<String> dropdownItem = ['One', 'Two', 'Three', 'Four'];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Dropdown Button"),
        centerTitle: true,
      ),
      body: Container(
        padding: EdgeInsets.all(10),
        margin: EdgeInsets.all(10),
        width: MediaQuery.of(context).size.width,
        color: Colors.white,
        child: DropdownButtonHideUnderline(
          child: DropdownButton<String>(
              value: dropdownValue,
              onChanged: (value){
                setState(() {
                  dropdownValue = value!;
                });
              },
              onTap: (){
                // Navigator.push(context, MaterialPageRoute(builder: (builder) => DateAndTimePicker()));
              },
              items: dropdownItem.map((String selectNumber) {
                return DropdownMenuItem(
                    value: selectNumber,
                    child: Text(
                      selectNumber,
                      style: TextStyle(color: Colors.amber),
                    ));
              }).toList()),
        ),
      ),
    );
  }
}