Dropdown example

import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: MyDropDown()
    );
  }
}

class MyDropDown extends StatefulWidget {
  @override
  _MyDropDownState createState() => _MyDropDownState();
}

class _MyDropDownState extends State<MyDropDown> {
  final List<String> subjects = ["Computer Science", "Biology", "Math"];

  String selectedSubject = "Biology";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        width: double.infinity,
        height: double.infinity,
        padding: EdgeInsets.all(32),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.center,
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            DropdownButton<String>(
              value: selectedSubject,
              onChanged: (value){
                setState(() {
                  selectedSubject = value;
                });
              },
              items: subjects.map<DropdownMenuItem<String>>((value){
                return DropdownMenuItem(
                  child: Text(value),
                  value: value,
                );
              }).toList(),
            ),

            Text(selectedSubject, style: TextStyle(fontSize: 36, fontWeight: FontWeight.w900),)

          ],
        ),
      ),
    );
  }
}