How To Use Array Key Value Pair In Flutter Dropdown Button

import 'package:flutter/material.dart';

void main(){
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List<KeyValueModel> _datas = [
    KeyValueModel(key: "Key 1", value: "Value 1"),
    KeyValueModel(key: "Key 2", value: "Value 2"),
    KeyValueModel(key: "Key 3", value: "Value 3"),
    KeyValueModel(key: "Key 4", value: "Value 4"),
    KeyValueModel(key: "Key 5", value: "Value 5"),
  ];

  String _selectedValue = "";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.orange[800],
        title: Text('Key value Pair - DropdownButton'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          mainAxisSize: MainAxisSize.max,
          children: <Widget>[
            DropdownButton<String>(
              items: _datas
                  .map((data) => DropdownMenuItem<String>(
                child: Text(data.key),
                value: data.value,
              ))
                  .toList(),
              onChanged: (String value) {
                setState(() => _selectedValue = value);
              },
              hint: Text('Select Key'),
            ),
            SizedBox(
              height: 25.0,
            ),
            Text(_selectedValue),
          ],
        ),
      ),
    );
  }
}

class KeyValueModel {
  String key;
  String value;

  KeyValueModel({this.key, this.value});
}