Dart Convert String To Double Float Using Flutter App

import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  String value1 = '87654321';
  double value2;
  changeType() {
    value2 = double.parse(value1);
    print(value2);
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
        home: Scaffold(
          appBar: AppBar(
            backgroundColor: Colors.deepOrange,
            title: Text('Custom New Widget'),
          ),
          body: Center(
              child: Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    Container(
                        margin: const EdgeInsets.fromLTRB(20, 10, 20, 10),
                        child: RaisedButton(
                          onPressed: () => changeType(),
                          child: Text('Convert String to Double on Click'),
                          textColor: Colors.white,
                          color: Colors.lightBlue,
                          padding: EdgeInsets.fromLTRB(12, 12, 12, 12),
                        )),
                  ])))
    );
  }
}