问我想从flutter应用程序启动WhatsApp应用程序

EN

import 'package:flutter/material.dart';
import 'package:url_launcher/url_launcher.dart';
import 'dart:io';


void main() => runApp(Wapp());

class Wapp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Demo',
      theme: ThemeData(
          primarySwatch: Colors.orange,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

final String title;

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

class _MyHomePageState extends State<MyHomePage> {
 void launchWhatsApp(
    {@required int phone,
    @required String message,
    }) async {
  String url() {
    if (Platform.isAndroid) {
      return "whatsapp://wa.me/$phone:03452121308:/?text=${Uri.parse(message)}";
    } else {
      return "whatsapp://send?   phone=$phone&text=${Uri.parse(message)}";
    }
  }

  if (await canLaunch(url())) {
    await launch(url());
  } else {
    throw 'Could not launch ${url()}';
  }
}


Widget build(BuildContext context){
  return Scaffold(
    appBar: AppBar(
      title: Text("Home"), 
    ),

  body: Center(
    child: RaisedButton(
      
      color: Colors.orange,
      textColor: Colors.black,
      padding: EdgeInsets.symmetric(vertical: 20.0, horizontal: 60.0),
      highlightColor: Colors.green,
      onPressed: () {
        launchWhatsApp(phone: 03452121308, message: 'Hello');
      },
      child: Text("Place Your Order",style: TextStyle(
          
          fontWeight: FontWeight.bold,
          fontSize: 15
          
        )
      )
    )
  )

  );
}

}