我是一个初学者在一个Flutter，我已经创建了我的应用程序，但我想检查如果用户打开应用程序后第一次安装，我已经看到this article但不知道如何？
这是启动屏幕代码，代码在3秒后将用户直接移动到主屏幕，但我想检查用户是否首次打开应用程序并将用户移动到欢迎屏幕，或者如果用户不是首次打开应用程序并将用户移动到主屏幕。

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:book_pen/main.dart';
import 'package:book_pen/Welcome.dart';

void main() {
  runApp(new MaterialApp(
    home: new SplashScreen(),
    routes: <String, WidgetBuilder>{
      '/HomePage': (BuildContext context) => new HomePage(),
      '/WelcomePage': (BuildContext context) => new WelcomePage()
    },
  ));
}

class SplashScreen extends StatefulWidget {
  @override
  _SplashScreenState createState() => new _SplashScreenState();
}

class _SplashScreenState extends State<SplashScreen> {
  startTime() async {
    var _duration = new Duration(seconds: 3);

    return new Timer(_duration, navigationPageHome);
  }

  void navigationPageHome() {
    Navigator.of(context).pushReplacementNamed('/HomePage');
  }

  void navigationPageWel() {
    Navigator.of(context).pushReplacementNamed('/WelcomePage');
  }

  @override
  void initState() {
    super.initState();
    startTime();
  }

@override
  Widget build(BuildContext context) {
    Size size = MediaQuery.of(context).size;
    return Scaffold(
      body: Stack(
        children: <Widget>[
          Center(
            child: new Image.asset(
              'assets/images/SplashBack.jpg',
              width: size.width,
              height: size.height,
              fit: BoxFit.fill,
            ),
          ),
          Center(
              child: new Image.asset(
            'assets/images/BigPurppleSecSh.png',
            height: 150,
            width: 300,
          )),
        ],
      ),
    );
  }
}