在 main.dart 中使用 FutureBuilder

Question

下面的代码总是显示 OnboardingScreen 一段时间（可能是几毫秒），然后显示 MyHomePage。我相信你们都明白我想做什么。我正在使用 FutureBuilder 来检查 getString 方法是否有数据。我有什么错？或者还有其他最好的方法吗？

saveString() async {
  final prefs = await SharedPreferences.getInstance();
  prefs.setString('firstOpen', '1');
}

getString() 方法始终返回字符串。

getString() async {
  final prefs = await SharedPreferences.getInstance();
  String txt = prefs.getString('firstOpen');
  return txt;
}

主程序.dart

home: new FutureBuilder(
            future: getString(),
            builder: (context, snapshot) {
              if (snapshot.hasData) {
                return MyHomePage();
              } else {
                return OnboardingScreen();
              }
            })

Answer 1

通常我使用另一条路线，而不是 FutureBuilder。因为futurebuilder每次热重载都会重置futureBuilder。

数据加载之前总会有一些延迟，因此您需要在数据加载之前显示一些内容。

Snapshot.hasData 仅显示已解决的未来的返回数据。

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(primarySwatch: Colors.blue),
      home: SplashScreen(),
    );
  }
}

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

const isOnboardingFinished = 'isOnboardingFinished';

class _SplashScreenState extends State<SplashScreen> {
  Timer timer;
  bool isLoading = true;

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

  Future<void> _checkIfFirstOpen() async {
    final prefs = await SharedPreferences.getInstance();
    var hasOpened = prefs.getBool(isOnboardingFinished) ?? false;

    if (hasOpened) {
      _changePage();
    } else {
      setState(() {
        isLoading = false;
      });
    }
  }

  _changePage() {
    Navigator.of(context).pushReplacement(
      // this is route builder without any animation
      PageRouteBuilder(
        pageBuilder: (context, animation1, animation2) => HomePage(),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return isLoading ? Container() : OnBoarding();
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(child: Text('homePage'));
  }
}

class OnBoarding extends StatelessWidget {
  Future<void> handleClose(BuildContext context) async {
    final prefs = await SharedPreferences.getInstance();
    prefs.setBool(isOnboardingFinished, true);
    Navigator.of(context).pushReplacement(
      MaterialPageRoute(
        builder: (_) => HomePage(),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Center(
        child: RaisedButton(
          onPressed: () => handleClose(context),
          child: Text('finish on bording and never show again'),
        ),
      ),
    );
  }
}