布尔表达式不能为null？ [英] Boolean expression must not be null?

问题描述

有人知道我为什么得到Failed断言：布尔表达式不能为null。
如果我已经登录并退出该应用程序，然后再次打开该应用程序，则应该直接在主屏幕中。

Does anyone know why i got the Failed assertion: boolean expression must not be null. If I had logged in and quit the app and open the app again i should be directly in the homescreen.

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

class MyApp extends StatefulWidget {

  // This widget is the root of your application.
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {

  bool userIsLoggedIn = false;

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

  getLoggedInState()async{
    await HelperFunction.getUserLoggedInSharedPreference().then((value){
      setState(() {
        userIsLoggedIn = value;
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: userIsLoggedIn ? HomeScreen() : CompanyLoadingBar(),
    );
  }
}

推荐答案

如果您的值在此处可能为空-您会收到错误消息。
为了安全起见，将setState内的行更改为：

If your 'value' here can become null - you get the error. To be safe change the line inside setState to:

userIsLoggedIn = value ?? false; 

如果值为null，它将布尔值设置为false

it will set the bool to false if value is null

这篇关于布尔表达式不能为null？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！