getter'uid'在null上被调用。

Question

我的应用程序流程如下：

包装程序->身份验证->登录

但是当我运行该应用程序时，它会显示红色屏幕和此异常：

    The following NoSuchMethodError was thrown building Wrapper(dirty, dependencies: [InheritedProvider<User>], state: _WrapperState#fd39b):
The getter 'uid' was called on null.
Receiver: null
Tried calling: uid

我以前曾经运行过它，并且运行良好，但我不为什么现在它会显示此异常：

这是主要的：

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return StreamProvider<User>.value(
      value: AuthService().user,
        child: MaterialApp(
          title: 'Sayarty',
          debugShowCheckedModeBanner: false,
          theme: ThemeData(
            primarySwatch: Colors.green,
            visualDensity: VisualDensity.adaptivePlatformDensity,
          ),
          home: Wrapper(),
        ),
    );
  }
}

这是包装器类：

    class Wrapper extends StatefulWidget {
  @override
  _WrapperState createState() => _WrapperState();
}

class _WrapperState extends State<Wrapper> {
  int _currentTab = 1;

  final _page = [
    Search(),
    Home(),
    Account(),
  ];

  @override
  Widget build(BuildContext context) {
    final user = Provider.of<User>(context);
    print(user.uid);

    if (user == null) {
      return Authenticate();
    } else {
      return
//        Home();
       }
}

Answer 1

可能是因为现在您在测试print(user.uid);之前添加了if user is == null

将其放入else：

//print(user.uid);

if (user == null) {
  return Authenticate();
} else {
  print(user.uid);
  return
    Home();
}