异常：错误状态：无法获取 DocumentSnapshotPlatform 上不存在提供程序的字段

Question

我在 MyApp 上设置了提供程序流。

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final AuthService _auth = AuthService();
    String? _userId = _auth.user?.uid;
    return StreamProvider<UserProfileModel?>(
        initialData: null,
        create: (_) => DatabaseService().userProfileData(_userId),
        builder: (context, snapshot) {
          final userT = context.watch<UserProfileModel?>();
          final userType = userT?.userType;
          print('User type is: $userType');
          return MaterialApp(
            color: Colors.blueAccent,
            debugShowCheckedModeBanner: false,
            //home: TOCScreen(),
            home: _auth.user == null
                ? StartScreenMsg()
                : userType == 'Creditor'
                    ? CreditorHomePage()
                    : userType == 'Financial Recovery\nWorker'
                        ? FinancialHomePage()
                        : userType == 'Debtor'
                            ? DebtorHomePage()
                            : HomeScreen(),

这会从数据库中获取 userType 并相应地显示屏幕，它工作正常，但每当我运行应用程序时，它都会出现此异常。

════════ Exception caught by provider ══════════════════════════════════════════
The following assertion was thrown:
An exception was throw by _MapStream<DocumentSnapshot<Map<String, dynamic>>, UserProfileModel> listened by

StreamProvider<UserProfileModel?>, but no `catchError` was provided.

Exception:
Bad state: cannot get a field on a DocumentSnapshotPlatform which does not exist

════════════════════════════════════════════════════════════════════════════════

我认为这是因为开始时的 userId 为空，因此，它给出了这个异常。它不会导致崩溃或错误，但我不希望异常显示在调试控制台中。 这是 userProfileData 代码

Stream<UserProfileModel> userProfileData(String? user) {
    return _firestore
        .collection('users')
        .doc(user)
        .collection('userProfile')
        .doc(user)
        .snapshots()
        .map(_userProfileDataFromSnapshot);
  }

任何帮助将不胜感激。

Answer 1

如您上面提供的错误所示，这意味着 StreamProvider 具有名为 catchError 的属性，该属性是处理发出的错误并在发生错误时提供回退所必需的。

要捕获null，您可以检查以下示例中的方法。

StreamProvider(
  ...
  catchError: (_, __) => null,
  ...
)

您也可以参考此documentation 了解更多信息。