Flutter StreamBuilder returned null

Question

@override
  Widget build(BuildContext context) {

    final user = Provider.of<User>(context);

    return StreamProvider<QuerySnapshot>.value(   // irrelevant (?)
      value: DatabaseService().users,
      child: StreamBuilder<UserData>(
        stream: DatabaseService(uid: user.uid).userData,
        builder: (context, snapshot) {
          UserData userData = snapshot.data;
          if (!snapshot.hasData) {
            return ProfileSetup();
          } else {
            return Scaffold(...

I want to check if the user has already set up his profile by checking if there is any data of the user in the Firestore Cloud. Otherwise the user gets send to the setup page. The problem is that when there is finally the user data in the cloud I get an error message and a red screen for half a second, but after that it continues as it's suppost to. Yet I don't understand why there is an error message.

A build function returned null. The relevant error-causing widget was StreamBuilder< UserData>

Haroon Ashraf Awan · Accepted Answer · 2020-03-31 16:37:51Z

1

Use connectionstates in streambuilders. Try this:

@override
Widget build(BuildContext context) {

  final user = Provider.of<User>(context);

return StreamProvider<QuerySnapshot>.value(   // irrelevant (?)
   value: DatabaseService().users,
   child: StreamBuilder<UserData>(
   stream: DatabaseService(uid: user.uid).userData,
      builder: (context, snapshot) {
       UserData userData = snapshot.data;
       if (snapshot.hasData) {
       switch (snapshot.connectionState) {
       case ConnectionState.none:
                 return Text("No Connections");
       case ConnectionState.waiting:
                return CircularProgressIndicator();
       case ConnectionState.active:
       case ConnectionState.done:
         return snapshot.data.length > 0 ? ScaffoldPage() :ProfileSetup();
    default:
    break;
  }
  } 
          return Text("");

edited Mar 31, 2020 at 16:37

answered Mar 31, 2020 at 15:35

Haroon Ashraf Awan

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5 Comments

Vinzent Over a year ago

Unfortunately I still get the error. Also, (context, snapshot) is now underlined and says: This function has a return type of 'Widget', but doesn't end with a return statement. Try adding a return statement, or changing the return type to 'void'.

Vinoth Over a year ago

It means, you forgot to return widget for the builder function in some switch case @Vinzent

Haroon Ashraf Awan Over a year ago

I've edited my answer try this now. Replace else condition with return Text("") or SizedBox()

Vinzent Over a year ago

I just realised that I had else { return null; } at the next StreamBuilder and that was why I got the error... thank's a lot anyway!

Vinzent Over a year ago

But using the connection state helped me now to get rid of another problem so thank you :)

Amjad Khan · Accepted Answer · 2022-06-28 23:16:08Z

1

I am using firestore in my new project and has same problem

In my case I wasn't getting any error but snapshot has no data so I did checked

if (snapshot.hasError) return Text('error ${snapshot.error}');

which helped me see what's error and it was because index wasn't enable

answered Jun 28, 2022 at 23:16

Amjad Khan

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