Flutter show's a red error screen before loading data from firebase using StreamBuilder, how to fix?

Question

I am getting data from firebase and making cards using that data. to display certain data of user from database, the data loads fine but for 1 second or more there is a red error screen. I want this to go away I'll show you my code. can somebody please help show me what's wrong. I have no clue what I am doing wrong that this happens and I get the error

The getter 'uid' was called on null. Receiver: null Tried calling: uid

The method '[]' was called on null. Receiver: null Tried calling:

here is my code, any help will be appreciated thankyou

class CardBuilder extends StatefulWidget {

  final String title;
  final String text;
  final IconData icon;

  CardBuilder({Key key, this.title,this.text,this.icon}): super(key: key);

  @override
  _CardBuilderState createState() => _CardBuilderState();
}

class _CardBuilderState extends State<CardBuilder> {
  FirebaseUser user;
  String error;

  void setUser(FirebaseUser user) {
    setState(() {
      this.user = user;
      this.error = null;
    });
  }

  void setError(e) {
    setState(() {
      this.user = null;
      this.error = e.toString();
    });
  }

  @override
  void initState() {
    super.initState();
    FirebaseAuth.instance.currentUser().then(setUser).catchError(setError);
  }

  @override
  Widget build(BuildContext context) {
    return StreamBuilder(
        stream: Firestore.instance.collection(UserInformation).document(user.uid).snapshots(),
        builder: (context, snapshot) {
          var userDocument = snapshot.data;
          // User userDocument here ..........
          return Card(
              margin: EdgeInsets.only(left: 20,right: 20,top: 20),
              child: ListTile(
                leading:
                Icon(widget.icon, color: QamaiGreen, size: 20.0),
                title: AutoSizeText(
                  '${widget.title} :   ${userDocument[widget.text]}',
                  style: TextStyle(
                      fontFamily: 'Montserrat',
                      fontWeight: FontWeight.w600,
                      color: QamaiThemeColor,
                      fontSize: 15
                  ),
                  maxLines: 1,
                  maxFontSize: 15,
                  minFontSize: 12,
                ),
              ));
        });
  }


} 

Answer 1

So after trying out some stuff I finally fixed this error. decided to post an answer since this question doesn't have any solution online. at-least I couldn't find one. hope this helps people having the same issue

what I first did was declare a String which contained the value of user.uid

String userid;
void _getUser() async {
  FirebaseUser user = await FirebaseAuth.instance.currentUser();
  userid=user.uid;
}

now in the card builder widget I got rid of the extra stuff and simply called _getUser() method in the init state

class _CardBuilderState extends State<CardBuilder> {

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

  @override
  Widget build(BuildContext context) {
    return StreamBuilder(
        stream: Firestore.instance.collection(UserInformation).document(userid).snapshots(),
        builder: (context, snapshot) {
          if(snapshot.hasData)
            {
              final userDocument = snapshot.data;
              final title=userDocument[widget.text];
              return Card(
                  margin: EdgeInsets.only(left: 20,right: 20,top: 20),
                  child: ListTile(
                    leading:
                    Icon(widget.icon, color: QamaiGreen, size: 20.0),
                    title: AutoSizeText(
                      '${widget.title} :   $title',
                      style: TextStyle(
                          fontFamily: 'Montserrat',
                          fontWeight: FontWeight.w600,
                          color: QamaiThemeColor,
                          fontSize: 15
                      ),
                      maxLines: 1,
                      overflow: TextOverflow.ellipsis,
                      maxFontSize: 15,
                      minFontSize: 9,
                    ),
                  ));
            }
          else{
            return Card(
                margin: EdgeInsets.only(left: 20,right: 20,top: 20),
                child: ListTile(
                  leading:
                  Icon(widget.icon, color: QamaiGreen, size: 20.0),
                  title: AutoSizeText(
                    'LOADING...',
                    style: TextStyle(
                        fontFamily: 'Montserrat',
                        fontWeight: FontWeight.w600,
                        color: QamaiThemeColor,
                        fontSize: 15
                    ),
                    maxLines: 1,
                    overflow: TextOverflow.ellipsis,
                    maxFontSize: 15,
                    minFontSize: 9,
                  ),
                ));
          }

        });
  }
}

Last changes were to add a condition checking if the snapshot has data or not. also saving the specific document field in a final variable helped a lot in my case that is

final title=userDocument[widget.text];

and finally an else condition was added to mimic the same card interface that shows a text which says loading. you can use CirculorIndicator if you want that will also work for me this was looking more natural for the interface.

Answer 2

you can show a progress indicator as your load your data as shown below

return StreamBuilder(
    stream: Firestore.instance.collection(UserInformation).document(user.uid).snapshots(),
    builder: (context, snapshot) {
    //==========show progress============
     if (!snapshot.hasData) {
        return CircularProgressIndicator()            
      }
      var userDocument = snapshot.data;
      // User userDocument here ..........

Answer 3

try this in main.dart:

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

Answer 4

When the device doesn't have proper internet connection or when the device is offline, flutter red error screen is displayed.

You can try using a CircularProgressIndicator as data loads from the API.

String userid;
void _getUser() async {
   FirebaseUser user = await FirebaseAuth.instance.currentUser();
   userid=user.uid;

}

Ensure you initialize the _getUser method.

  @override
  void initState() {
    getUser();
    super.initState();

}

You can now build your widget.

userid == null ? CircularProgressIndicator() : yourWidget(),