data in StreamBuilder keeps returning null outside of Firebase RTDB get() call

Question

For some reason, my data variable keeps returning null outside of my .get() call. Within the .get() call, when I print data, I get the expected map. Any insight is appreciated! The part of the code that is giving me issues are in asterisks.

class _MessagesScreenState extends State<MessagesScreen> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Column(
          children: <Widget>[
            Expanded(
              child: Container(
                decoration: BoxDecoration(
                  color: Colors.white,
                ),
                child: StreamBuilder(
                    stream: rtdb
                        .child('messages')
                        .child(widget.currentUserID)
                        .onValue,
                    builder: (context, snapshot) {
                      final messageList = <BuildMessages>[];
                      if (snapshot.hasData) {
                        final users = Map<String, dynamic>.from(
                            snapshot.data.snapshot.value);
                        users.forEach((key, value) {
                          **var data;**
                          **usersRef.child(key).get().then((value) {
                            data = new Map<String, dynamic>.from(value.value);
                          });**
                          final messageTile = BuildMessages(
                            name: data['userFirstName'] +
                                ' ' +
                                data['userLastName'],
                            picture: data['userImageUrl'],
                            otherID: data['userID'],
                          );
                          ;
                          messageList.add(messageTile);
                        });
                      }
                      return ListView.builder(
                        padding: EdgeInsets.only(top: 15.0),
                        itemCount: messageList.length,
                        itemBuilder: (context, index) {
                          return messageList[index];
                        },
                      );
                    }),
              ),
            ),
          ],
        ),
    );
  }

Hey there! Yes your answer was very helpful. Thanks Frank – ckingprogramming Aug 08 '21 at 17:20 — ckingprogramming, Aug 08 '21 at 17:20

score 1 · Accepted Answer · answered Aug 01 '21 at 21:00

That is the expected behavior. The usersRef.child(key).get() returns a Future<DataSnapshot?>, so you'll need to wrap it into a FutureBuilder to use its value.

Based on this answer that'd be something like:

FutureBuilder<DataSnapshot?>(
  future: usersRef.child(key).get(), // async work
  builder: (BuildContext context, AsyncSnapshot<DataSnapshot?> snapshot) {
    switch (snapshot.connectionState) {
      case ConnectionState.waiting: return Text('Loading....');
      default:
        if (snapshot.hasError)
          return Text('Error: ${snapshot.error}');
        else
          return Text('Result: ${snapshot.data!.value}');
    }
  },
)

data in StreamBuilder keeps returning null outside of Firebase RTDB get() call

1 Answers1