Data not store in List variable while use stream builder

Question

when I used Firestore query data stored in list variable but when I try to use this data outside the query it won't work. Please help me where I'm making mistake.

 List<ContactsModelClass> _groupContactList1 ; //declare list variable 
                  _groupCollection
                      .doc(widget.groupId)
                      .collection("groupContactList")
                      .get()
                      .then((docs) {
                    showLog('--->>>>>>${docs.docs.length}');
                    _groupContactList1 = List<ContactsModelClass>.generate(
                      docs.docs.length,
                      (index) => ContactsModelClass.fromJson(
                        docs.docs[index].data(),
                      ),
                    );  //Store data in list variable
                    print("init groupList:[${_groupContactList1.length}]"); //get data 
                  });                   
                  print(
                      "groupContactList list data:[${_groupContactList1.length}]"); // can not access data which store above in code. why?

聂超群 · Accepted Answer · 2021-12-08 07:02:41Z

2

Because then callback is called later, where you set your _groupContactList1 . But you print _groupContactList1.lenght now, which is not set yet.

Use await instead, try solution below:

var docs = await _groupCollection.doc(widget.groupId).collection("groupContactList").get();
showLog('--->>>>>>${docs.docs.length}');
_groupContactList1 = List<ContactsModelClass>.generate(
 docs.docs.length,
 (index) => ContactsModelClass.fromJson(docs.docs[index].data()),
);
print("groupContactList list data:[${_groupContactList1.length}]");

answered Dec 8, 2021 at 7:02

聂超群

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Kuntec · Accepted Answer · 2021-12-08 07:01:41Z

1

You need to put the await keyword for the fetching of docs from the Firestore. Once Firestore fetches the data then display or use the list.

answered Dec 8, 2021 at 7:01

Kuntec

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