Flutter QuerySnapshot return null - firebase

Question

What I really want to do is take all the ORDER IDs ("order_id") that are in the "deliver" collection and use these IDs in another call, that is, enter in "orders" collection and inform all IDs I got in the "deliver" collection as documents.
my stream:
function() {
Firestore.instance
.collection("delivers")
.document("fvRpb1xDOKejJ5AEqXEeThaqhci1")
.collection("orders")
.snapshots()
.listen((orders) {
orders.documents.forEach((f) {
print("+++++ First +++++ ${f.data}");
Firestore.instance
.collection("orders")
.document(f.documentID)
.snapshots();
});
});
}
My StreamBuilder Bellow:
body: Container(
child: StreamBuilder<QuerySnapshot>(
stream: function(),
builder: (context, AsyncSnapshot<QuerySnapshot> snapshot) {
print("SNAPSHOT DATA ++++++ ${snapshot.toString()} ++++++}");
// if (snapshot.hasError)
// print("ERRO EM ++++++ ${snapshot.error.toString()} ++++++}");
if (!snapshot.hasData)
return Center(
child: RaisedButton(
onPressed: function, child: Text("press")));
switch (snapshot.connectionState) {
case ConnectionState.waiting:
return circularProgress();
break;
default:
print(
"CONNECTION DEFAULT ++++++ ${snapshot.toString()} ++++++}");
return ListView(
children: snapshot.data.documents
.map((DocumentSnapshot myOrder) {
return Text(myOrder["quantity"]);
}).toList());
}
}),
),
RETURNS:
I/flutter ( 600): +++++ First +++++ {order_id: 2tC5gbAYLoj375w9HrKc}
Performing hot reload... ⡿I/flutter ( 600): SNAPSHOT DATA ++++++ AsyncSnapshot(ConnectionState.none, null, null) ++++++}
my firestore screen shots
https://drive.google.com/drive/u/0/folders/1ZeXog80wvnR-6cTG2VCE0jOVfrSEyDaM

Answer 1

You are not returning anything from function().
Add return keyword before snapshots as :
return Firestore.instance
.collection("delivers")
.document("fvRpb1xDOKejJ5AEqXEeThaqhci1")
.collection("orders")
.snapshots();
or simply put the snapshot in front of the stream, as :
stream:Firestore.instance.collection('delivers').document('fvRpb1xDOKejJ5AEqXEeThaqhci1')____________.snapshots(),

Answer 2

I share a possible cause of problem of: "ALWAYS having null on snapshots results even the data is there in Firebase"
It might be your cloud_firestore version in pubspec.yaml caused the problem. I tried different methods of fetching data on Youtube, but none of them worked, I finally changed the version of cloud_firestore from ^0.14.4 to ^0.13.5, and the data suddenly all appeared! Here is my specific version changes in pubspec.yaml: the commented are the new version that does not work.
# cloud_firestore: ^0.14.4
cloud_firestore: ^0.13.5
firebase: ^7.3.3
# firebase_auth: ^0.18.4+1
firebase_auth: ^0.15.4
# firebase_core: ^0.5.3
firebase_core: ^0.4.4
This might not be the cause of your problem, but it may help some others :D