What is the scope of the snapshot of a StreamBuilder widget? - flutter

Question

I have a page with a column of TextFields. If I populate the TextFields with an existing record I do it through a TextEditingController for each field. I was passing in the QueryDocumentSnapshot from another page but I don't want to do that any longer because I am adding functionality where that no longer works. I can't use StreamProvider because I need some variables that are not available at the top of the tree in order to create the StreamProvider.
I think the best place to create the stream is in the page itself.
So now, I want to get the snapshot and initialize the TextEditingControllers in a method within the class and use them in the "build" method.
I don't know what the scope is of the snapshot that I create using StreamBuilder. How do I access the snapshot in another method in the class?
This is the column code in the build method:
Widget build(BuildContext context) {
return Scaffold(
body: SafeArea(
child: SingleChildScrollView(
reverse: true,
child: Padding(
padding: const EdgeInsets.all(20.0),
child: StreamBuilder(
stream: FirestoreService().getSingleAgencyTrxns(widget.trxnId),
builder: (context, trxnSnapshot) {
if (!trxnSnapshot.hasData) {
return Center(
child: CircularProgressIndicator(),
);
} else {
return Column(
children: <Widget>[
TextField(
autofocus: true,
keyboardType: TextInputType.text,
controller: clientFNameController,
textAlign: TextAlign.center,
onChanged: (value) {
trxnProvider.changeclientFName(value);
},
decoration: kTextFieldDecoration.copyWith(
hintText: 'Client First Name',
labelText: 'Client First Name'),
),
SizedBox(
height: 8.0,
),
TextField(
keyboardType: TextInputType.text,
controller: clientLNameController,
textAlign: TextAlign.center,
onChanged: (value) {
trxnProvider.changeclientLName(value);
},
decoration: kTextFieldDecoration.copyWith(
hintText: 'Client Last Name',
labelText: 'Client Last Name'),
),
SizedBox(
height: 8.0,
),
],
);
}
},
),
),
),
),
}
I initialize the TextEditingControllers through a method call in the initState method:
#override
void initState() {
getTrxn();
super.initState();
}
This is the getTrxn() method:
if (globals.currentTrxnId == null || globals.currentTrxnId == "") {
// new record: Set the textFields to blank
clientFNameController.text = "";
clientLNameController.text = "";
} else {
// Get the transaction
clientLNameController.text = someProvider?.clientLName ?? "";
clientTypeController.text = someProvider.clientType ?? "";
}
}

Answer 1

The snapshot variable is visible for every child widget, down from the builder property of the StreamBuilder.
This means that if you really need that info across your app you either:
Create a StreamBuilder on a top-ish level of your app;
Create several StreamBuilder across your app, which listen for the same events and behave accordingly.
The second option might be more complicated but I think that in some real-case scenarios it may be worth it: StreamBuilder re-builds its children when anything changes. Luckily, Flutter is smart enough to not re-build every element on the tree, but it still has to evaluate which Widget is marked as "dirty".