How to cancel StreamBuilder's assigned stream on navigating to different screen? - firebase

Question

Code:
final ref = Firestore.instance.document('some/path');
class MainPage extends StatefulWidget {
#override
_MainPageState createState() => _MainPageState();
}
class _MainPageState extends State<MainPage> {
Stream _stream;
#override
void initState() {
super.initState();
_stream = ref.snapshots().map((snapshot) {
// <--------------------------------------------------------------- line 1
return snapshot.data;
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: StreamBuilder(
stream: _stream,
builder: (_, snapshot) {
if (snapshot.hasData) {
return RaisedButton(
onPressed: () => Navigator.push(context, MaterialPageRoute(builder: (_) => Page2())),
child: Text("Navigate"),
);
}
return CircularProgressIndicator();
},
),
);
}
}
class Page2 extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
body: RaisedButton(
onPressed: () => ref.updateData({'key': "value"}), // <------ line 2
child: Text('Update data'),
),
);
}
}
This code is reproducible, no compile time error. Let me give you an overview.
There are 2 screen Screen1 and Screen2. On first screen, I have set up a StreamBuilder which listens for value provided using _stream. So far so good.
But when I navigate to Screen2 (see line 2), and update the server from it, the Screen1 snapshot gets built again (see line 1). How can I cancel that Stream so that I don't have to be worry about when Screen1 isn't in view?