Flutter popped screen retains values when called again - flutter

Question

I have a ScreenA with 2 buttons. Button 1 pushes ScreenB(snapshot) and is received as ScreenB(this.snapshot). Button 2 pushes ScreenB(null). Depending on wether snapshot is null or not in ScreenB, different methods are triggered in ScreenB initState.
Now, If I first press Button 2, i.e. ScreenB(null), snapshot is indeed null in ScreenB. But If I press Button1, i.e. ScreenB(snapshot), then pop ScreenB, then press Button2, I would expect snapshot to be null in ScreenB, but it's not.
Am I missing something here? Appreciate some enlightment.
Test Code added as requested:
ScreenA:
import 'screen_b.dart';
import "package:flutter/material.dart";
import 'mock_data.dart';
List < MockData > snapshot = List < MockData > ();
class ScreenA extends StatelessWidget {
#override
Widget build(BuildContext context) {
snapshot.add(MockData("1", "title", "description"));
return Scaffold(
appBar: AppBar(
title: Text("ScreenA"),
centerTitle: true,
),
body: Padding(
padding: const EdgeInsets.all(12.0),
child: ListView(
children: < Widget > [
Center(child: FlatButton(
child: Text("Goto ScreenB with null", style: TextStyle(fontSize: 20.0, color: Colors.blue)),
onPressed: () {
Navigator.of(context).push(
MaterialPageRoute(builder: (context) => ScreenB(null)));
},
), ),
SizedBox(height: 20.0), Center(child: FlatButton(
child: Text("Goto ScreenB with data", style: TextStyle(fontSize: 20.0, color: Colors.blue)),
onPressed: () {
Navigator.of(context).push(
MaterialPageRoute(builder: (context) => ScreenB(snapshot[0])));
},
), ),
],
),
), );
}
}
ScreenB:
import "package:flutter/material.dart";
import 'mock_data.dart';
bool editing = false;
class ScreenB extends StatefulWidget {
ScreenB(this._snapshot);
final MockData _snapshot;
#override
_ScreenBState createState() => _ScreenBState();
}
class _ScreenBState extends State < ScreenB > {
#override
void initState() {
super.initState();
if (widget._snapshot != null) {
editing = true;
}
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("ScreenB"),
centerTitle: true,
),
body: Padding(
padding: const EdgeInsets.all(30.0),
child: Center(child: Text("Is Editing: $editing ",
style: TextStyle(fontSize: 20.0, color: Colors.red)),
),
), );
}
}
MockData Class:
class MockData {
String id;
String title;
String description;
MockData(this.id, this.title, this.description);
}
To test:
1. run ScreenA and tap button "Goto ScreenB with null". Text on ScreenB shows "Is Editing: false" as expected.
Hit back arrow on appBar to pop ScreenB, then tap "Goto ScreenB with data". Text on ScreenB shows "Is Editing: true" as expected.
Repeat 1 and now Text on ScreenB shows "Is Editing: true" as NOT expected.

Answer 1

Is the snaphot that you mentioned here of type AsyncSnapshot , if yes then the data snapshot is never null, the data field of snapshot is what is null
snapshot.data == null
Let me know if this helps.

Answer 2

Ended up doing:
#override
void dispose() {
editing = false;
super.dispose();
}
in ScreenB. Still puzzled though why the variable keeps the last value, even after the screen has been popped.