I have two screens in my app.
Screen A runs a computationally expensive operation while opened, and properly disposes by cancelling animations/subscriptions to the database when dispose()
is called to prevent memory leaks.
From Screen A, you can open another screen (Screen B).
When I use Navigator.pushNamed
, Screen A remains in memory, and dispose()
is not called, even though Screen B is now shown.
Is there a way to force disposal of Screen A when it is not in view?
Example code where first route is never disposed:
import 'package:flutter/material.dart';
void main() {
runApp(MaterialApp(
title: 'Navigation Basics',
home: FirstRoute(),
));
}
class FirstRoute extends StatefulWidget {
@override
_FirstRouteState createState() => _FirstRouteState();
}
class _FirstRouteState extends State<FirstRoute> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('First Route'),
),
body: RaisedButton(
child: Text('Open route'),
onPressed: () {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => SecondRoute()),
);
},
),
);
}
@override
void dispose() {
// Never called
print("Disposing first route");
super.dispose();
}
}
class SecondRoute extends StatefulWidget {
@override
_SecondRouteState createState() => _SecondRouteState();
}
class _SecondRouteState extends State<SecondRoute> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Second Route"),
),
body: RaisedButton(
onPressed: () {
Navigator.pop(context);
},
child: Text('Go back!'),
),
);
}
@override
void dispose() {
print("Disposing second route");
super.dispose();
}
}
I know it's a bit late but I think you should override the deactivate
method. Since we are changing the page we are not actually destroying it, that's why the dispose
isn't being called.
If you'd like more information this page lists the lifecycle of the stateful widgets.
From the link:
'deactivate()' is called when State is removed from the tree, but it might be reinserted before the current frame change is finished. This method exists basically because State objects can be moved from one point in a tree to another.
call Navigator.pushReplacement
when routing between first and second screen.
import 'package:flutter/material.dart';
void main() {
runApp(MaterialApp(
title: 'Navigation Basics',
home: FirstRoute(),
));
}
class FirstRoute extends StatefulWidget {
@override
_FirstRouteState createState() => _FirstRouteState();
}
class _FirstRouteState extends State<FirstRoute> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('First Route'),
),
body: RaisedButton(
child: Text('Open route'),
onPressed: () {
Navigator.pushReplacement(
context,
MaterialPageRoute(builder: (context) => SecondRoute()),
);
},
),
);
}
@override
void dispose() {
// Never called
print("Disposing first route");
super.dispose();
}
}
class SecondRoute extends StatefulWidget {
@override
_SecondRouteState createState() => _SecondRouteState();
}
class _SecondRouteState extends State<SecondRoute> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Second Route"),
),
body: RaisedButton(
onPressed: () {
Navigator.pushReplacement(
context,
MaterialPageRoute(builder: (context) => FirstRoute()),
);
},
child: Text('Go back!'),
),
);
}
@override
void dispose() {
print("Disposing second route");
super.dispose();
}
}
Try this
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