dispose() of Stateful widgets is not called when the App is exited by pressing the backbutton

Why are some widget state dispose() executed when the page is closed, some widget states don't execute dispose, it's really annoying, I want to cry, and the resource release is a problem.

It would be nice if you attach some problem code.

Because there is a lot of code, I can't paste it. I probably tested it myself. This happens when the current page is the last page of the application. Clicking Back will exit the application. At this time, the Widget and the Widget are included. The dispose() of all custom widgets is not executed. I wrote a demo that indicates what I want to express.

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: AppHomeWidget(),
    );
  }
}



class AppHomeWidget extends StatefulWidget{
  @override
  State<StatefulWidget> createState() {
    return AppHomeState();
  }
}

class AppHomeState extends State<AppHomeWidget>{

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      backgroundColor: Colors.white,
      body: Column(
        children: <Widget>[
          CustomWidget(),
          Text("text")
        ],
      ),
    );
  }

  @override
  void dispose() {
    super.dispose();
    print("AppHomeWidget dispose");
  }

}


class CustomWidget extends StatefulWidget{

  @override
  State<StatefulWidget> createState() {
    return SecondScreenState();
  }
}

class SecondScreenState extends State<StatefulWidget> {
  @override
  Widget build(BuildContext context) {
    return Center(
        child: new Text('CustomWidget')
    );
  }

  @override
  void dispose() {
    super.dispose();
    print("CustomWidget dispose");
  }
}

This demo has only one page. This page is also the last page of the application. In my actual project, it is the project's home page. Before it has a guide page, the login page is just that they have been closed. The home page is the end of the application. A page, similar to my demo, I don't know why, AppHomeWidget dispose and CustomWidget dispose are not printed.

In short, when the last page of the application is closed, all widgets' dispose() on this page will not be executed.

@dblokhin

@dblokhin Why the thumbs down if this code reproduces the problem?

@tvolkert

@tvolkert is this by design?

@escamoteur

@escamoteur the code was not fenced and highlighted. Currently it's nice. :)

I think this is a big problem. When I want to quit the application, I want to release some resources. Dispose() does not execute. I really don't know how to implement the resource shutdown. I think this problem should be faced by everyone. How to solve it? I want the answer, I am going crazy.

@HQiang

@HQiang What you can do use https://api.flutter.dev/flutter/widgets/WillPopScope-class.html
for this.

@escamoteur

@escamoteur Ok, thank you, rest on the weekend, I will try the company next Monday, thank you again, thank you

A question is why the state of CustomWidget extends State<StatefulWidget>. I wasn't able to check it but my guess is its the problem. I don't think it is a proper way to make a stateful widget.

Hey you have a sharp eye. It has to be State but I guess that's not really the problem because CustomWidget is a State full Widget. So this should only make problems when you try to access the widget from the state.
But I will give it a try.

I have not closely read this entire thread, but it seems like there are two main concerns here:

Cleaning up resources upon process exit.
Cleaning up resources when the Flutter engine is destroyed (perhaps including Dart VM shutdown), but the process (perhaps including the Dart VM) is still alive.

For the first case, I'm a bit at a loss. Any truly critical resources should just get cleaned up by the OS on process exit. If the resources you want to clean up are things like "send a network request" or "write to the file system," there's really no way to ensure the process can do that before being killed (the device has been powered off, the OS has killed you for memory pressure reasons, a privileged process has killed you with immediate effect, etc.).

For the second case, there are a number of ways to handle this already before you shut down the engine (for example, send a message to the process that would cause it to pump a new and empty widget tree).

I'd find it helpful to hear more about what kind of resources people need to clean up and why the current mechanisms aren't sufficient. For the first case, on platforms where it's well supported (namely desktop), WidgetsBindingObserver.didRequestAppExit can help with the first request (but only to a point, it will not be called e.g. if the power suddenly fails or the process is suddenly killed). For the second case, it's a little harder - but embedding Flutter into another application in general is a little bit harder.

My current situation is that the hybrid development of Flutter is only as part of the app. Click a button from the homepage to enter the Flutter map page. I need to call the dispose() method when closing flutter to tell the AndroidView to destroy the map, but the current mechanism has no way. callback received

Hey.
WTS?.
Still there?.

This is really hard to work around. I need to have a global registry of resources that I have to manually dispose because of this. It is mentioned in the documentation though, so I guess it's not a bug but correct - but very unexpected - behaviour.

What kind of resources do you have to dispose like that that isn't automatically disposed when the app terminates? Am 9. Sept. 2024, 19:03 +0100 schrieb Florian Wickert ***@***.***>:

…

This is really hard to work around. I need to have a global registry of resources that I have to manually dispose because of this. It is mentioned in the documentation though, so I guess it's not a bug but correct - but very unexpected - behaviour. — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you were mentioned.Message ID: ***@***.***>

In that particular case it's a thread that does some background rendering for a texture widget.

But why do you think you have to dispose that thread? Any thread created by the process will terminate when the process dies. Am 10. Sept. 2024, 07:18 +0100 schrieb Florian Wickert ***@***.***>:

…

In that particular case it's a thread that does some background rendering for a texture widget. — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you were mentioned.Message ID: ***@***.***>

In the end it will, but at least on Windows it does so with an abort message box.

Did you look into the NativeFinalizer class if you want to dispose a native Ressource for sure? Am 10. Sept. 2024, 07:52 +0100 schrieb Florian Wickert ***@***.***>:

…

In the end it will, but at least on Windows it does so with an abort message box. — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you were mentioned.Message ID: ***@***.***>

In the documentation for NativeFinalizer it reads:

This means NativeFinalizer can not be relied upon for running actions on the programs exit.

For now I can live with the error. There are workaround to get around this, it's just inconvenient.

@escamoteur

@escamoteur unfortunately, relying on NativeFinalizer is not portable (#132404) and is not triggered on Linux platform.

This needs some cleaning here in Flutter to have a standard way to release native resources on app exit (that is when Dart VM shutdown and before process exits) which is cross-platform and then clearly document this.

Any update on this ? This is a problem for me

fix: dispose widget tree on clean app exit (flutter#40940)

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dispose() of Stateful widgets is not called when the App is exited by pressing the backbutton #40940

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dblokhin commented on Sep 20, 2019

HQiang commented on Sep 20, 2019

HQiang commented on Sep 20, 2019

escamoteur commented on Sep 20, 2019

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dblokhin commented on Sep 20, 2019

HQiang commented on Sep 20, 2019

escamoteur commented on Sep 20, 2019

HQiang commented on Sep 20, 2019

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