Updating an object in Flutter is not working

Question

I try to update an object in Flutter from a child widget. The object which I want to update was passed as param to the child. The problem: The object does not want to change. I work on a Stateful widget and update the state with setState, but nothing changes. Maybe you can find an error in my code.

My object

final guestbook = Guestbook({
    title: "Test"
    // ... some other parameters
})

The function where I pass the Guestbook object to the child widget

void _editGuestbook(Guestbook guestbook, BuildContext context) {
  CupertinoScaffold.showCupertinoModalBottomSheet(
      context: context,
      builder: (BuildContext context, ScrollController scrollController) {
        return EditGuestbook(
          guestbook: guestbook, // Here I pass the object to the child
          scrollController: scrollController,
        );
      }).then((value) {
      setState(() {
        guestbook = value;
      });
  });
}

On the next widget, I update some values in the database and want to change also my local object, so that the user can see that the updating was successfull. Therefore I pass the object with the updated values as argument back to the parent view.

final Guestbook guestbook;
......
........

// Update database
final gb = widget.guestbook;
setState(() {
  updatedGuestbook = Guestbook(
      title: "New title",
      // ... some other parameters
});
await GuestbooksDatabase()
    .updateGuestbook(guestbook: updatedGuestbook, key: gb.id)
    .then((_) {
  Get.back(result: updatedGuestbook); // Here I send data back to parent
});

And as you can see above after retrieving the new object I update the state with setState:

setState(() {
  guestbook = value;
});

Bot nothing changes in the view. I always see the old state. If I pull to refresh to load the new entries directly from the database it updates. Is there a way to simply update the local object so that I don't need the additional server request?

Answer 1

The reason why the object using guestbook isn't updating after setState() is because guestbook was set to final. As of this writing, in Flutter 3.7.8 should give out a warning that the value can't be used as a setter since the value is final. You can either lazily initialize the variable with late or set a default value on the variable to get this working. See more detail here in the docs.