What Happened When I use the dispose with any Controller on Flutter?

Question

The questions is What happened when I call the .dispose() feature with any controller(For instance TextEditingController).

there is a example code at the below:

class SearchPage extends StatefulWidget {
  const SearchPage({Key? key}) : super(key: key);

  @override
  State<SearchPage> createState() => _SearchPageState();
}

class _SearchPageState extends State<SearchPage> {
  final TextEditingController _searchController = TextEditingController();
  @override
  void dispose() {
    // TODO: implement dispose
    super.dispose();
    _searchController.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text("Search Page"),
      ),
    );
  }
}

I have searched the internet but I couldn't find satisfaction answer.So,What happen, when I use the _searchController.dispose()?

Answer 1

As far as I remember this method is being called before it gets removed from the widget tree. Like a cleanup method. So after you disposed something you can't access it anymore and it will throw a error if you still try to access it.

Answer 2

• It checks if the object is still in use or not.
• check if listeners are null.

@mustCallSuper
void dispose() {
  assert(_debugAssertNotDisposed());
  assert(() {
    _debugDisposed = true;
    return true;
  }());
  _listeners = _emptyListeners;
  _count = 0;
}

Discards any resources used by the object. After this is called, the object is not in a usable state and should be discarded (calls to addListener will throw after the object is disposed)

Also try using super.dispos() on end part.

@override
  void dispose() {
    _searchController.dispose();
    super.dispose();
  }

State dispose

Called when this object is removed from the tree permanently.

Once you dispose of something, It is removed from the tree permanently.

You can check this question