RadioListTile -> radio button not updating state

Question

In a stateful widget, all radios are in a Dialog widget :

class YourState extends State<YourWidget> {
Item _item;
@override
Widget build(context){
  if (_item == null) {
    _item = itemList[0]; //data set up just before
  } *(1)*
  List<Widget> childs = [];

  childs.add(
        Container(
            child: Material(
                child: RadioListTile<Area>(
          activeColor: appPrimaryColor,
          title: Text(item.name.toString()),
          value: item,
          selected: item == _item,
          groupValue: _item,
          onChanged: (Item value) {
            if (value != null) {
              setState(() => _item = value);
              print(_item == value);
              print(_item);
            }
          },
        ))),
      );
  }
}

So here is my problem, the radiobutton state is not updating when tapped. When I open the dialog it does show that my selection to first item is working (1), but it doesn't change to selected when tapped. The prints does return true and _item value has the right value.

Answer 1

You should keep Item _item; in class properties.

class YourState extends State<YourWidget> {
  Item? _item;//Declare here
  
  @override
  Widget build(context){
    if (_item == null) {
      _item = itemList[0]; //data set up just on initial
    } 
    List<Widget> childs = [];

    childs.add(
        Container(
            child: Material(
                child: RadioListTile<Area>(
          activeColor: appPrimaryColor,
          title: Text(item.name.toString()),
          value: item,
          selected: item == _item,
          groupValue: _item,
          onChanged: (Item value) {
            if (value != null) {
              setState(() => _item = value);
              print(_item == value);
              print(_item);
            }
          },
        ))),
      );
     ...
  }
}

Edited

Following code is working for me..

class YourWidget extends StatefulWidget {
  const YourWidget({super.key});

  @override
  State<YourWidget> createState() => _YourWidgetState();
}

class _YourWidgetState extends State<YourWidget> {
  List<Area> items = List.generate(6, (index) => Area('Name: $index'));
  Area? _item;

  @override
  Widget build(BuildContext context) {
    _item ??= items[0];
    return ListView.builder(
      itemCount: items.length,
      physics: const BouncingScrollPhysics(),
      itemBuilder: (context, int i) {
        final item = items[i];
        return RadioListTile<Area>(
          activeColor: Colors.teal,
          title: Text(item.name.toString()),
          value: item,
          selected: item == _item,
          groupValue: _item,
          onChanged: (Area? value) {
            if (value != null) {
              setState(() => _item = value);
              print(_item == value);
              print(_item);
            }
          },
        );
      },
    );
  }
}

class Area {
  final String name;

  Area(this.name);
}