How to deselect the already selected item after tap on another item ListView in Flutter?

Question

I would like to allow user to select only one option from the list, if he select one after another, then only last option should be considered as selected.

In current code, user can select multiple option from the list which i want to avoid.

Tried code:

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Test App',
      theme: new ThemeData(
        primarySwatch: Colors.red,
      ),
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List<int> indexList = new List();
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Selected ${indexList.length}  ' + indexList.toString()),
      ),
      body: new ListView.builder(
        itemCount: 3,    
        itemBuilder: (context, index) {
          return new CustomWidget(  
            index: index,
            callback: () {
              if (indexList.isNotEmpty) {
                indexList.clear();
              } 

            },
          );
        },
      ),
    );
  }
}

class CustomWidget extends StatefulWidget {
  final int index;
  final VoidCallback callback;

  const CustomWidget({Key key, this.index, this.callback}) : super(key: key);

  @override
  _CustomWidgetState createState() => new _CustomWidgetState();
}


class _CustomWidgetState extends State<CustomWidget> {
  bool selected = false;
  CustomWidget lastSelectedWidget;

  @override
  Widget build(BuildContext context) {
    return new GestureDetector(
      onTap: () {
          setState(() {
            lastSelectedWidget = widget;
            print(lastSelectedWidget.key);
            selected = !selected;
          });
          widget.callback();
      },
      child: new Container(
        margin: new EdgeInsets.all(5.0),
        child: new ListTile(
          title: new Text("Title ${widget.index}"),
          subtitle: new Text("Description ${widget.index}"),
        ),
        decoration: selected
            ? new BoxDecoration(color: Colors.black38, border: new Border.all(color: Colors.black))
            : new BoxDecoration(),
      ),
    );
  }
}

I am implementing kind of radio button in list style.

Answer 1

You cannot assign the responsibility of defining which CustomWidget is selected to the own CustomWidget. A CustomWidget must not know about the existence of other CustomWidgets, neither anything about the information they hold.

Given that, your CustomWidget should be something like this:

class CustomWidget extends StatefulWidget {
  final int index;
  final bool isSelected;
  final VoidCallback onSelect;

  const CustomWidget({
    Key key,
    @required this.index,
    @required this.isSelected,
    @required this.onSelect,
  })  : assert(index != null),
        assert(isSelected != null),
        assert(onSelect != null),
        super(key: key);

  @override
  _CustomWidgetState createState() => _CustomWidgetState();
}

class _CustomWidgetState extends State<CustomWidget> {
  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: widget.onSelect,
      child: Container(
        margin: EdgeInsets.all(5.0),
        child: ListTile(
          title: Text("Title ${widget.index}"),
          subtitle: Text("Description ${widget.index}"),
        ),
        decoration: widget.isSelected
            ? BoxDecoration(color: Colors.black38, border: Border.all(color: Colors.black))
            : BoxDecoration(),
      ),
    );
  }
}

And the widget that uses CustomWidget:

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int currentSelectedIndex;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Selected index is $currentSelectedIndex'),
      ),
      body: ListView.builder(
        itemCount: 3,
        itemBuilder: (context, index) {
          return CustomWidget(
            index: index,
            isSelected: currentSelectedIndex == index,
            onSelect: () {
              setState(() {
                currentSelectedIndex = index;
              });
            },
          );
        },
      ),
    );
  }
}