_showMultiChoiceDialog.dart

_showMultiChoiceDialog(BuildContext context) => showDialog(
      context: context,
      builder: (context) {
        final _multipleNotifier = Provider.of<MultipleNotifier>(context);
        return AlertDialog(
          title: Text("Select one country or many countries"),
          content: SingleChildScrollView(
            child: Container(
              width: double.infinity,
              child: Column(
                mainAxisSize: MainAxisSize.min,
                children: countries
                    .map((e) => CheckboxListTile(
                          title: Text(e),
                          onChanged: (value) {
                            value
                                ? _multipleNotifier.addItem(e)
                                : _multipleNotifier.removeItem(e);
                          },
                          value: _multipleNotifier.isHaveItem(e),
                        ))
                    .toList(),
              ),
            ),
          ),
          actions: [
            FlatButton(
              child: Text("Yes"),
              onPressed: () {
                Navigator.of(context).pop();
              },
            ),
          ],
        );
      },
    );