How to set value on selected items with checkboxListTile

What is the correct way to Setstate of checkboxListTile to get both toggle button and added value to it?

What I want is when you check the box, You see the check button. then the value added into the base price. Please kindly help.

CheckboxListTile(
                                activeColor: Colors.blue,
                                dense: true,
                                //font change
                                title: new Text(
                                  listTopping[i].price.toStringAsFixed(0) +
                                      ' บาท',
                                  style: TextStyle(
                                    fontSize: 25,
                                    fontWeight: FontWeight.bold,
                                  ),
                                ),
                                value: listTopping[i].isCheck,
                                secondary: Container(
                                  height: 50,
                                  width: 300,
                                  child: Text(
                                    listTopping[i].topping,
                                    style: TextStyle(
                                      fontSize: 25,
                                      fontWeight: FontWeight.bold,
                                    ),
                                  ),
                                ),
                                onChanged: (bool? val) {
                                  itemChange(val!, i);
                                },
                              ),

Here is the setstate that I believe is wrong...

  void itemChange(bool val, int i) {
    setState(() {
      listTopping[i].isCheck = val;
    });
  }
}