update checkbox and return value from dialogue flutter

I am trying to add some city list to a dialogue with checkbox so that i need to implement multiple click on items. what i am trying to do is given below.

onPressed from button calls Rest Service and on success result i just show a dialogue

void showCityDialog(BuildContext context) {
    SimpleDialog dialog = new SimpleDialog(
      title: Row(
        mainAxisAlignment: MainAxisAlignment.spaceBetween,
        children: <Widget>[
          new Text(
            "CITIES",
            style: TextStyle(fontSize: 18.0, color: Colors.black),
            textAlign: TextAlign.center,
          ),
          new RaisedButton(
            onPressed: () {print("clicked");},
            color: Color(0xFFfab82b),
            child: new Text(
              "Done",
              style: TextStyle(color: Colors.white),
            ),)],),
      children: <Widget>[
        Column(
          mainAxisAlignment: MainAxisAlignment.start,
          crossAxisAlignment: CrossAxisAlignment.start,
          children: <Widget>[
            new Container(
              constraints: BoxConstraints(maxHeight: 500.0),
              child: ListView.builder(
                scrollDirection: Axis.vertical,
                itemCount: cityData.length,
                itemBuilder: (context, position) {
                  return new CheckboxListTile(
                    value: checkboxValueCity,
                    onChanged: (bool value) {
                      setState(() {
                        checkboxValueCity = value;
                      });
                    },
                    activeColor: Color(0xFFfab82b),
                    dense: true,
                    title: Text(
                      cityData[position].city_name,
                      style: TextStyle(fontSize: 16.0, color: Colors.black),
                    ),);},),),],)],);
    showDialog(
        context: context,
        builder: (BuildContext context) {
          return dialog;
        });
  }

checkboxValueCity is a boolean variable in class , on click of chekboxListItem i need to update checkbox value as checked and uncheced. At the same time need to add/remove that item to a list which is also inside that class.

But in my code checkbox is not refershing on every click but when i close that box and open it again checkbox is checked. then how can i get multiple click from tile and how can i return list from dialogue?