Scoped Model - not working after go back to previous page

[syazie]

When I open the app. The app will call _callAPI() async {} since I put it in init. Then I click counter++ to add the value. Then it will show the added value in screen.then submit go to next page. when I click back page. The page will call the API then suddenly my scope model not working. when I try add value. The value not change.when I print in debug console. It did added the value.but It does not change in my screen. I think the problem is my scope model not working anymore in my app.

main.dart`class MyApp extends StatelessWidget {
@OverRide
Widget build(BuildContext context) {

final MainModel _model = MainModel();
return ScopedModel<MainModel>(
  model: _model,
    child: MaterialApp(
    title: 'Flutter Demo',
    theme: ThemeData(
    primarySwatch: Colors.blue,
  ),
  home: MyHomePage(title: 'Flutter Demo Home Page'),
),
);

}
}

class _MyHomePageState extends State {

@OverRide
void initState(){
super.initState();
fetchList().then((value){
setState(() {
_callAPI();
});
});
}

_callAPI() async {
try{
String dataURL = "url";
http.Response response = await http.get(dataURL);
}
on Exception{
}
}

Widget build(BuildContext context) {
return ScopedModelDescendant(
builder: (BuildContext context, Widget child, MainModel model) {
return Scaffold(
appBar: AppBar(
title: appBarTitle,
centerTitle: true,
actions: [
Stack(
children: [
new IconButton(icon: Icon(Icons.card_travel), onPressed: () {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => cartPage()),
);
}),
Container(
child: model.list.length != 0 ? new Positioned(
right: 11,
top: 11,
child: new Container(
padding: EdgeInsets.all(2),
decoration: new BoxDecoration(
color: Colors.red,
borderRadius: BorderRadius.circular(6),
),
constraints: BoxConstraints(
minWidth: 16,
minHeight: 16,
),
child: Text(
"${model.list.length}",
style: TextStyle(
color: Colors.white,
fontSize: 12,
),
textAlign: TextAlign.center,
),
),
) : new Container()
),
],
),
],
backgroundColor: getMainColor(),
elevation: 10.0,
),
drawer: new Drawer(
child:
_drawerLeft(context),
),
body:
Container(
),
);}
);}

Widget addValue{
      return Padding(
               padding: EdgeInsets.fromLTRB(9, 0, 0, 0),
                     child: SizedBox (
                         height:35,
                         width:35,
                         child: FloatingActionButton(   
                         heroTag: "addM",               
                            onPressed: () {
                                    Map setValue = {"var1 " : var1};          
                                    model.addInList(setValue);
				Navigator.push(
              				context,
              				MaterialPageRoute(builder: (context) => nextPage()),
            			);
                            },
                            child: Icon(
                                    Icons.add_circle_outline,
                                    color: Colors.white,
                                    size: 19,
                            ),
                         backgroundColor: getMainColor(),     
                  ),
               ),
      )
}

}`

scoped_models\main.dart
`List _list=[];

List get list{
return _list;
}

void addInList(Map newList){
_list.insert(0, newList);
notifyListeners();
}
`