java - No such a Instance Field in custom array list <Previewdata>...? -

how fix issue issue no such instance field custom array list.

i need fix issue i parsing data web api. api providing accurate data , parsing of json done.

  private class downloadfilestask extends asynctask<void, string, arraylist<previewdata>> {         public arraylist<previewdata> datalist = new arraylist<previewdata>() ;         private progressdialog ndialog;         constant constant = new constant();         context context;         public downloadfilestask(context context) {             this.context = context;         }          @override         protected arraylist<previewdata> doinbackground(void... params) {             note :please note string id,name , email dummy items explain question;            /*     example   */            for(int i=0;i<jsonobj.length();i++){             string id =jsonobj.get("id");             string name =jsonobj.get("name");             string email =jsonobj.get("email");             previewdata tempdata = new previewdata(id, name, email);    /* data coming in tempdata list */             datalist.add(tempdata);     /* when want add data in datalist show no such instance field*/             }            return countrylist;         }         @override         protected void onpostexecute(arraylist<previewdata> result) {            super.onpostexecute(result);            adapter = new mycustomadapter(getcontext(),r.layout.view_all_campaign_row, datalist);             /* here want add data  in adapter */             listview = (listview) view.findviewbyid(r.id.campaign_list_view);            listview.setadapter(adapter);            ndialog.dismiss();            log.i("postex",datalist.tostring());         }       }