android - putExtra doesn't seem to be working at all. Using ListView to get a string and using listView to display a string -

i programming messaging app , want add users in group. however, when list of users pops , select 1 list, doesn't pass string (the username) other activity. empty list.

here code: first activity = sending data (usernames list) through putextra()

public class listusersactivity extends activity { private string currentuserid; private arrayadapter<string> namesarrayadapter; private arraylist<string> names; private listview userslistview; private button logoutbutton; private progressdialog progressdialog; private broadcastreceiver receiver = null;   @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_list_users);     parse.initialize(this, "embpz0spruv5xwdgi23innll1sghg0kznikzg6kl", "lpsu4uffpeqfxkqb1gflcij4kvg20llpgbonlise");     currentuserid = parseuser.getcurrentuser().getobjectid();     names = new arraylist<>();     parsequery<parseuser> query = parseuser.getquery();      query.wherenotequalto("objectid", currentuserid);     query.findinbackground(new findcallback<parseuser>() {         public void done(list<parseuser> userlist, com.parse.parseexception e) {             if (e == null) {                 (int i=0; i<userlist.size(); i++) {                     names.add(userlist.get(i).getusername().tostring());                 }                 userslistview = (listview)findviewbyid(r.id.userslistview);                 namesarrayadapter =                         new arrayadapter<string>(getapplicationcontext(),                                 r.layout.user_list_item, names);                 userslistview.setadapter(namesarrayadapter);                 userslistview.setonitemclicklistener(new adapterview.onitemclicklistener() {                     @override                     public void onitemclick(adapterview<?> a, view v, int i, long l) {                         intent gobacktoaddpoolintent = new intent(listusersactivity.this, addnewpoolactivity.class);                         addnewpoolactivity checker = new addnewpoolactivity();                         checker.checkifuserisselected(userslistview.getitematposition(i).tostring());                         gobacktoaddpoolintent.putextra("username", userslistview.getitematposition(i).tostring());                         startactivity(gobacktoaddpoolintent);                      }                 });             } else {                 toast.maketext(getapplicationcontext(),                         "error loading user list",                         toast.length_long).show();             }         }     });  } 

second activity = receiving data putextra()

public class addnewpoolactivity extends activity { private static arraylist<string> addedusers; private arrayadapter <string> addeduseradapter; private boolean userisselected;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_add_new_pool);     button addmembers = (button) findviewbyid(r.id.baddmembers);     addedusers = new arraylist<>();     //addedusers.add("group members");     addmembers.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {             intent showuserstoselect = new intent(addnewpoolactivity.this, listusersactivity.class);             startactivity(showuserstoselect);          }     });      listview addeduserslist = (listview) findviewbyid(r.id.addeduserslistview);      addeduseradapter = new arrayadapter<>(this, r.layout.user_list_item, addedusers);     addeduserslist.setadapter(addeduseradapter);     if(userisselected){         bundle extras = getintent().getextras();         addedusers.add(extras.getstring("username"));     }   } public void checkifuserisselected(string user){     if (user!=null){         userisselected = true;     }else{         userisselected = false;     } } 

in addition @codemagic 's answer (since boolean value false, won't call statement adding new data). it's because of parse data "username" after setadapter of listview. setting data, , trying add new data parsed list. either need before setting data set adapter, or call addedusersadapter.notifydatasetchanged() refresh listview's data set.

addeduseradapter = new arrayadapter<>(this, r.layout.user_list_item, addedusers); addeduserslist.setadapter(addeduseradapter);  bundle extras = getintent().getextras();  // check if username has been sent activity. if(extras != null && extras.containskey("username")){    addedusers.add(extras.getstring("username"));     // refresh data set    addeduseradapter.notifydatasetchanged(); }