java - How to load child items while click parent item in ExpandableListView -

i new android, have expandablelistview in app. want load child items while click parent item. tried alot not working . please help.

my code here:

expandablelistadapter listadapter; expandablelistview explistview; list<string> listdataheader; hashmap<string, list<string>> listdatachild;  public view oncreateview(layoutinflater inflater, viewgroup container,                          bundle savedinstancestate) {     view view = inflater.inflate(r.layout.faq, container, false);     // listview     explistview = (expandablelistview) view.findviewbyid(r.id.faqlist);     preparelistdata();     listadapter = new expandablelistadapter(getactivity(),listdataheader,listdatachild);     // setting list adapter     explistview.setadapter(listadapter);      // listview group expanded listener     explistview.setongroupexpandlistener(this);     return view; }  private void preparedata(string s) {     log.d("working:","yes");      listdatachild = new hashmap<string, list<string>>();    // adding child data     list<string> top250 = new arraylist<string>();     if(s.equals("top 250")){         top250 = new arraylist<string>();         top250.add("the shawshank redemption godfather");     }else if(s.equals("now showing")){         top250 = new arraylist<string>();         top250.add("the conjuring welcome world of india");     }else if(s.equals("coming soon..")){         top250 = new arraylist<string>();         top250.add("2 guns of indias");     }else {         top250 = new arraylist<string>();         top250.add("nothing");     }     listdatachild.put(listdataheader.get(0), top250); // header, child data     listdatachild.put(listdataheader.get(1), top250);     listdatachild.put(listdataheader.get(2), top250); }  private void preparelistdata() {     listdataheader = new arraylist<string>();     listdatachild = new hashmap<string, list<string>>();      // adding child data     listdataheader.add("top 250");     listdataheader.add("now showing");     listdataheader.add("coming soon..");      // adding child data     list<string> top250 = new arraylist<string>();     top250.add("the shawshank redemption");     top250.add("the godfather");     top250.add("the godfather: part ii");     top250.add("pulp fiction");     top250.add("the good, bad , ugly");     top250.add("the dark knight");     top250.add("12 angry men");      list<string> nowshowing = new arraylist<string>();     nowshowing.add("the conjuring");     nowshowing.add("despicable me 2");     nowshowing.add("turbo");     nowshowing.add("grown ups 2");     nowshowing.add("red 2");     nowshowing.add("the wolverine");      list<string> comingsoon = new arraylist<string>();     comingsoon.add("2 guns");     comingsoon.add("the smurfs 2");     comingsoon.add("the spectacular now");     comingsoon.add("the canyons");     comingsoon.add("europa report");      listdatachild.put(listdataheader.get(0), top250); // header, child data     listdatachild.put(listdataheader.get(1), nowshowing);     listdatachild.put(listdataheader.get(2), comingsoon); }  @override public void ongroupexpand(int groupposition) {      preparedata(listdataheader.get(groupposition));     listadapter = new expandablelistadapter(getactivity(),listdataheader,listdatachild);     listadapter.notifydatasetchanged();     // setting list adapter     explistview.setadapter(listadapter);     toast.maketext(getactivity().getapplicationcontext(),listdataheader.get(groupposition) + " expanded",             toast.length_short).show();  } 

thanks in advance!

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