android - Save and restore expanded/collapsed state of an ExpandableListActivity -

i have expandablelistactivity (using simplecursortreeadapter) starts activity when user clicks on child-element. when pressing back-button in new activity list-items collapsed again. how save expanded state of expandablelistactivity , restore again.

i tried implemented onsaveinstancestate() , onrestoreinstancestate() this...

@override protected void onsaveinstancestate(bundle outstate) {     super.onsaveinstancestate(outstate);     parcelable liststate = getexpandablelistview().onsaveinstancestate();     outstate.putparcelable("liststate", liststate); }   @override protected void onrestoreinstancestate(bundle state) {     super.onrestoreinstancestate(state);     parcelable liststate = state.getparcelable("liststate");     getexpandablelistview().onrestoreinstancestate(liststate); } 

...but onrestoreinstancestate() gets never called. tried restore state in oncreate() method isn't called well:

if (savedinstancestate != null) {     parcelable liststate = savedinstancestate.getparcelable("liststate");     getexpandablelistview().onrestoreinstancestate(liststate); } 

unfortunately expanded state resets whenever focus lost , oncreate() not called when gets focus again onstart(). workaround manually store ids of expanded items , expand them in onstart() again. implemented subclass of expandablelistactivity reuse behavior.

public class persistentexpandablelistactivity extends expandablelistactivity {     private long[] expandedids;      @override     protected void onstart() {         super.onstart();         if (this.expandedids != null) {             restoreexpandedstate(expandedids);         }     }      @override     protected void onstop() {         super.onstop();         expandedids = getexpandedids();     }      @override     protected void onsaveinstancestate(bundle outstate) {         super.onsaveinstancestate(outstate);         this.expandedids = getexpandedids();         outstate.putlongarray("expandedids", this.expandedids);     }      @override     protected void onrestoreinstancestate(bundle state) {         super.onrestoreinstancestate(state);         long[] expandedids = state.getlongarray("expandedids");         if (expandedids != null) {             restoreexpandedstate(expandedids);         }     }      private long[] getexpandedids() {         expandablelistview list = getexpandablelistview();         expandablelistadapter adapter = getexpandablelistadapter();         if (adapter != null) {             int length = adapter.getgroupcount();             arraylist<long> expandedids = new arraylist<long>();             for(int i=0; < length; i++) {                 if(list.isgroupexpanded(i)) {                     expandedids.add(adapter.getgroupid(i));                 }             }             return tolongarray(expandedids);         } else {             return null;         }     }      private void restoreexpandedstate(long[] expandedids) {         this.expandedids = expandedids;         if (expandedids != null) {             expandablelistview list = getexpandablelistview();             expandablelistadapter adapter = getexpandablelistadapter();             if (adapter != null) {                 (int i=0; i<adapter.getgroupcount(); i++) {                     long id = adapter.getgroupid(i);                     if (inarray(expandedids, id)) list.expandgroup(i);                 }             }         }     }      private static boolean inarray(long[] array, long element) {         (long l : array) {             if (l == element) {                 return true;             }         }         return false;     }      private static long[] tolongarray(list<long> list)  {         long[] ret = new long[list.size()];         int = 0;         (long e : list)               ret[i++] = e.longvalue();         return ret;     } } 

maybe has better solution though.