android - MultiChoiceModeListener GridView selection not changing background color -

i'm following this tutorial implement multiple select in grid view, far can select items not changing background color, i've debugged code, , seems mselection null, don't know why happening

public class gridadapter extends baseadapter {      private context mcontext;     private arraylist<child> child;     imageloader imageloader = appcontroller.getinstance().getimageloader();     private hashmap<integer, boolean> mselection;       public gridadapter(context context, arraylist<child> childvalues) {         mcontext = context;         mselection = new hashmap<integer, boolean>();         child = childvalues;     }       @override     public int getcount() {         return child.size();     }      @override     public object getitem(int position) {         return position;     }      @override     public long getitemid(int arg0) {         return 0;     }      @override     public view getview(int position, view convertview, viewgroup parent) {          viewholder holder = null;         networkimageview i;          if (convertview == null) {             layoutinflater inflater = (layoutinflater) mcontext                     .getsystemservice(context.layout_inflater_service);             convertview = inflater.inflate(r.layout.child_item, null);             holder = new viewholder();              if (imageloader == null)                 imageloader = appcontroller.getinstance().getimageloader();              = (networkimageview) convertview                     .findviewbyid(r.id.flag);              i.setimageurl(string.valueof(child.get(position).getimage()), imageloader);               if (mselection.get(position) != null) {                  convertview.setbackgroundresource(r.color.bg);// selected position make red             }              convertview.settag(holder);         } else {             holder = (viewholder) convertview.gettag();         }          holder.text = (textview) convertview.findviewbyid(r.id.label);         holder.text.settext(child.get(position).getname());         return convertview;     }       static class viewholder {         textview text;     }      public void setnewselection(int position, boolean value) {         mselection.put(position, value);         notifydatasetchanged();     }      public boolean ispositionchecked(int position) {         boolean result = mselection.get(position);         return result == null ? false : result;     }      public set<integer> getcurrentcheckedposition() {         return mselection.keyset();     }      public void removeselection(int position) {         mselection.remove(position);         notifydatasetchanged();     }      public void clearselection() {         mselection = new hashmap<integer, boolean>();         notifydatasetchanged();     } } 

expandable adapter:

adapter = new gridadapter(context, listchild);         gridview.setadapter(adapter);// adapter         gridview.setchoicemode(gridview.choice_mode_multiple_modal);          gridview.setmultichoicemodelistener(new multichoicemodelistener() {             private int nr = 0;             @override             public void onitemcheckedstatechanged(actionmode mode, final int position, long id, boolean checked) {                   if (checked) {                     nr++;                     adapter.setnewselection(position, checked);                 } else {                     nr--;                     adapter.removeselection(position);                 }                 mode.settitle(nr + " rows selected!");              }               @override             public boolean oncreateactionmode(actionmode mode, menu menu) {                 mode.settitle("select items");                  return true;             }              @override             public boolean onprepareactionmode(actionmode mode, menu menu) {                 return false;             }              @override             public boolean onactionitemclicked(actionmode mode, menuitem item) {                 stringbuilder sb = new stringbuilder();                 set<integer> positions = adapter.getcurrentcheckedposition();                 (integer pos : positions) {                     sb.append(" " + pos + ",");                 }                  return false;             }              @override             public void ondestroyactionmode(actionmode mode) {                 nr = 0;                 adapter.clearselection();              }           });           gridview.setonitemclicklistener(new onitemclicklistener() {             @override             public void onitemclick(adapterview<?> parent, view view, int position, long id) {                 gridview.setitemchecked(position, !adapter.ispositionchecked(position));             }         });          return convertview;      }