android - ActionBar app icon as home -

i want app icon in top left return when pressed, i'm using

setdisplayhomeasupenabled(true); 

and arrow icon appears, pressing doesn't anything, why? here's oncreate:

@override protected void oncreate(bundle savedinstancestate) {     // todo auto-generated method stub     super.oncreate(savedinstancestate);     android.app.actionbar ab = getactionbar();     ab.settitle("aritmetik");     ab.setdisplayhomeasupenabled(true);     setlistadapter(new arrayadapter<string>(aritmetik.this, android.r.layout.simple_list_item_1, classes)); } 

you have override onoptionsitemselected().

@override public boolean onoptionsitemselected(menuitem item) {     switch (item.getitemid()) {         case android.r.id.home:             // app icon in action bar clicked; go home             intent intent = new intent(this, homeactivity.class);             intent.addflags(intent.flag_activity_clear_top);             startactivity(intent);             return true;         default:             return super.onoptionsitemselected(item);     } } 

(from http://developer.android.com/guide/topics/ui/actionbar.html#home)