android - AutoCompleteTextView don't show dropdown when I come back to this activity after go to another activity -

i use adapter fill autocompletetextview. @ first,everything goes fine.the autocompletetextview works fine.then want go activity work.but when come back,the autocompletetextview not show dropdown if adapter has right data. how can fix it?

  arrayadapter adapterstart;   autocompletetextview businfo_start;   autocompletetextview businfo_start;   list<autocotent> auto_list;// before code below,these variable have initialized   adapterstart = new autotipadapter(view.getcontext(),r.layout.auto_tip_item, auto_list);    businfo_start.clearlistselection();   businfo_start.clearcomposingtext();   businfo_start.setfocusable(true);   businfo_start.setadapter(adapterstart);   adapterstart.notifydatasetchanged();