@Override
 public boolean onOptionsItemSelected(MenuItem item) {
   switch (item.getItemId()) {
     case R.id.menu_scan:
       mLeDeviceListAdapter.clear();
       scanLeDevice(true);
       break;
     case R.id.menu_stop:
       scanLeDevice(false);
       break;
   }
   return true;
 }
 @Override
 protected void onPause() {
   super.onPause();
   scanLeDevice(false);
   mLeDeviceListAdapter.clear();
 }