@Override
 protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_main);
   mExplosionField = ExplosionField.attach2Window(this);
   addListener(findViewById(R.id.root));
 }
 @Override
 public boolean onOptionsItemSelected(MenuItem item) {
   if (item.getItemId() == R.id.action_reset) {
     View root = findViewById(R.id.root);
     reset(root);
     addListener(root);
     mExplosionField.clear();
     return true;
   }
   return super.onOptionsItemSelected(item);
 }