@Override
 protected void onDestroy() {
   super.onDestroy();
   LoadBlocks.forgetActivity();
 }
 static void forgetActivity() {
   for (LoadBlocks loadBlocks : inFlight) {
     loadBlocks.activityOrNull = null;
   }
   inFlight.clear();
 }
 @Override
 protected void onResume() {
   super.onResume();
   LoadBlocks.load(this);
 }