shouldRebuild method

bool shouldRebuild(BuildWhen<T>? buildWhen)

Whether what the controller holds now is worth a frame, given what read last recorded.

• Nothing read yet: yes.
• The observed state equal to the one built: no, before buildWhen is even asked. The first build reads the result straight after the subscribe started the fetch, and the observer's notification about that very fetch arrives after the frame — a rebuild with nothing new in it. Results carry value equality, so "nothing new" is ==.
• What is beside the value moved, with the value or without it: yes, before buildWhen is asked. It cannot judge what it is not shown, and a "no" would leave the reader showing the stale half — "Load more" with no next page. Without a beside, the same holds when the observed state moved and the value is equal.
• Otherwise, as buildWhen says; with none, yes.

Implementation

bool shouldRebuild(BuildWhen<T>? buildWhen) {
  if (!_recorded) {
    return true;
  }
  if (_observedState() == _builtState) {
    return false;
  }
  final beside = _beside;
  if (beside != null && beside() != _builtBeside) {
    return true;
  }
  final current = _value();
  if (current == _built) {
    return true;
  }
  return buildWhen == null || buildWhen(_built, current);
}