BuildWhen<T> typedef Reading queries

Whether a reader should rebuild for a change from previous to current — the buildWhen every call style takes.

It is asked only when the value really changed: a notification carrying what the reader is already showing never rebuilds, predicate or not. When it returns false, the reader keeps showing previous — unless something else rebuilds it — and the next change is compared against what it shows.

// Rebuild only when the task's name changes:
final task = context.query(
  taskQuery(id),
  buildWhen: (previous, current) =>
      previous.dataOrNull?.name != current.dataOrNull?.name,
);