expandParentsThatGainedChildren<TKey, TData> function

void expandParentsThatGainedChildren<TKey, TData>({ required TreeController<TKey, TData> controller, required Map<TKey, List<TKey>> oldChildrenByParent, required Map<TKey, List<TKey>> newChildrenByParent, required Set<TKey> rememberedBeforeSync, required bool animate, })

Auto-expands parents whose first children appeared in the most recent sync.

Iterates newChildrenByParent and expands every parent that:

• has at least one child in the new state, AND
• had zero children in oldChildrenByParent (so this is a genuine first-children gain, not a sibling addition), AND
• was NOT in rememberedBeforeSync (so we don't override a user's deliberate collapse that the sync controller will restore on its own), AND
• currently exists in the controller and is not already expanded.

The iteration is wrapped in TreeController.runBatch so K gained-children parents produce one structural notification instead of K separate fan-outs across every mounted row.

Used by both SyncedSliverTree and SectionedSliverList. Keep the rules in one place — the rememberedBeforeSync filter exists to prevent silently re-expanding a user-collapsed, re-added subtree, and duplicating that logic risks divergence.

Implementation

void expandParentsThatGainedChildren<TKey, TData>({
  required TreeController<TKey, TData> controller,
  required Map<TKey, List<TKey>> oldChildrenByParent,
  required Map<TKey, List<TKey>> newChildrenByParent,
  required Set<TKey> rememberedBeforeSync,
  required bool animate,
}) {
  controller.runBatch(() {
    for (final entry in newChildrenByParent.entries) {
      final parentKey = entry.key;

      if (entry.value.isEmpty) {
        continue;
      }

      final oldChildren = oldChildrenByParent[parentKey];
      final hadChildrenBefore = oldChildren != null && oldChildren.isNotEmpty;
      if (hadChildrenBefore) {
        continue;
      }

      if (rememberedBeforeSync.contains(parentKey)) {
        continue;
      }

      if (controller.getNodeData(parentKey) != null &&
          !controller.isExpanded(parentKey)) {
        controller.expand(key: parentKey, animate: animate);
      }
    }
  });
}