EllanJiang/GameFramework · error · GameFrameworkException

Can not add child entity which is already exist.

Error message

Can not add child entity which is already exist.

What it means

AddChildEntity attaches a child entity to this entity's child list and throws if the child is already in m_ChildEntities. Duplicate children would break detach counts and hierarchy iteration, so the library fails fast instead of silently ignoring. Raised from AttachEntity when the same entity is attached twice.

Solutions

  1. Check the child's existing parent before attaching (skip if already attached to this parent).
  2. Make attach calls idempotent: guard with your own child-list check or a bool flag.
  3. Detach first, then re-attach, when re-parenting intentionally.
  4. Catch GameFrameworkException if duplicate attach is acceptable in your flow.

Example fix

// before
entityManager.AttachEntity(childId, parentId);
entityManager.AttachEntity(childId, parentId); // throws on second call
// after
if (entityManager.GetParentEntity(childId) != parentId)
{
    entityManager.AttachEntity(childId, parentId);
}
Defensive patterns

Strategy: validation

Validate before calling

if (entityManager.GetParentEntity(childId) == parentId) return; // already attached
entityManager.AttachEntity(childId, parentId);

Try / catch

try { entityManager.AttachEntity(childId, parentId); }
catch (GameFrameworkException ex) { Log.Warning("Already attached: {0}", ex.Message); }

Prevention

When it happens

Trigger: Calling EntityManager.AttachEntity(childEntityId, parentId) twice for the same pair, or attaching an entity that is already a child of that parent.

Common situations: Retry logic that re-issues AttachEntity after an ambiguous failure; UI/code paths where an attach event fires twice (e.g. double-click); missing state check when re-parenting within the same parent.

Related errors

AI-assisted analysis of EllanJiang/GameFramework@d0c010b051 (2026-09-15). Data as JSON: /api/errors/4d23e5fd9a571381. Report an issue: GitHub.

Appendix: source

Thrown at GameFramework/Entity/EntityManager.EntityInfo.cs:121

            public void GetChildEntities(List<IEntity> results)
            {
                if (results == null)
                {
                    throw new GameFrameworkException("Results is invalid.");
                }

                results.Clear();
                foreach (IEntity childEntity in m_ChildEntities)
                {
                    results.Add(childEntity);
                }
            }

            public void AddChildEntity(IEntity childEntity)
            {
                if (m_ChildEntities.Contains(childEntity))
                {
                    throw new GameFrameworkException("Can not add child entity which is already exist.");
                }

                m_ChildEntities.Add(childEntity);
            }

            public void RemoveChildEntity(IEntity childEntity)
            {
                if (!m_ChildEntities.Remove(childEntity))
                {
                    throw new GameFrameworkException("Can not remove child entity which is not exist.");
                }
            }
        }
    }
}

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