stride3d/stride · error · ArgumentException

Entity shouldn't have a parent.

Error message

Entity shouldn't have a parent.

What it means

EntityManager.Add registers an entity as a root entity in the manager. It throws ArgumentException when the entity's Transform has a Parent, because entities with a parent are not roots — they belong to the hierarchy under their parent, not directly to the manager's root set.

Solutions

  1. Only add root entities (Transform.Parent == null) to the manager
  2. To relocate an entity, remove it from its current parent first (entity.Transform.Parent = null) or reparent via Transform.Parent
  3. Check entity.Transform?.Parent before calling Add

Example fix

// before
entityManager.Add(childEntity);
// after
if (childEntity.Transform?.Parent == null)
    entityManager.Add(childEntity);
else
    childEntity.Transform.Parent = null; // detach first if relocation is intended
Defensive patterns

Strategy: validation

Validate before calling

if (entity.Transform?.Parent != null) return; // not a root, skip Add
entityManager.Add(entity);

Type guard

static bool IsRootEntity(Stride.Engine.Entity e) => e?.Transform?.Parent == null;

Try / catch

try { entityManager.Add(entity); }
catch (ArgumentException ex) when (ex.Message.Contains("shouldn't have a parent")) { /* reparent or skip */ }

Prevention

When it happens

Trigger: Calling entityManager.Add(entity) where entity.Transform.Parent != null, i.e. the entity was already added as a child of another entity.

Common situations: Re-adding an entity that is a child in a scene hierarchy; moving code that assumed flat entity lists into a parented scene; scripts adding child entities to the manager directly.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/01bc00833389cb51. Report an issue: GitHub.

Appendix: source

Thrown at sources/engine/Stride.Engine/Engine/EntityManager.cs:223

                        processor.Draw(context);
                    }
                }
            }

            flexibleProcessors.Draw(context);
        }

        /// <summary>
        /// Adds the entity.
        /// If the <see cref="Entity" /> has a parent, its parent should be added (or <see cref="TransformComponent.Children" />) should be used.
        /// </summary>
        /// <param name="entity">The entity.</param>
        /// <exception cref="System.ArgumentException">Entity shouldn't have a parent.;entity</exception>
        internal void Add(Entity entity)
        {
            // Entity can't be a root because it already has a parent?
            if (entity.Transform != null && entity.Transform.Parent != null)
                throw new ArgumentException("Entity shouldn't have a parent.", nameof(entity));

            InternalAddEntity(entity);
        }

        /// <summary>
        /// Adds the specified entity.
        /// </summary>
        /// <param name="entity">The entity to add.</param>
        internal void InternalAddEntity(Entity entity)
        {
            // Already added?
            if (entities.Contains(entity))
                return;

            if (entity.EntityManager != null)
            {
                throw new InvalidOperationException("Cannot add an entity to this entity manager when it is already used by another entity manager");
            }

View on GitHub (pinned to 96fad776d2)