FLevelObjectsObserver | Unreal Engine 5.2 Documentation

API > API/Plugins > API/Plugins/ModelingComponentsEditorOnly > API/Plugins/ModelingComponentsEditorOnly/Scene

Inheritance Hierarchy

FEditorUndoClient
FLevelObjectsObserver

References


Module	ModelingComponentsEditorOnly
Header	/Engine/Plugins/Runtime/MeshModelingToolset/Source/ModelingComponentsEditorOnly/Public/Scene/LevelObjectsObserver.h
Include	#include "Scene/LevelObjectsObserver.h"

Syntax

class FLevelObjectsObserver : public FEditorUndoClient

Remarks

FLevelObjectsObserver is a utility class that tracks the active-set of Actors in a World, in the Editor, and emits events when the set changes. The goal is to guarantee that:

OnActorAdded will be emitted when an Actor comes into existence
OnActorRemoved will be emitted when an Actor ceases to exist (possibly after GC, though)
these signals will be unique, ie once per Actor

This is a surprisingly complicated problem in the Editor due to the many ways that Actors might be created or destroyed, in particular via Undo/Redo.

Note that it is not possible to guarantee that OnActorRemoved() fires before an Actor is GC'd. So, listeners should maintain TWeakObjectPtr<>'s on Actors if they need to know this information.

Variables

Type	Name	Description
TSet< AActor * >	Actors
FActorAddRemoveSignature	OnActorAdded	OnActorAdded is emitted when a new Actor is detected
FDelegateHandle	OnActorAddedHandle
FDelegateHandle	OnActorDeletedHandle
FDelegateHandle	OnActorListChangedHandle
FActorAddRemoveSignature	OnActorRemoved	OnActorRemoved is emitted when an existing Actor is destroyed.
UWorld *	World

Destructors

	Type	Name	Description
		~FLevelObjectsObserver ()	Destructor.

Functions

Type	Name	Description
void	HandleActorAddedEvent ( AActor* Actor )
void	HandleActorDeletedEvent ( AActor* Actor )
void	Initialize ( UWorld* WorldIn )	Begin watching WorldIn. This will emit OnActorAdded for all Actors in the World.
void	OnUntrackedLevelChange ()
void	Shutdown ()	Stop watching WorldIn.