Selection History (Back/Forward Navigation)

Role

SelectionService records each selection change as a SelectionOperation on its own ITransactionStack, completely separate from undo/redo. Rolling back that stack restores the previous selection; rolling forward restores the next. The stack has unlimited capacity and is never surfaced in the undo/redo history. From the user's perspective, this is the back/forward navigation in GameStudio.

Key Types

Type	Assembly	Purpose
SelectionService	Stride.Core.Assets.Editor sources/editor/Stride.Core.Assets.Editor/Services/	Owns the navigation stack; exposes NavigateBackward / NextSelection; registers observable collections to track
SelectionState	same	Snapshot of all registered collection states at a point in time; HasValidSelection() checks whether the referenced objects still exist
SelectionScope	same	A group of INotifyCollectionChanged collections tracked together as a unit; always obtained from RegisterSelectionScope(), never constructed directly
SelectionOperation	sources/editor/Stride.Core.Assets.Editor/Services/SelectionOperation.cs	Operation subclass pairing a previous and next SelectionState; Rollback restores previous, Rollforward restores next

How It Works

RegisterSelectionScope() subscribes the service to one or more observable collections. Each time any of those collections changes, the service captures a SelectionState snapshot (recording the current contents of all registered collections) and pushes a SelectionOperation wrapping the previous and new states.

NavigateBackward() keeps rolling back while the resulting state either still equals the state it started from (the rollback had no observable effect on the selection) or has no valid selection (HasValidSelection() returns false). This means both no-op entries and entries whose objects have been deleted are skipped transparently.

NextSelection() does the same in the rollforward direction.

SelectionService Members

Member	Type	Purpose
CanGoBack	bool	Whether the navigation stack can roll back
CanGoForward	bool	Whether the navigation stack can roll forward
NavigateBackward()	void	Roll back to the previous valid selection state
NextSelection()	void	Roll forward to the next valid selection state
RegisterSelectionScope(idToObject, objectToId, collections)	SelectionScope	Hook the service into observable collections; idToObject/objectToId maps allow states to be serialised using AbsoluteId without holding strong object references

Access via ServiceProvider.Get<SelectionService>(). This is the concrete class — there is no ISelectionService interface.

Note that NextSelection() does not follow the Navigate prefix used by its counterpart NavigateBackward() — this asymmetry is in the source API itself, not a documentation error.

RegisterSelectionScope is typically called by the editor framework when setting up an editor panel or session, not by individual contributor code. The idToObject and objectToId parameters are Func<AbsoluteId, object> and Func<object, AbsoluteId?> — they map between runtime object references and stable AbsoluteId values (defined in Stride.Core.Assets) so that selection states survive object reloads.

Relationship to Undo/Redo

The two systems share ITransactionStack and Operation from Stride.Core.Transactions but use completely separate instances:

• Undoing a mutation does not move the navigation cursor.
• Navigating back does not undo any mutation.
• The navigation stack has no DirtyingOperation or IDirtiable involvement — selection is not a dirtying action.

SelectionService uses a raw ITransactionStack (not IUndoRedoService) with capacity int.MaxValue. It does not use DirtyingOperation or AnonymousDirtyingOperation.

Assembly Placement

SelectionService, SelectionState, SelectionScope, and SelectionOperation all live in Stride.Core.Assets.Editor at sources/editor/Stride.Core.Assets.Editor/Services/.