BEFORE-event args for WhiteboardState.ItemAdding$. Raised by WhiteboardState.AddItem (and therefore also by WhiteboardState.Highlight and WhiteboardState.DuplicateItem, which add through it) before anything is stamped or stored. Handlers may mutate Input (e.g. clamp coordinates, rewrite text) — the engine adds whatever the args carry after the emit — or set Cancel to veto the add entirely (the caller receives null).
Cancel
null
Who is adding the item.
Set to true (in a synchronous handler) to veto the operation.
true
The item about to be added (no ID / Z / Author yet — the engine stamps those).
BEFORE-event args for WhiteboardState.ItemAdding$. Raised by WhiteboardState.AddItem (and therefore also by WhiteboardState.Highlight and WhiteboardState.DuplicateItem, which add through it) before anything is stamped or stored. Handlers may mutate Input (e.g. clamp coordinates, rewrite text) — the engine adds whatever the args carry after the emit — or set
Cancelto veto the add entirely (the caller receivesnull).