NSToolbarDelegate

NSToolbarDelegate is a protocol in Apple's AppKit that defines the interface for objects that manage an NSToolbar’s contents. A class that acts as the toolbar’s delegate provides the set of item identifiers that may appear in the toolbar, supplies the NSToolbarItem instances for those identifiers, and can respond to toolbar customization events. The delegate is typically a window controller or view controller that coordinates the toolbar with the surrounding UI.

The core responsibilities of NSToolbarDelegate include supplying item identifiers and items. The key required/delegated methods describe which items can appear and how they are created. The delegate must provide a response for the toolbar:toolbar:itemForItemIdentifier:willBeInsertedIntoToolbar:, returning an NSToolbarItem for a given identifier and configuring it (title, image, target, action). The toolbar relies on two lists to define the available and default items: toolbarAllowedItemIdentifiers: returns the identifiers that may be used in the toolbar, and toolbarDefaultItemIdentifiers: returns the default arrangement of identifiers when the toolbar is first displayed.

Several optional methods influence behavior. toolbarSelectableItemIdentifiers: can specify which items are selectable in the customization interface. The methods toolbarWillAddItem: and toolbarDidRemoveItem: notify the delegate of changes to the items as they are added or removed.

Identifiers are NSToolbarItem.Identifier values, commonly defined as strings. Items returned by the delegate are instances of NSToolbarItem or its subclass, configured with targets and actions to perform user interactions. Implementations typically cache created items and may create them lazily. Implementing NSToolbarDelegate enables flexible, dynamic toolbar configurations aligned with an app’s workflow.