NSToolbarItem

NSToolbarItem is a class in AppKit that represents a single element in an NSToolbar. Each item can display an image with an optional label or host a custom view. It provides metadata such as a unique identifier, a localization-friendly label, and a tooltip. An item can trigger code through a target-action pair and can be enabled or disabled.

An NSToolbarItem has an itemIdentifier property (NSToolbarItem.Identifier) that identifies the item within a toolbar and is used by the toolbar to create and persist its configuration. Identifiers may refer to standard system items, such as space, flexibleSpace, or separator, or to custom application-defined values. The toolbar uses these identifiers in its delegate methods to populate the toolbar and restore user configurations.

Appearance and customization metadata include the label, paletteLabel, and toolTip. The label is the item's visible name in the toolbar when appropriate, while the paletteLabel is shown in the customization palette. The toolTip provides hover text to aid users.

NSToolbarItem supports a custom view via its view property. If a view is supplied, the toolbar displays that view instead of the standard image/label representation. The item can also provide an optional menu via the menu property to present a pop-up menu when activated.

In practice, NSToolbarItem instances are created and supplied to a toolbar by its delegate, typically through the methods that provide or customize items for given identifiers. The toolbar supports user-driven customization, allowing items to be rearranged, added, or removed, with their state and order preserved per window.