Image item validation

The toolbar automatically takes care of darkening an image item when it is clicked and fading it when it is disabled. All your code has to do is validate the item. If an image item has a valid target/action pair, then the toolbar will call NSToolbarItemValidation’s validateToolbarItem: on target if the target implements it; otherwise the item is enabled by default.

In the absence of a custom menu form representation, NSToolbar validates an image item’s overflow menu in the same way that it validates the toolbar item in the toolbar.

View item validation

Validation for view items is not automatic because a view item can be of unknown complexity. To implement validation for a view item, you must subclass NSToolbarItem and override validate (because NSToolbarItem’s implementation of validate does nothing for view items). In your override method, do the validation specific to the behavior of the view item and then enable or disable whatever you want in the contents of the view accordingly. If the view is an NSControl you can call setEnabled:, which will in turn call setEnabled: on the control.

In the absence of a custom menu form representation, NSToolbar by default disables a view item’s overflow menu item.

Overflow menu item validation

If a toolbar item has a custom menu form representation with no submenu, then the toolbar will validate the overflow menu item and the toolbar item’s text in Text Only Mode differently than it would with the default menu form representation: If the menu form representation menu item’s target implements validateMenuItem: (part of NSMenuValidation), the toolbar calls that method to validate both the overflow menu item and the toolbar item’s text in Text Only Mode.