Add a tooltip rectangle to NSToolBarItem's default view

Question

I have some NSToolBarItems to allow undo/redo in my app. I want them to show the name of undo/redo actions in their tooltip.

I can specify the tooltip of an NSToolBarItem vial its toolTip property. But I'm not sure when this property should be set. I haven't found a way to be notified when the undo manager has recorded a new action to undo or redo.

It would be better to dynamically return the tooltip string when the user hovers the toolbar item. But this requires adding a tooltip rectangle to a view that I cannot access. Indeed, the view property of NSToolBarItem returns nil by default. It does not return nil if I set the view property with my own view, but a NSToolBarItem uses a private subclass of NSButton as view, by default. This subclass implements nice behaviours that NSButton doesn't. So I'd rather use the default view.

Is there a way to add a tooltip rectangle to an NSToolBarItem's view that doesn't use a custom view? IOW, how can I access this view?

Answer 1

You don't need to hack NSToolbarItem. Use the NSUndoManagerCheckpointNotification notification on your undo manager. Every time it is called you can update the tooltip of the two toolbar bar items.

[NSNotificationCenter.defaultCenter addObserverForName:NSUndoManagerCheckpointNotification object:self.undoManager queue:NSOperationQueue.mainQueue usingBlock:^(NSNotification * _Nonnull note) {
    NSString *undoTitle = self.undoManager.undoMenuItemTitle;
    NSString *redoTitle = self.undoManager.redoMenuItemTitle;
    // Update the toolbar items' tooltips
}];

You can also access the relevant undo manager via note.object in the block.