Notification when content changes in NSOutlineView subclass

Question

I'd like to subclass NSOutlineView to show a label in the middle of itself when there is no content yet. Much like the inspectors in XCode:

Obviously I can't use the delegate methods, because I'm implementing this as a subclass and I have to be able to set the delegate to something else when using this class.

I didn't find any notifications that I could observe, except changes in the bounds property, but that's not very reliable.

Answer 1

I ended up overriding several methods of NSOutlineView to inject my code. It's not a very elegant solution, but it works. If anyone has a better solution, let me know and I might accept your answer instead.

- (void)updateEmptyLabelVisibility {
    int r = [[self dataSource] outlineView:self numberOfChildrenOfItem:nil];
    BOOL hasRows = r > 0;
    _emptyLabel.hidden = hasRows;
}

- (void)reloadItem:(id)item {
    [super reloadItem:item];
    [self updateEmptyLabelVisibility];
}

- (void)reloadData {
    [super reloadData];
    [self updateEmptyLabelVisibility];
}

- (void)awakeFromNib {
    [super awakeFromNib];
    [self updateEmptyLabelVisibility];
}

- (void)endUpdates {
    [super endUpdates];
    [self updateEmptyLabelVisibility];
}