KVO: not receiving notifications on NSTableView's -selectedRowIndexes?

Question

I'm trying to have a custom subclass of NSTableView observe the value of its own -selectedRowIndexes property, and I'm having trouble figuring out how to receive the notifications properly. My subclass looks like this (using ARC):

@implementation MyTableView

- (id)initWithCoder:(NSCoder *)aDecoder {
    if ((self = [super initWithCoder:aDecoder])) {
        [self addObserver:self forKeyPath:@"selectedRowIndexes" options:NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew context:NULL];
    }
    return self;
}

- (void)dealloc {
    [self removeObserver:self forKeyPath:@"selectedRowIndexes"];
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    NSLog(@"change: %@", change);
}

@end

However, I never see -observeValueForKeyPath:... get called. Am I missing something?

I'm also open to a better solution - the reason I want to do KVO rather than relying on the delegate's -tableViewSelectionDidChange: method is that I'd like both the previous and current values for selectedRowIndexes, rather than just being able to get the current selection. If there's a way to do that without KVO on this property, I'm all ears.

Rob Napier Rob Napier · Accepted Answer · 2012-09-12T18:59:12

If you're not seeing KVO notifications, I would open a radar at bugreport.apple.com. The reason is likely that they're not fully KVO compliant. I haven't tested, but I wouldn't be shocked.

As to how to do this without KVO, that's fairly straightforward. Use ~~tableView:willSelectRowAtIndexPath:~~ tableView:shouldSelectRow:. Check the current value, and the value to be added. Return YES.

KVO: not receiving notifications on NSTableView's -selectedRowIndexes?

2 Answers