Question

I’m trying to subclass NSCell to draw a custom background highlight. The documentation seems to suggest that the overriding highlight:withFrame:inView: should allow me to do this but the method is never called.

Instead, I’ve overridden drawInteriorWithFrame:inView: which works fine – I can draw what I want in the cell. However, the issue is that I have to draw everything myself, losing the functionality of the type of NSCell I am extending – for example an NSTextFieldCell’s ability to display text:

Custom drawn highlighted cell:

However, I just want to redraw the background (the highlight), and retain the ability to use the main functionality of the extended cell:

I could, of course, just draw the text myself too but I’m hoping there is an easier way of doing this.

Any help is much appreciated.

Answer 1

Thanks to the help of @Bavarious I’ve managed to work it out. My extended NSTextFieldCell class implementation now contains:

-(NSColor *)highlightColorWithFrame:(NSRect)cellFrame inView:(NSView *)controlView {
    return nil;
}

- (void)drawWithFrame:(NSRect)cellFrame inView:(NSView *)controlView {
    if ([self isHighlighted]) {
        // Draw highlight background here
    }

    [super drawInteriorWithFrame:cellFrame inView:controlView];
}

The key is to make sure you return nil for highlightColorWithFrame:inView: to stop drawInteriorWithFrame:inView: drawing a background and yet still calling it to draw the main content (in this case text).