NSCell Custom Highlight

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.

Pidgin

Are you sending [super drawInteriorWithFrame:cellFrame inView:controlView]; (with whatever parameter names you’re using) after you’ve drawn your custom background? – Haveman

@Bavarious - If I do that then the custom background is lost. Result is the same as the second screenshot as I'd presume that method draws its own background too. – Pidgin

Ah, gotcha. Can’t you set a transparent highlight colour so that super won’t mess with your custom highlight, and then you use -isHighlighted inside -drawInterior… to decide how you should draw the background? – Haveman

@Bavarious - Interesting idea. Returning [NSColor clearColor] for highlightColorWithFrame:inView: just showed through to the desktop like i.imgur.com/jy970.png. However, returning nil for the same method did what I wanted - i.imgur.com/joUom.png - thanks for your help! – Pidgin

Cheers! May I suggest you describe what you’ve done as an answer and accept it? – Haveman

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).

Pidgin

How exactly you draw background ? I only can change the text color. I have used ... ` if( [self isHighlighted] ) { NSColor *oldColor = [self backgroundColor]; [self setBackgroundColor:[NSColor whiteColor]]; [super drawWithFrame:cellFrame inView:controlView]; [self setBackgroundColor:oldColor]; } ` but nothing happens! Thanks... – Yowl

Have you actually overridden -drawInteriorWithFrame:inView: rather than -drawWithFrame:inView:? – Machos

How do you do this with Swift? It's not possible to return nil from highlightColorWithFrame!!!! – Crooks