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I’m trying to clear up a lack of understanding that I clearly have about subclassing.

I have an General/NSMatrix of General/NSButtonCells already set up. Works fine - as expected. Now I want to change the behavior (a new mouse over behavior, actually). So I tried to subclass General/NSButtonCell and test by overriding mouseDown: by creating

/* General/MyButtonCell */

#import <Cocoa/Cocoa.h>

@interface General/MyButtonCell : General/NSButtonCell { } @end

#import “General/MyButtonCell.h”

@implementation General/MyButtonCell

In IB I set the various General/NSButtonCell items to my custom class of General/MYButtonCell. However when run, the check boxes exhibit the same behavior as before. Where am I going wrong?


General/NSCell (and thus General/NSButtonCell) is not a subclass of General/NSResponder, and so it doesn’t use mouseDown: or any other General/NSResponder messages. Look at the documentation/header for General/NSCell to see which methods General/NSCell uses to detect mouse clicks.

Never mind - I’m an idiot. I’m subclassing General/NSMatrix, which, in fact, actually has a mouseDown: method.

If you’d rather subclass General/NSButtonCell, take a look at the mouse tracking methods. -General/[NSCell startTrackingAt:inView:], -General/[NSCell trackMouse:inRect:ofView:untilMouseUp:], etc.

I got too cocky after I figured out how to override the mouseDown: method of the General/NSMatrix. Now I can’t figure out how to handle the mouseEntered:/mouseExited methods of my individual General/NSButtonCells in the General/NSMatrix. I subclassed General/NSButtonCell and tried to simply override those two methods, however it doesn’t seem to be working. What am I not understanding?

Again, you’re hitting the General/NSCell/General/NSControl problem. You should really check out and take a look at General/NSCell’s documentation. However, don’t take this as RTFM…I used to have a lot of the same problems as you. Basically, cells handle stuff differently than views (or responders in general), so you have to use the General/NSCell versions of the responder methods. –General/JediKnil

I really appreciate the advice. And RTFM isn’t an awful suggestion :-) but I guess there are some fundamental concepts that I still haven’t gotten a hold of. General/NSButtonCell inherits from General/NSCell, right? Perhaps I don’t know understand what mouseEntered:/mouseExited: does. Guess it’s time for me to RTFM. —- Ok, I’m trying to get a handle on startTrackingAt:inView: but it only seems to be called when the mouse is in the control AND down. Am I wrong? If not, how can I track the mouse when the mouse isn’t down.

I can read the documentation, but the likes of me really need examples sometimes.

General/NSTableViewRollover might work for an example.

Not to take away from your problem but General/CCDColoredButtonCell could use a pair of skilled eyes. I’ve been having trouble getting it working as a dataCell in an General/NSTableView - it only draws in the first row and I plain can’t figure out why.

Be sure to retain your private instance variables when subclassing (formerly titled General/ImplementingNSCopying, but that wasn’t the problem)

I was subclassing General/NSActionCell, which seemed to require me to adopt General/NSCopying in the subclass otherwise things fail when my subclass is used in a table view. Initially I did so naively, just creating a new instance, setting instance variables and continuing. I realized soon enough that this was probably wrong, since I wasn’t setting all the ivars, just my additions. So I changed it to send copyWithZone: to super, but that didn’t work at all. The cells disappeared as the table view (column) copied them but the copies … failed. I got a complaint when debugging that General/NSCFType does not respond to -drawWithFrame:inView messages.

The docs on implementing General/NSCopying told me that my strategy (alloc/int, General/NSCopyObject() or call super’s implementation) depends on the implementation of the superclass. ??? I don’t know how General/NSActionCell implements -copyWithZone:.

I was wondering whether this has something to do with subclassing Apple classes which adopt General/NSCopying. But the solution turned out to be: I wasn’t properly assigning the new private instance variables in the subclass, so they weren’t being retained.