Re: drawRect using a Category
Re: drawRect using a Category
- Subject: Re: drawRect using a Category
- From: Peter Teeson <email@hidden>
- Date: Mon, 02 Apr 2012 11:31:44 -0400
Thank you all for your patience and kindness in educating me.
I appreciate it very much. I will sub-class which is what I have previously done.
This was, for me, a bit of an experiment (which failed). But that's also a good result.
Thanks again.
Peter
On 2012-04-02, at 12:44 AM, Jens Alfke wrote:
> On Mar 31, 2012, at 6:46 PM, Peter Teeson wrote:
>> In my app there is only the one NSMatrix instance
>
> There's no way to tell, really. For all I know, the Open or Save panels might use NSMatrix.
> Or the Find panel or the font panel. Heck, I believe in the old days of OpenStep,
> menus were implemented as NSMatrixes of menu item cells.
>
> Also, if you ever need to add another different NSMatrix somewhere else in your app,
> you're now SOL because you'll now have to rip out the category method and re-implement
> your code the right way using subclassing.
>
>> Although I do [super drawRect] after my own drawing.
>
> That won't call the old NSMatrix drawRect, it'll call the drawRect of the superclass of NSMatrix,
> which is NSControl. You've effectively deleted the original NSMatrix drawRect implementation,
> so it's impossible to call it without some tricky gymnastics. One more time: a category doesn't override
> a method, it replaces it. It literally edits the class's method table to replace the old function pointer with the new one.
> The only way to properly override a method, in the OOP sense, is to make a subclass.
>
> —Jens
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