Re: Why can't I use any object as a key in a dictionary?
Re: Why can't I use any object as a key in a dictionary?
- Subject: Re: Why can't I use any object as a key in a dictionary?
- From: Roland King <email@hidden>
- Date: Mon, 01 Feb 2010 16:26:53 +0800
Tollfree Bridging is a little more complicated than that. They may end
up being the same object under the covers, but even if they are, the
NSDictionary version doesn't come with the range of options that the
CFDictionary does. Just make a CFDictionary(), the default for it is to
retain keys (and values) so it's actually really, really easy; I use
them all over the place for stuff like this.
If a have a non-NSDictionary compatible CFDictionary() like that by the
way I use toll free bridging for reading values from it, but I don't use
it for setting them, it doesn't seem to work.
By the way, CALayer is a KVC compliant class so you can in fact just
store a reference to an arbitrary object in it with
[ layer setValue:value forKey:@"KeyForObjectAssociatedWithLayer" ];
and save yourself a whole world of pain.
Richard Penwell wrote:
I thought NSDictionary and CFDictionary were the same data object, that whole toll free bridging...
An ugly hack would be to cast the pointer to a numeric type, and encode that in a NSNumber... but I would feel very very ashamed of doing so.
On Feb 1, 2010, at 3:10 AM, Roland King wrote:
Because NSDictionary requires keys to be copyable because it copies them (it's in the documentation). Use a CFDictionary() instead, you can set it up to retain the keys and do what you want.
Rick Mann wrote:
I'd like to use a CALayer object as a key in a dictionary. The reason is that when my app detects a hit in a layer, I need to quickly determine which object I've associated with it. Since I can't store a reference to an arbitrary object in the CALayer, a dictionary seems to be the most expedient way to do that.
Unfortunately, I can't seem to add my layer as the key (it fails with "-[CALayer copyWithZone:]: unrecognized selector sent to instance 0x50132a0"). It's really pretty handy to be able to use any object as a key, why is this not the case in Obj-C?
TIA,
Rick
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