Can I tag a UIColor?

Question

Can I tag a UIColor that is constantly changing values for easy access from methods?

Answer 1

As of iPhone SDK 3.1, you can use objc_setAssociatedObject. You'd do something like:

objc_setAssociatedObject(myColor, infoObject, &keyObject, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

Note 1: the value must be an object. You can't set an integer as the value.

To retrieve the value:

id aTag = objc_getAssociatedObject(myColor, &keyObject);

Note 2: the keyObject must exactly the same object that you used when setting the value. It won't work if you send in another object with the same value.

If you later want to release the tag value:

objc_setAssociatedObject(myColor, nil, &keyObject, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

(Due to a bug this doesn't work in the iPhone simulator. See this question for more info.)

You can also read this post which touches on using this method for storing keys.

Note: I'm not saying this is the best way of handling the problem. As the Objective-C programming guide states, associated objects are mainly intended for situations where

you do not have access to the source code for the class, or if for binary-compatibility reasons you cannot alter the layout of the object.

Read all about it here.