CODEWITHSUNDEEP
iphoneobjective-cios
js_
js_

Reputation: 4731

How to avoid accidental overriding method or property in Objective-C

For instance, I subclassed UILabel and added a method or property called -verticalTextAlignment to align text vertically.
And in the future, if next version of SDK or iOS added a method or property which has the same name, then it is possible my app crashs or behaves unexpectedly.

*This problem happens even if you use category instead of subclassing.

Question1
How to avoid this kind of accidental overriding in Objective-C?
I think you can avoid this by prefixing all of your methods and properties like -XXX_verticalTextAlignment. But it is not realistic, is it?

Question2
I know that this kind of accidental overriding happens at compiling time or when you update your iOS SDK, OSX SDK, or XCode.

But is it possible to happen also when updating your iPhone's iOS version?
For example, is it possible that your app runs well on iOS5 but doesn't run on iOS6 due to accidental overriding in iOS6.(You can replace iOS5 and iOS6 with any versions, for example iOS5.0 and iOS5.1)

Upvotes: 13

Views: 1130

Answers (4)

user529758
user529758

Reputation:

An elegant solution is to check for the method being already there and only adding it if it isn't: Conditional categories in Mountain Lion

Upvotes: 1

justin
justin

Reputation: 104728

Question 1a Category

Use a prefix, or avoid the whole mess and use functions instead.

Question 1b Subclass Methods

If a method does something general enough that the superclass may also implement it, I simply choose a method name which is a little more 'wordy' than Apple would conventionally choose -- such as specifying a non standard typename in the method's name. Of course, this only reduces the possibility of collision.

If you need a higher level of security, you could just test this at execution (so you know when they are introduced) and hope every user stays up to date -- or you could rely on C and/or C++ more heavily (they do not have this problem).

Question 2

But is it possible to happen also when updating your iPhone's iOS version?

Yes. It's not so unusual. When the frameworks are updated (e.g. via software update), they may contain updated frameworks. This code is loaded into the objc runtime, and you always get the version of the installed frameworks' objc implementations.

It's also a much broader problem on OS X, where you may load code and/or plugins dynamically quite easily.

Upvotes: 1

Jessedc
Jessedc

Reputation: 12470

Prefixing your category methods are the safest way to avoid these conflicts in an every growing, non namespaced cocoa ecosystem.

It's quite valid and reasonable that framework creators, open source developers and other individual developers should prefix their class methods.

Quite often I write methods prefixed with my company initials, then continue with the method.

- (void)JCMyMethodNamedSimilarToBaseClass;

Upvotes: 1

trojanfoe
trojanfoe

Reputation: 122468

  1. Yes you could use your own prefix, however that is uncommon.

  2. Yes, it can happen after an O/S update; Objective-C is a very dynamic language where messages are sent to methods rather than being called, as in other languages. These things are worked-out at runtime, not compile time.

Bottom line is yes, you might accidentally override a future base class method and the only solution is to be there when it happens and rename the method.

Upvotes: 5

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